RESUMO
Tributyltin (TBT) is an organotin environmental pollutant widely used as an agricultural and wood biocide and in antifouling paints. Countries began restricting TBT use in the 2000s, but their use continues in some agroindustrial processes. We studied the acute effect of TBT on cardiac function by analyzing myocardial contractility and Ca2+ handling. Cardiac contractility was evaluated in isolated papillary muscle and whole heart upon TBT exposure. Isolated ventricular myocytes were used to measure calcium (Ca2+) transients, sarcoplasmic reticulum (SR) Ca2+ content and SR Ca2+ leak (as Ca2+ sparks). Reactive oxygen species (ROS), as superoxide anion (O2â¢-) was detected at intracellular and mitochondrial myocardium. TBT depressed cardiac contractility and relaxation in papillary muscle and intact whole heart. TBT increased cytosolic, mitochondrial ROS production and decreased mitochondrial membrane potential. In isolated cardiomyocytes TBT decreased both Ca2+ transients and SR Ca2+ content and increased diastolic SR Ca2+ leak. Decay of twitch and caffeine-induced Ca2+ transients were slowed by the presence of TBT. Dantrolene prevented and Tiron limited the reduction in SR Ca2+ content and transients. The environmental contaminant TBT causes cardiotoxicity within minutes, and may be considered hazardous to the mammalian heart. TBT acutely induced a negative inotropic effect in isolated papillary muscle and whole heart, increased arrhythmogenic SR Ca2+ leak leading to reduced SR Ca2+ content and reduced Ca2+ transients. TBT-induced myocardial ROS production, may destabilize the SR Ca2+ release channel RyR2 and reduce SR Ca2+ pump activity as key factors in the TBT-induced negative inotropic and lusitropic effects.
Assuntos
Cardiotoxicidade/metabolismo , Compostos de Trialquitina/toxicidade , Poluentes Químicos da Água/toxicidade , Animais , Cálcio/metabolismo , Mitocôndrias/metabolismo , Contração Miocárdica , Miocárdio/metabolismo , Miócitos Cardíacos/efeitos dos fármacos , Estresse Oxidativo/fisiologia , Espécies Reativas de Oxigênio/metabolismo , Canal de Liberação de Cálcio do Receptor de Rianodina , Retículo Sarcoplasmático/metabolismoRESUMO
The cardiac sarcolemmal Na-Ca exchanger (NCX) is allosterically regulated by [Ca](i) such that when [Ca](i) is low, NCX current (I(NCX)) deactivates. In this study, we used membrane potential (E(m)) and I(NCX) to control Ca entry into and Ca efflux from intact cardiac myocytes to investigate whether this allosteric regulation (Ca activation) occurs with [Ca](i) in the physiological range. In the absence of Ca activation, the electrochemical effect of increasing [Ca](i) would be to increase inward I(NCX) (Ca efflux) and to decrease outward I(NCX). On the other hand, Ca activation would increase I(NCX) in both directions. Thus, we attributed [Ca](i)-dependent increases in outward I(NCX) to allosteric regulation. Ca activation of I(NCX) was observed in ferret myocytes but not in wild-type mouse myocytes, suggesting that Ca regulation of NCX may be species dependent. We also studied transgenic mouse myocytes overexpressing either normal canine NCX or this same canine NCX lacking Ca regulation (Delta680-685). Animals with the normal canine NCX transgene showed Ca activation, whereas animals with the mutant transgene did not, confirming the role of this region in the process. In native ferret cells and in mice with expressed canine NCX, allosteric regulation by Ca occurs under physiological conditions (K(mCaAct) = 125 +/- 16 nM SEM approximately resting [Ca](i)). This, along with the observation that no delay was observed between measured [Ca](i) and activation of I(NCX) under our conditions, suggests that beat to beat changes in NCX function can occur in vivo. These changes in the I(NCX) activation state may influence SR Ca load and resting [Ca](i), helping to fine tune Ca influx and efflux from cells under both normal and pathophysiological conditions. Our failure to observe Ca activation in mouse myocytes may be due to either the extent of Ca regulation or to a difference in K(mCaAct) from other species. Model predictions for Ca activation, on which our estimates of K(mCaAct) are based, confirm that Ca activation strongly influences outward I(NCX), explaining why it increases rather than declines with increasing [Ca](i).
Assuntos
Cálcio/metabolismo , Fibras Musculares Esqueléticas/metabolismo , Miocárdio/citologia , Trocador de Sódio e Cálcio/química , Trocador de Sódio e Cálcio/metabolismo , Regulação Alostérica/fisiologia , Animais , Transporte Biológico/efeitos dos fármacos , Transporte Biológico/fisiologia , ATPases Transportadoras de Cálcio/metabolismo , Simulação por Computador , Citosol/metabolismo , Cães , Furões , Camundongos , Modelos Biológicos , Fibras Musculares Esqueléticas/citologia , Mutagênese/fisiologia , Níquel/farmacologia , Retículo Sarcoplasmático/metabolismo , Trocador de Sódio e Cálcio/genéticaRESUMO
BACKGROUND: The Na(+)/Ca(2+) exchange (NCX) extrudes Ca(2+) from cardiac myocytes, but it can also mediate Ca(2+) influx, load the sarcoplasmic reticulum with Ca(2+), and trigger Ca(2+) release from the sarcoplasmic reticulum. In ischemia/reperfusion or digitalis toxicity, increased levels of intracellular [Na(+)] ([Na(+)](i)) may raise levels of intracellular [Ca(2+)] ([Ca(2+)](i)) via NCX, leading to cell injury and arrhythmia. METHODS AND RESULTS: We used KB-R7943 (KBR) to selectively block Ca(2+) influx via NCX to study the role of NCX-mediated Ca(2+) influx in intact rat ventricular myocytes. Removing extracellular Na(+) caused [Ca(2+)](i) to rise, due to Ca(2+) influx via NCX, and this was blocked by 90% with 5 micromol/L KBR. However, KBR did not alter [Ca(2+)](i) decline due to NCX. Thus, we used 5 micromol/L KBR to selectively block Ca(2+) entry but not efflux via NCX. Under control conditions, 5 micromol/L KBR did not alter steady-state twitches, Ca(2+) transients, Ca(2+) load in the sarcoplasmic reticulum, or rest potentiation, but it did prolong the late low plateau of the rat action potential. When Na(+)/K(+) ATPase was inhibited by strophanthidin, KBR reduced diastolic [Ca(2+)](i) and abolished the spontaneous Ca(2+) oscillations, but it did not prevent inotropy. CONCLUSIONS: In rat ventricular myocytes, Ca(2+) influx via NCX is not important for normal excitation-contraction coupling. Furthermore, the inhibition of Ca(2+) efflux alone (as [Na(+)](i) rises) may be sufficient to cause glycoside inotropy. In contrast, Ca(2+) overload and spontaneous activity at high [Na(+)](i) was blocked by KBR, suggesting that net Ca(2+) influx (not merely reduced efflux) via NCX is involved in potentially arrhythmogenic Ca(2+) overload.
Assuntos
Cálcio/metabolismo , Contração Miocárdica/efeitos dos fármacos , Miocárdio/metabolismo , Trocador de Sódio e Cálcio/antagonistas & inibidores , Tioureia/análogos & derivados , Animais , Glicosídeos/farmacologia , Técnicas In Vitro , Masculino , Miocárdio/citologia , Ratos , Ratos Sprague-Dawley , Retículo Sarcoplasmático/metabolismo , Tioureia/farmacologiaRESUMO
We have characterized [Ca](i) decline in voltage-clamped rabbit ventricular myocytes with progressive increases in sarcoplasmic reticulum (SR) calcium load. "Backflux" through the SR calcium pump is a critical feature which allows realistically small values for SR calcium leak fluxes to be used. Total cytosolic calcium was calculated from the latter part of [Ca](i) decline using rate constants for cellular calcium buffers. Intra-SR calcium buffering characteristics were also deduced. We found that the net SR calcium pump flux and rate of [Ca](i) decline decreased as the SR free [Ca] rose, with pump parameters held constant. We have therefore characterized for the first time in intact myocytes both forward and reverse SR calcium pump kinetics as well as intra-SR calcium buffering and SR calcium leak. We conclude that the reverse flux through the SR calcium pump is an important factor in comprehensive understanding of dynamic SR calcium fluxes.
Assuntos
ATPases Transportadoras de Cálcio/metabolismo , Cálcio/metabolismo , Coração/fisiologia , Miocárdio/metabolismo , Retículo Sarcoplasmático/enzimologia , Animais , Células Cultivadas , Citosol/metabolismo , Ventrículos do Coração , Membranas Intracelulares/fisiologia , Membranas Intracelulares/ultraestrutura , Cinética , Técnicas de Patch-Clamp , Coelhos , Retículo Sarcoplasmático/ultraestrutura , Troponina/metabolismoRESUMO
Our aim was to measure the influence of sarcoplasmic reticulum (SR) calcium content ([Ca](SRT)) and free SR [Ca] ([Ca](SR)) on the fraction of SR calcium released during voltage clamp steps in isolated rabbit ventricular myocytes. [Ca](SRT), as measured by caffeine application, was progressively increased by conditioning pulses. Sodium was absent in both the intracellular and in the extracellular solutions to block sodium/calcium exchange. Total cytosolic calcium flux during the transient was inferred from I(Ca), [Ca](SRT), [Ca](i), and cellular buffering characteristics. Fluxes via the calcium current (I(Ca)), the SR calcium pump, and passive leak from the SR were evaluated to determine SR calcium release flux (J(rel)). Excitation-contraction (EC) coupling was characterized with respect to both gain (integral J(rel)/integral I(Ca)) and fractional SR calcium release. Both parameters were virtually zero for a small, but measurable [Ca](SRT). Gain and fractional SR calcium release increased steeply and nonlinearly with both [Ca](SRT) and [Ca](SR). We conclude that potentiation of EC coupling can be correlated with both [Ca](SRT) and [Ca](SR). While fractional SR calcium release was not linearly dependent upon [Ca](SR), intra-SR calcium may play a crucial role in regulating the SR calcium release process.
Assuntos
Cálcio/metabolismo , Coração/fisiologia , Retículo Sarcoplasmático/fisiologia , Animais , Cafeína/farmacologia , Citosol/metabolismo , Coração/efeitos dos fármacos , Ventrículos do Coração , Cinética , Contração Miocárdica , Miocárdio/metabolismo , Técnicas de Patch-Clamp , Coelhos , Retículo Sarcoplasmático/efeitos dos fármacosRESUMO
Most insecticides are neurotoxicants causing various forms of hyperexcitation and paralysis in animals. A variety of neuroreceptors and ion channels have been identified as the major target sites of these neurotoxic insecticides. This paper gives the highlights of some of the recent development in this area. Pyrethroids keep the sodium channel open for unusually long times causing a prolonged flow of sodium current. The prolonged sodium current elevates and prolongs the depolarizing after-potential which reaches the threshold membrane potential to initiate repetitive after-discharges. We have developed the method with which the percentage of sodium channel population that needs to be modified to cause repetitive after-discharges can be measured accurately. In rat cerebellar Purkinje neurons, only 0.6% of sodium channels needs to be modified for hyperexcitation resulting in a large toxicity amplification. This concept is applicable to other neuroactive drugs that act through the threshold phenomenon. The mechanisms of selective toxicity of pyrethroids in mammals and insects have been quantitatively determined to be due mainly to the different sensitivity of the sodium channels to pyrethroids and the negative temperature dependence of pyrethroid action on the sodium channels. The degradation of pyrethroids play only a minor role. The negative temperature dependence of pyrethroid action is due to the increased sodium current flow at low temperature. The major site of action of dieldrin and hexachlorocyclohexane is the GABA(A) receptor chloride channel complex. Dieldrin exerts a dual action, initial stimulation and subsequent suppression, and the latter is responsible for hyperexcitation of animals. Dieldrin stimulation requires the gamma2s subunit in the GABA receptor, whereas dieldrin suppression occurs in the presence or absence of the gamma2s subunit.
Assuntos
Inseticidas/toxicidade , Canais Iônicos/efeitos dos fármacos , Animais , Antagonistas de Receptores de GABA-A , Piretrinas/toxicidade , Ratos , Receptores de GABA-A/efeitos dos fármacosRESUMO
In steady state, the Ca content of the sarcoplasmic reticulum (SR) of cardiac myocytes is determined by a balance among influx and efflux pathways. The SR Ca content may be limited mainly by the ATP-supplied chemical potential that is inherent in the gradient between SR and cytosol. That is, forward Ca pumping from cytosol to SR may be opposed by energetically conservative reverse pumping dependent on intra-SR free [Ca]. On the other hand, SR Ca loading may be limited by dissipative pathways (pump slippage and/or pump-independent leak). To assess how SR Ca content is limited, we loaded voltage-clamped ferret ventricular myocytes cumulatively with known amounts of Ca via L-type Ca channels (ICa), using Na-free solutions to prevent Na/Ca exchange. We then measured the maximal resulting caffeine-released SR Ca content under control conditions, as well as when SR Ca pumping was accelerated by isoproterenol (1 micro M) or slowed by thapsigargin (0.2-0.4 micro M). Under control conditions, SR Ca content reached a limit of 137 micro mol.liter cytosol-1 (nonmitochondrial volume) when measured by integrating caffeine-induced Na/Ca exchange currents lintegraINaCaXdt) and of 119 micro mol.liter cytosol-1 when measured using fluorescence signals dependent on changes in cytosolic free Ca ([Ca]i). When Ca-ATPase pumping rate was slowed 39% by thapsigargin, the maximal SR Ca content decreased by 5 (integralINaCaXdt method) or 23% (fluorescence method); when pumping rate was increased 74% by isoproterenol, SR Ca content increased by 10% (fluorescence method) or 20% (integralINaCaXdt method). The relative stability of the SR Ca load suggests that dissipative losses have only a minor influence in setting the SR Ca content. Indeed, it appears that the SR Ca pump in intact cells can generate a [Ca] gradient approaching the thermodynamic limit.
Assuntos
Cálcio/metabolismo , Cardiotônicos/farmacologia , Isoproterenol/farmacologia , Miocárdio/metabolismo , Retículo Sarcoplasmático/efeitos dos fármacos , Retículo Sarcoplasmático/metabolismo , Tapsigargina/farmacologia , Animais , ATPases Transportadoras de Cálcio/efeitos dos fármacos , ATPases Transportadoras de Cálcio/metabolismo , Furões , Ventrículos do Coração , Homeostase/fisiologia , Miocárdio/citologiaRESUMO
Left ventricular hypertrophy (approximately 40%) was induced in rats by banding of the abdominal aorta. After 16 wk, ventricular homogenates were prepared for biochemical measurements and ventricular myocytes were isolated for functional studies. In myocytes, the effects of banding on intracellular Ca handling, contraction, and excitation-contraction (E-C) coupling were determined using indo 1 fluorescence and whole cell voltage clamp. After steady-state field or voltage-clamp stimulation to load the sarcoplasmic reticulum (SR), SR Ca content assessed by caffeine-induced Ca transients was the same in sham and banded groups. Despite this, cell shortening amplitudes were significantly depressed in the banded group, suggesting altered contractile properties. In banded rats, the SR Ca-adenosinetriphosphatase (Ca-ATPase) mRNA level was reduced, as was homogenate thapsigargin-sensitive SR Ca-ATPase, but cytosolic free Ca concentration ([Ca]i) decline attributed to SR Ca-ATPase activity in intact cells was not slowed. Banding also reduced Na/Ca exchange mRNA level but did not affect either Na-dependent sarcolemmal 45Ca transport in homogenate or the rate of [Ca]i decline in intact cells attributed to Na/Ca exchange (during caffeine-induced contractures). Banding also did not change the rate of [Ca]i decline mediated by the combined function of the mitochondrial Ca uptake and sarcolemmal Ca-ATPase in intact cells. Ca current (ICa) density and voltage dependence were the same in sham and banded groups. Ryanodine receptor mRNA, protein content, and ryanodine affinity were also unchanged in the banded group. At 1 mM extracellular Ca concentration ([Ca]o), banding did not affect E-C coupling efficacy in intact cells under voltage clamp (i.e., same contraction for given ICa and SR Ca load). However, when [Ca]o was reduced to 0.5 mM, the efficacy of E-C coupling was greatly depressed in the banded group (even though ICa and SR Ca content were matched). In summary, unloaded myocyte contraction was depressed in these hypertrophic hearts, but Ca transport was little altered, at 1 mM [Ca]o. However, reduction of [Ca]o to 0.5 mM appears to unmask a depressed fractional SR Ca release in response to a given ICa trigger and SR Ca load.
Assuntos
Cálcio/metabolismo , Cardiomegalia/fisiopatologia , Contração Miocárdica/fisiologia , Miocárdio/metabolismo , Função Ventricular/fisiologia , Animais , ATPases Transportadoras de Cálcio/metabolismo , Cardiomegalia/metabolismo , Cardiomegalia/patologia , Estimulação Elétrica , Hemodinâmica/fisiologia , Masculino , Miocárdio/patologia , Técnicas de Patch-Clamp , RNA Mensageiro/metabolismo , Ratos , Ratos Sprague-Dawley , Rianodina/metabolismo , Trocador de Sódio e Cálcio/metabolismoAssuntos
ATPases Transportadoras de Cálcio/metabolismo , Cálcio/metabolismo , Coração/fisiologia , Retículo Sarcoplasmático/metabolismo , Animais , Permeabilidade da Membrana Celular , Citosol/metabolismo , Técnicas In Vitro , Modelos Cardiovasculares , Técnicas de Patch-Clamp , Canal de Liberação de Cálcio do Receptor de Rianodina/fisiologiaRESUMO
Alterations in cellular Ca2+ transport and excitation-contraction coupling may contribute to dysfunction in cardiac hypertrophy. Left ventricular myocytes were isolated from rat hearts after 15-18 wk of suprarenal abdominal aortic banding to evaluate the hypothesis that hypertrophy alters the relationship between Ca2+ current (ICa) and sarcoplasmic reticulum (SR) Ca2+ load during steady-state voltage-clamp depolarization. Mean arterial pressure (MAP) and heart weight-to-body weight ratio of banded (B) animals were significantly higher than in control or sham-operated animals (C). Isolated myocyte dimensions and volume increased in parallel with whole heart hypertrophy and elevation in MAP. However, the relationship between membrane surface area (measured by capacitance) and cell volume (measured by laser scanning confocal microscopy) was unaltered (C: 8.9 +/- 0.3; B: 8.5 +/- 0.4 pF/pl). No differences in the voltage dependence of ICa activation, steady-state inactivation, or recovery from inactivation were detected between C and B myocytes. Maximal ICa density for the two groups was also not different either under basal conditions (C: 4.28 +/- 0.98; B: 4.57 +/- 0.60 pA/pF) or in the presence of 1 microM isoproterenol (C: 16.6 +/- 2.3; B: 16.5 +/- 2.3 pA/pF). The fraction of Ca2+ released from the SR by a single twitch was 55.4 +/- 9.4% in C and 37.1 +/- 6.9% in B (not significantly different). Steady-state Ca2+ influx during a twitch was calculated in units of micromoles per liter of nonmitochondrial volume from the integral of ICa (C: 13.4 +/- 0.7 microM; B: 13.3 +/- 0.8 microM). The SR Ca2+ load was similarly calculated by integration of Na+/Ca2+ exchange current induced by rapid caffeine application (C: 140 +/- 9 microM; B: 169 +/- 18 microM). We conclude that significant cellular hypertrophy is associated with proportional increases in sarcolemmal ICa influx, SR Ca2+ loading, and the amount of SR Ca2+ released in this model of pressure overload.
Assuntos
Cálcio/metabolismo , Hipertrofia Ventricular Esquerda/fisiopatologia , Miocárdio/patologia , Animais , Estenose da Valva Aórtica , Pressão Sanguínea , Condutividade Elétrica , Hemodinâmica , Hipertrofia Ventricular Esquerda/patologia , Masculino , Ratos , Ratos Sprague-Dawley , Retículo Sarcoplasmático/metabolismo , Fatores de TempoRESUMO
1. The effect of Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) on excitation-contraction coupling (E-C coupling) was studied in intact ferret cardiac myocytes using the selective inhibitor KN-93, KN-93 decreased steady-state (SS) twitch [Ca2+]i (by 51%), resting Ca2+ spark frequency (by 88%) and SS sarcoplasmic reticulum (SR) Ca2+ content evaluated by eaffeine application (by 37.5%). 2. Increasing extracellular Ca2+ concentration ([Ca2+]o) to 5 mM in KN-93 restored SR Ca2+ load and Ca2+ spark frequency towards that in control (2 mM Ca2+o), but SS twitch [Ca2+]i was still significantly depressed by KN-93. 3. KN-93 decreased Ca2+ transient amplitude of SS twitches much more strongly than the amplitude of post-rest (PR) twitches. In the control, the time constant (Tau) of [Ca2+]i decline of SS twitches was faster than that for PR twitches. This stimulation-dependent acceleration of [Ca2+]i decline was abolished by KN-93. 4. Voltage-clamp experiments demonstrated that KN-93 significantly inhibited sarcolemmal L-type Ca2+ current (ICa) during repetitive pulses by slowing recovery from inactivation. This may explain the preferential action of KN-93 to suppress SS vs. PR twitches. 5. In KN-93, even when both ICa and SR Ca2+ load were matched to the control levels by manipulation of conditioning voltage-clamp pulses, contraction and twitch Ca2+ transients were still both significantly depressed (to 39 and 49% of control, respectively). 6. Since KN-93 reduced SR Ca2+ release channel (RyR) activity during E-C coupling, even for matched SR Ca2+ load and trigger ICa, we infer that endogenous CaMKII is an important modulator of E-C coupling in intact cardiac myocytes. Effects of KN-93 on ICa and SS twitch [Ca2+]i decline also indicate that endogenous CaMKII may have stimulatory effects on ICa and SR Ca2+ uptake.
Assuntos
Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Contração Miocárdica , Miocárdio/enzimologia , Animais , Benzilaminas/farmacologia , Cafeína/farmacologia , Cálcio/metabolismo , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina , Proteínas Quinases Dependentes de Cálcio-Calmodulina/antagonistas & inibidores , Estimulantes do Sistema Nervoso Central/farmacologia , Diástole , Inibidores Enzimáticos/farmacologia , Furões , Coração/efeitos dos fármacos , Masculino , Retículo Sarcoplasmático/efeitos dos fármacos , Retículo Sarcoplasmático/metabolismo , Sulfonamidas/farmacologiaRESUMO
1. Fundamental properties of Ca2+ channel currents in rat and rabbit ventricular myocytes were measured using whole cell voltage clamp. 2. In rat, as compared with rabbit myocytes, Ca2+ channel current (ICa) was half-activated at about 10 mV more negative potential, decayed slower, was half-inactivated (in steady state) at about 5 mV more positive potential, and recovered faster from inactivation. 3. These features result in a larger steady-state window current in rat, and also suggest that under comparable voltage clamp conditions, including action potential (AP) clamp, more Ca2+ influx would be expected in rat myocytes. 4. Ca2+ channel current carried by Na+ and Cs+ in the absence of divalent ions (Ins) also activated at more negative potential and decayed more slowly in rat. 5. The reversal potential for Ins was 6 mV more positive in rabbit, consistent with a larger permeability ratio (PNa/PCs) in rabbit than in rat. ICa also reversed at slightly more positive potentials in rabbit (such that PCa/PCs might also be higher). 6. Ca2+ influx was calculated by integration of ICa evoked by voltage clamp pulses (either square pulses or pulses based on recorded rabbit or rat APs). For a given clamp waveform, the Ca2+ influx was up to 25% greater in rat, as predicted from the fundamental properties of ICa and Ins. 7. However, the longer duration of the AP in rabbit myocytes compensated for the difference in influx, such that the integrated Ca2+ influx via ICa in response to the species-appropriate waveform was about twice as large as that seen in rat.
Assuntos
Canais de Cálcio/metabolismo , Miocárdio/metabolismo , Sarcolema/metabolismo , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Animais , Cádmio/farmacologia , Bloqueadores dos Canais de Cálcio/farmacologia , Canais de Cálcio/efeitos dos fármacos , Eletrofisiologia , Técnicas In Vitro , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Miocárdio/citologia , Miocárdio/ultraestrutura , Nifedipino/farmacologia , Técnicas de Patch-Clamp , Coelhos , Ratos , Sarcolema/ultraestrutura , Canais de Sódio/efeitos dos fármacos , Canais de Sódio/metabolismo , Especificidade da EspécieRESUMO
OBJECTIVE: To ascertain the prevalence of and risk factors for long-term sequelae from acute Lyme disease. DESIGN: Population-based, retrospective cohort study. SETTING: A coastal region endemic for Lyme disease. PARTICIPANTS: Patients with a history of Lyme disease who were previously treated with antibiotics were compared with randomly selected controls. MEASUREMENTS: A standardized physical examination, health status measure (Short Form 36), psychometric test battery, and serologic analysis. RESULTS: Compared with the control group (n = 43), the Lyme group (n = 38; mean duration from disease onset to study evaluation, 6.2 years) had more arthralgias (61% compared with 16%; P < 0.0001); distal paresthesias (16% compared with 2%; P = 0.03); concentration difficulties (16% compared with 2%; P = 0.03); and fatigue (26% compared with 9%; P = 0.04), and they had poorer global health status scores (P = 0.04). The Lyme group also had more abnormal joints (P = 0.02) and more verbal memory deficits (P = 0.01) than did the control group. Overall, 13 patients (34%; 95% CI, 19% to 49%) had long-term sequelae from Lyme disease (arthritis or recurrent arthralgias [n = 6], neurocognitive impairment [n = 4], and neuropathy or myelopathy [n = 3]). Compared with controls, patients who had long-term sequelae had higher IgG antibody titers to the spirochete (P = 0.03) and received treatment later (34.5 months compared with 2.7 months; P < 0.0001). CONCLUSIONS: Persons with a history of Lyme disease have more musculoskeletal impairment and a higher prevalence of verbal memory impairment when compared with those without a history of Lyme disease. Our findings suggest that disseminated Lyme disease may be associated with long-term morbidity.
Assuntos
Doença de Lyme/complicações , Transtornos Mentais/etiologia , Doenças Musculoesqueléticas/etiologia , Doenças do Sistema Nervoso/etiologia , Estudos de Coortes , Feminino , Nível de Saúde , Humanos , Modelos Logísticos , Doença de Lyme/sangue , Doença de Lyme/psicologia , Masculino , Pessoa de Meia-Idade , Exame Físico , Psicometria , Estudos Retrospectivos , Fatores de Risco , Coloração pela Prata , Inquéritos e Questionários , Fatores de TempoRESUMO
A variety of marine neurotoxins exert potent and specific actions on neuronal sodium channels. Tetrodotoxin and saxitoxin block the sodium channel selectively without any effect on other types of voltage-activated and transmitter-activated ion channels. They bind to a site near the external orifice of the sodium channel on a one-to-one stoichiometric basis. The block is influenced by the membrane potential in a complex manner, and binding and penetration of calcium ions to the sodium channel appear to be responsible for the voltage-dependent block. Owing to the potent and specific sodium channel blocking action, tetrodotoxin and saxitoxin have been used extensively in various studies of ion channels. The dorsal root ganglion neurons of the rat are endowed with tetrodotoxin-sensitive and tetrodotoxin-resistant sodium channels. The latter is also resistant to saxitoxin. These two types of sodium channels exhibit different physiological and pharmacological profiles. Tetrodotoxin-resistant sodium channels are slower in time course and open and inactivate at less negative membrane potentials than tetrodotoxin-sensitive sodium channels. Lidocaine blocks tetrodotoxin-sensitive sodium channels more potently than tetrodotoxin-resistant sodium channels. However, Pb2+ and Cd2+ block tetrodotoxin-resistant channels more strongly. The pyrethroid insecticide allethrin modifies tetrodotoxin-resistant sodium channels while affecting tetrodotoxin-sensitive sodium channels to a much lesser extent. The differences in pharmacological and toxicological profiles between the two types of sodium channels are deemed critically important in understanding the mechanisms of action of various chemicals in animals.
Assuntos
Neurotoxinas/farmacologia , Saxitoxina/farmacologia , Canais de Sódio/efeitos dos fármacos , Tetrodotoxina/farmacologia , Animais , Humanos , Técnicas de Patch-ClampRESUMO
The pyrethroid insecticides are known to modify neuronal sodium channels to cause a prolongation of whole cell current. The sodium channels expressed in the dorsal root ganglion neurons of the rat are of two types, one highly sensitive to tetrodotoxin and the other highly resistant to tetrodotoxin. The pyrethroid allethrin exerted profound effects on tetrodotoxin-resistant sodium channels while causing minimal effects on tetrodotoxin-sensitive sodium channels. Currents derived from tetrodotoxin-resistant sodium channels were greatly prolonged during a step depolarization; the tail currents upon repolarization were also augmented and prolonged. In the tetrodotoxin-sensitive sodium channel currents, these changes caused by allethrin were much smaller or negligible. The activation and inactivation voltages of tetrodotoxin-resistant peak sodium currents were not significantly altered by allethrin. The differential action of allethrin on the two types of sodium channels would be important not only in identifying the target molecular structure but also in interpreting the symptoms of poisoning in mammals.
Assuntos
Aletrinas/farmacologia , Gânglios Espinais/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Canais de Sódio/efeitos dos fármacos , Tetrodotoxina/farmacologia , Animais , Resistência a Medicamentos/fisiologia , Gânglios Espinais/citologia , RatosRESUMO
The symptoms of poisoning by the pyrethroid and cyclodiene insecticides are characterized by hyperexcitation and convulsions followed by paralysis. The main target site of the pyrethroids has been identified to be the sodium channels which are kept open for unusually long periods of time, causing a prolonged sodium current to flow which, in turn, leads to hyperexcitation of the nervous system. We have now found large differential sensitivity to the pyrethroids in two types of sodium channels. The dorsal root ganglion neurons of the rat were endowed with two types of sodium channels, one sensitive to the blocking action of tetrodotoxin (TTX) and the other insensitive to TTX. The type I pyrethroid allethrin and the type II pyrethroid deltamethrin were both effective in prolonging the sodium current in the TXX-resistant sodium channel but had only a small effect on the TTX-sensitive sodium channel. These two types of sodium channels also exhibited marked differences in their physiological properties, including the time course of current, the activation voltage, and the steady-state inactivation. In contrast to the pyrethroids, lindane and the cyclodienes endrin, isobenzan, dieldrin and heptachlor-epoxide suppressed the GABA-induced chloride current. The initial transient component of the chloride current was blocked more than the late sustained component. The suppression of the GABA-mediated synaptic inhibition would cause hyperexcitation of the nervous system. The results are compatible with the convulsant action of these insecticides.
Assuntos
Dieldrin/toxicidade , Endrin/toxicidade , Proteínas de Membrana/efeitos dos fármacos , Piretrinas/toxicidade , Receptores de GABA-A/efeitos dos fármacos , Canais de Sódio/efeitos dos fármacos , Animais , Canais de Cloreto , Hexaclorocicloexano/toxicidade , Humanos , Tetrodotoxina/farmacologiaRESUMO
OBJECTIVE: To determine whether the presence of anticardiolipin antibodies is a risk factor for ischemic stroke and venous thrombosis in healthy adult men. DESIGN: A nested, case-control study in a prospective cohort. SETTING: A nationwide study of physicians. PARTICIPANTS: The study sample was drawn from the Physicians' Health Study, a randomized, double-blind, placebo-controlled trial of aspirin and beta-carotene in 22,071 male physicians. At entry, 68% of the participants submitted plasma samples that were subsequently frozen at -80 degrees C. During 60.2 months of follow-up, follow-up for nonfatal outcomes was 99.7% complete and ascertainment of fatal outcomes was 100% complete. We identified men with documented ischemic stroke, deep venous thrombosis of the leg, or pulmonary embolus and for whom a plasma sample was available. A control was matched by age, smoking history, and length of follow-up to each of the 100 patients with ischemic stroke and the 90 patients with deep venous thrombosis or pulmonary embolus. MEASUREMENTS: Plasma samples were assessed for IgG anticardiolipin antibodies by enzyme-linked immunosorbent assay. The mean anticardiolipin antibody titers of the case patients in the two diagnostic groups (ischemic stroke; venous thrombosis or pulmonary embolus) were compared with those of the control groups, and relative risks were calculated for patients in increasing percentile categories of anticardiolipin antibodies by conditional logistic regression. RESULTS: The anticardiolipin antibody titers were higher in case patients with deep venous thrombosis and pulmonary embolus than in their matched controls (P = 0.01). Persons with anticardiolipin antibody titers above the 95th percentile had a relative risk for developing deep venous thrombosis or pulmonary embolus of 5.3 (95% CI, 1.55 to 18.3; P = 0.01). The anticardiolipin antibody titers in case patients with ischemic stroke and controls were not significantly different (P > 0.2), and no clear trend of higher risks among those with elevated levels of anticardiolipin antibodies was observed. CONCLUSION: An anticardiolipin antibody level above the 95th percentile is an important risk factor for deep venous thrombosis or pulmonary embolus but not for ischemic stroke in healthy adult men.
Assuntos
Anticorpos Anticardiolipina/sangue , Isquemia Encefálica/imunologia , Embolia Pulmonar/imunologia , Tromboflebite/imunologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Estudos de Casos e Controles , Ensaio de Imunoadsorção Enzimática , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Fatores de Risco , Estatística como AssuntoRESUMO
Excitable tissues have been reported to respond to weak microwave (MW) fields, possibly by nonlinear perturbation of a cellular process such as ion conduction across membranes. We sought effects of MW (continuous wave, 2.45 GHz, specific absorption rates 12.5 or 125 mW/g) on input resistances and action potential (AP) intervals of neurons in ganglia of snails (Helix aspersa), at 20.9 +/- 0.1 degrees C. At 12.5 mW/g, input resistance did not change during irradiation, but increased (p < 0.05) afterward. At 125 mW/g, input resistance during irradiation was lower than in unirradiated controls. Serial correlograms changed marginally more frequently in MW experiments than in controls, but the changes had no consistent pattern. The AP firing rate was affected by MW, but the direction was not consistent across cells. When AP generation was modeled as being due to a neuronal input current, MW did not affect its mean, standard deviation, or autocorrelation. Unlike MW, temperature changes caused neurons to respond robustly and reversibly. Threshold for changing input resistance was 0.63 degree C. The data suggest that MW may enhance degenerative effects such as metabolic rundown or loss of ion channel patency, but do not indicate a specific mechanism for MW interaction with neurons.
Assuntos
Micro-Ondas , Neurônios/fisiologia , Potenciais de Ação/efeitos da radiação , Animais , Caracois Helix , Canais Iônicos/fisiologia , MicroeletrodosRESUMO
OBJECTIVE: To investigate the prevalence of cognitive dysfunction in randomly selected patients with systemic lupus erythematosus (SLE). METHODS: Randomly selected, ambulatory patients with SLE (n = 49) or with rheumatoid arthritis (RA) (n = 40) completed neuropsychological tests. These included Associate Learning, Switching Attention, Continuous Performance, Associate Recall, Hand-Eye Coordination, Pattern Comparison, Pattern Memory, the Stroop Color and Word Test, and the Symptoms Checklist-90R. Results were evaluated by multiple linear regression analysis. RESULTS: SLE patients had poorer performance than RA patients on the test of attention (P = 0.002) and tests of visuospatial ability (P = 0.03) and P = 0.04), independent of age, education, or steroid use. The conservative level of statistical significance, adjusting for multiple comparisons, was 0.005. SLE patients reported more symptoms of cognitive difficulty. CONCLUSION: Cognitive dysfunction is common in ambulatory SLE patients as measured by standardized tests and is a cause of distress and impaired functioning. Self-reported cognitive difficulty appears to correlate with objective performance.
Assuntos
Artrite Reumatoide/complicações , Transtornos Cognitivos/epidemiologia , Lúpus Eritematoso Sistêmico/complicações , Adulto , Transtornos Cognitivos/diagnóstico , Transtornos Cognitivos/etiologia , Feminino , Humanos , Análise dos Mínimos Quadrados , Modelos Lineares , Masculino , Pessoa de Meia-Idade , Testes Neuropsicológicos , Prevalência , Distribuição Aleatória , Análise de RegressãoRESUMO
OBJECTIVE: To determine the prevalence of genitourinary mycoplasma infection in women with systemic lupus erythematosus (SLE). METHODS: Urine specimens from 49 patients with SLE and 22 patients with chronic fatigue syndrome (CFS) were cultured for mycoplasma. Patient records were reviewed for medical history and SLE disease activity. RESULTS: Sixty-three percent of the SLE patients were culture positive, compared with 4.5% of the CFS patients (P less than 0.001). Neither corticosteroid treatment, SLE activity, nor age accounted for this difference. CONCLUSION: Genitourinary mycoplasma colonization occurs significantly more frequently in SLE than in CFS.