[Traffic medicine in rehabilitation]. / Verkehrsmedizin in der Rehabilitation.

Participation in road traffic in Germany is governed by various laws and acts. Physicians are obliged to decide whether, in the presence of medical conditions and handicaps, a patient is fit to drive a car safely. Following myocardial infarction this decision is generally made by specialized cardiologists (specialization in social medicine) in rehabilitation centers. If a patient does not undergo rehabilitation after an acute event, this decision must be made by the invasive cardiologist, who is often not skilled in this kind of assessment. The second problem faced in Germany is the discrepancy between outdated legal regulations, modern cardiology and the current standard of medical knowledge, especially in terms of treatment for acute coronary syndrome. According to current legal regulations, no patient at all is allowed to drive a car in Germany after any form of myocardial infarction, regardless of ejection fraction, for at least 3 months. In contrast, a working group for the German Society of Cardiology published a position paper in 2010 in which patients could be allowed to drive a car 2 weeks after an AMI with an EF >30. The third problem in this context in Germany is that, due to a decision by the Federal High Court of Justice, physicians are not only responsible to inform the patient, if he is not allowed to drive a car, but also have to assure that he does not leave the hospital or practice by car, if he is not allowed to. If the patient however opposes, drives home and has an accident, the physician is liable for the damages. The fourth and final problem lies in the fact that most cardiologists in Germany are neither skilled in legal traffic assessment, nor are they familiar with this field and its problems.

Testosterone modulates cardiomyocyte Ca(2+) handling and contractile function.

The extent to which sex differences in cardiac function may be attributed to the direct myocardial influence of testosterone is unclear. In this study the effects of gonadal testosterone withdrawal (GDX) and replacement (GDX+T) in rats, on cardiomyocyte shortening and intracellular Ca(2+) handling was investigated (0.5 Hz, 25 oC). At all extracellular [Ca(2+)] tested (0.5-2.0 mM), the Ca(2+) transient amplitude was significantly reduced (by approximately 50 %) in myocytes of GDX rats two weeks post-gonadectomy. The time course of Ca(2+) transient decay was significantly prolonged in GDX myocytes (tau, 455+/-80 ms) compared with intact (279+/-23 ms) and GDX+T (277+/-19 ms). Maximum shortening of GDX myocytes was markedly reduced (by more than 60 %) and relaxation significantly delayed (by more than 35 %) compared with intact and GDX+T groups. Thus testosterone replacement completely reversed the cardiomyocyte hypocontractility induced by gonadectomy. These results provide direct evidence for a role of testosterone in regulating functional Ca(2+) handling and contractility in the heart.

[Preoperative coagulation screening prior to adenoidectomy and tonsillectomy]. / Präoperatives Screening auf Gerinnungsstörungen vor Adenotomie und Tonsillektomie.

BACKGROUND: Laboratory tests are widely used to screen children with planned surgery to detect unknown coagulation defects. This study investigates the predictive value of commonly used coagulation tests (thromboplastin time, partial thromboplastin time and thrombocyte count) compared with a standardized bleeding history. PATIENTS: In 702 patients 500 adenoidectomies and 500 tonsillectomies were done, results of laboratory evaluation and individual bleeding history were evaluated. RESULTS: 9.4 % of all laboratory tests showed abnormal results. 30.5 % of the children awaiting adenoidectomy had a suspicious bleeding history as had 22 % of patients undergoing tonsillectomy. In the clinical course of adenoidectomy no bleeding occurred. After tonsillectomy 15 children (3 %) showed moderate, 12 patients (2.4 %) severe postoperative bleeding. The positive predictive value of coagulation screening reached 6.8 % whereas history alone predicted 9.2 % of observed post tonsillectomy bleeding. CONCLUSIONS: The results of this study demonstrate the lacking effect of laboratory tests to predict postoperative bleeding complications. Taking a careful history of bleeding risks and testing only patients with suspicious history reduces the risk of bleeding more effective. Counseling about bleeding symptoms and postoperative survey of patients are additional measures which may protect the children.

Effects of gender on intracellular.

The present study investigated the effects of gender on intracellular [Ca2+] ([Ca2+]i) in freshly isolated rat cardiac myocytes. Changes in [Ca2+]i in response to varied extracellular [Ca2+], different stimulus frequencies and addition of caffeine and isoprenaline were monitored using fura-2 in both male and female cardiac myocytes. Increasing extracellular [Ca2+] and stimulus frequency resulted in significant increases in peak [Ca2+] and the amplitude of the Ca2+ transient in both male and female cardiac myocytes. However, as extracellular [Ca2+] was raised, peak [Ca2+] and the amplitude of the Ca2+ transient increased significantly more in male than female cardiac myocytes. In addition a significant difference between male and female cells at each stimulus frequency was apparent. The time course of decay of the Ca2+ transient was significantly slower in female cardiac myocytes when compared with male cardiac myocytes, along with significantly slowed times to peak shortening and 50% relaxation, and a reduced extent of shortening. There was no significant difference in the amplitude of caffeine-induced [Ca2+]i responses between male and female cells, however, [Ca2+]i increased more readily in male cells than in female cells when isoprenaline was added. The data demonstrate that, under a variety of conditions, intracellular [Ca2+] rises to higher levels in cardiac myocytes from male as compared to female rats.

Stimulus interval-dependent differences in Ca2+ transients and contractile responses of diabetic rat cardiomyocytes.

OBJECTIVE: The aim of this study was to gain further insights into the consequences of insulin-dependent diabetes mellitus on cardiomyocyte calcium handling. METHODS: The effects of steady state and transient changes in stimulus frequency on the intracellular Ca2+ transient and cell shortening were examined in left ventricular cardiomyocytes isolated from the hearts of control and streptozotocin-induced diabetic rats. RESULTS: During steady state stimulation diabetic rat cardiomyocytes displayed a slower decay of the Ca2+ transient and longer times for maximum cell shortening and re-lengthening. At 1.5 mM extracellular [Ca2+], increasing stimulus frequency over the range 0.2-1.0 Hz led to an increase in resting and peak [Ca2+]i as well as the amplitude of the transient in both the control and diabetic groups. At frequencies greater than 0.4 Hz the amplitude of the transient was significantly depressed in diabetic rat cells and this was not normalized by increasing extracellular [Ca2+] to 2.5 mM. Recovery of sarcoplasmic reticulum (SR) Ca2+ release was measured from the time course of restitution of the intracellular Ca2+ transient. In both control and diabetic rat cardiomyocytes recovery of the transient occurred in two phases. In diabetic rat myocytes, the initial rapid phase of restitution at intervals <1 s was markedly slowed. The fraction of Ca2+ recirculating between the SR and the cytosol was estimated from the decline in amplitude of transients following post-rest potentiation. There was no difference in this fraction between control and diabetic rat cells either at 1.5 or 2.5 mM extracellular [Ca2+]. CONCLUSION: The blunted frequency response of diabetic rat cardiomyocytes at frequencies greater than 0.4 Hz is consistent with reduced SR Ca2+ uptake leading to reduced SR Ca2+ content and subsequent release. At stimulus intervals greater than 1 Hz this is likely to be exacerbated by slower recovery of SR Ca2+ release. Despite the evidence for depressed SR Ca2+ uptake, the relative amount of Ca2+ recirculating within diabetic rat cardiomyocytes remains unaltered. This is most likely due to an accompanying reduction in Ca2+ efflux from the cell due either to depressed Na+/Ca2+ exchanger activity, or an elevation in intracellular Na+ levels.

Effects of anoxia on force, intracellular calcium and lactate production of urinary bladder smooth muscle from control and diabetic rats.

PURPOSE: To examine the effects of inhibiting oxidative metabolism on lactate production (J(Lac)), force and [Ca2+]i in longitudinal smooth muscle from urinary bladders of control and diabetic rats. MATERIALS AND METHODS: Strips of longitudinal smooth muscle were isolated from urinary bladders of diabetic rats and their age-matched controls. Force and [Ca2+]i were measured simultaneously in muscle strips loaded with the calcium indicator, fura-2. Separate muscle strips were used to determine J(Lac) by standard enzymatic assay. The muscles were stimulated to contract with 65 mM K+ or 1 microM carbachol (CCh) in the presence of 2.5 mM Ca2+ and either 5, 10 or 25 mM glucose. Oxidative metabolism was inhibited either by replacing O2 in solution with N2, or by addition of 2 mM NaCN. RESULTS: J(Lac) was significantly less in diabetic muscles than control muscles under both normoxic and anoxic conditions. During stimulation under anoxic conditions, the diabetic muscles were less able to maintain force than the controls. Despite a marked decline in force in both diabetic and control muscles under anoxic conditions, [Ca2+]i remained elevated to levels that were in fact higher than those observed during stimulation under normoxic conditions. Increasing the glucose concentration had no significant effect during normoxia, however, under anoxic conditions, the higher concentration improved force maintenance in both control and diabetic muscles. There were no apparent effects of the glucose concentration on [Ca2+]i in either diabetic or control muscles. CONCLUSION: The results reveal that urinary bladder smooth muscle from diabetic rats has a reduced ability to maintain contraction under anoxic conditions. This most likely reflects a greater energy limitation as evidenced by the reduced J(Lac) in diabetic muscles. In both diabetic and control muscles there was a marked dissociation between force and [Ca2+]i when oxidative metabolism was inhibited. This may indicate preferential use of glycolytically produced ATP for maintenance of [Ca2+]i homeostasis under these conditions.

Long-term morbidity following axillary dissection in breast cancer patients--clinical assessment, significance for life quality and the impact of demographic, oncologic and therapeutic factors.

OBJECTIVE: This study describes in detail the surgery-related symptoms following axillary lymph node dissection in breast cancer patients and considers both their significance for long term quality of life and the impact of possible influencing factors. MATERIAL AND METHODS: Three hundred and ninety six patients were studied retrospectively using a self-report questionnaire and a clinical examination. The symptoms, numbness, pain, edema, arm strength and mobility were evaluated. The subjective assessment of the degree of symptom intensity was compared with objective measurements. The extent of surgery (number of resected nodes, level of dissection) as well as the influence of demographic, oncologic and adjuvant measures (age, time interval, number of involved nodes, chemotherapy) were evaluated. RESULTS: Shoulder-arm morbidity and fear of cancer recurrence were the most important long-term sources of distress following breast cancer surgery in our study population. Demographic, oncologic and therapeutic measures including the extent of surgery had no influence on long-term morbidity. The intensity of all evaluated symptoms was reported to be more severe in patients' subjective statements than in the results of clinical assessment. CONCLUSION: Shoulder-arm morbidity following axillary dissection is a frustrating polysymptomatic disease that seems to be relatively unaffected by therapeutic measures. The surgical trauma necessary for adequate tumor staging (removal of 10 lymph nodes) seems decisive for the postsurgery syndrome following axillary dissection. For node-positive patients complete axillary clearing may improve tumor control without worsening long-termmorbidity. New techniques, such as the sentinel-node-biopsy, that selects patients with negative axillary status while preserving the integrity of axillary structures, may improve the overall morbidity.

Effects of streptozotocin-induced diabetes mellitus on intracellular calcium and contraction of longitudinal smooth muscle from rat urinary bladder.

PURPOSE: To examine the effect of diabetes on [Ca2+]i and contractility in longitudinal smooth muscle of the urinary bladder. MATERIALS AND METHODS: Longitudinal smooth muscle strips were isolated from the urinary bladders of rats with STZ-induced diabetes as well as age matched controls. Force and [Ca2+]i were measured simultaneously in muscle strips loaded with the calcium indicator, fura-2. Contractions were initiated by electrical field stimulation (EFS) at various frequencies, as well as by high K+, carbachol (CCh) and cyclopiazonic acid (CPA) in the presence of varying concentrations of extracellular Ca2+. RESULTS: In unstimulated muscles, there was no significant difference in resting [Ca2+]i between the control and diabetic groups. However, the muscle strips from the diabetic animals produced higher force levels in response to EFS, high K+, CCh and CPA than those from control animals. The higher force development in the diabetic muscles was not associated with greater increases in [Ca2+]i, which in fact tended to be lower during stimulation in the diabetic tissues. When stimulated by CCh in the presence of nifedipine, both control and diabetic muscles exhibited a nifedipine-resistant component of contraction, however, this was significantly larger in the diabetic muscles. CONCLUSION: The results suggest that there are no major impairments in either intracellular calcium regulation or contractile function in bladder smooth muscle after 8-weeks of STZ-induced diabetes. However, a non-specific enhancement of force production was seen, which was not associated with increases in [Ca2+]i. These changes imply that the apparent sensitivity to [Ca2+]i is enhanced in bladder smooth muscle from diabetic rats.

Effects of pyruvate on intracellular Ca2+ regulation in cardiac myocytes from normal and diabetic rats.

1. Pyruvate has been shown to enhance the contractile performance of cardiac muscle when provided as an alternative substrate to glucose. The aims of the present study were to determine whether the inotropic effects of pyruvate are due to increased mobilization of intracellular Ca2+ ([Ca2+]i) and to compare the effects of pyruvate on [Ca2+]i levels in myocytes from normal and diabetic animals. 2. Fura-2 was used to monitor [Ca2+]i in ventricular myocytes isolated from control and streptozotocin-treated male Wistar rats. The experiments were performed at 25 degrees C, with an extracellular [Ca2+] of 1.5 mmol/L and either 10 mmol/L glucose or 10 mmol/L pyruvate as the substrate. 3. In myocytes from both control and diabetic rats, increasing the stimulus frequency from 0.33 to 2.0 Hz resulted in significant increases in resting and peak [Ca2+]i as well as in the amplitude of the [Ca2+]i transient, irrespective of substrate. Compared with glucose, pyruvate significantly increased resting and peak [Ca2+]i and the amplitude of the [Ca2+]i transient at each stimulus frequency in myocytes from both control and diabetic animals. However, the extent of potentiation of the [Ca2+]i transient amplitude produced by pyruvate was significantly less in myocytes from the diabetic rats. 4. The rate of restitution of the [Ca2+]i transient was used as an index of the rate of Ca2+ cycling by the sarcoplasmic reticulum (SR). Pyruvate enhanced the rate of restitution in control but not diabetic rat cells. 5. The time course of decay of the [Ca2+]i transient was analysed as a measure of the rate of removal of Ca2+ from the cytosol. Pyruvate tended to increase the rate of decay in cells from control but not diabetic animals. The rate of decay was slower in cells from diabetic animals compared with controls. 6. The data reveal that pyruvate increases SR Ca2+ cycling, leading to greater Ca2+ release and an increase in the amplitude of the [Ca2+]i transient. Therefore, it seems highly likely that increased [Ca2+]i mobilization is responsible for the previously reported positive inotropic actions of pyruvate. These effects of pyruvate are attenuated in diabetic rat cells, which may reflect an impaired capacity of mitochondria in diabetic hearts to oxidize pyruvate, thus limiting potential energetic benefits.

Acute effects of taurine on intracellular calcium in normal and diabetic cardiac myocytes.

The present study investigated the acute effects of taurine on intracellular Ca2+ ([Ca2+]i) in normal and diabetic cardiac myocytes. [Ca2+]i was monitored using fura-2 in single myocytes isolated from control or streptozotocin-treated rats and paced at frequencies between 0.33 Hz and 2.0 Hz in the absence or presence of 20 mM taurine. Increasing stimulus frequency resulted in significant increases in resting and peak [Ca2+]i, and amplitude of the Ca2+ transient in both control and diabetic myocytes. The amplitude of the Ca2+ transient and the extent of its increase with increasing frequency was, however, significantly lower in the diabetic myocytes. Taurine significantly increased resting [Ca2+]i, peak [Ca2+]i, and the amplitude of the Ca2+ transient in both control and diabetic myocytes at all stimulus frequencies examined. The degree of potentiation of the Ca2+ transient decreased with increasing stimulus frequency in control cells but not in diabetic cells. In the absence of taurine the decay of the Ca2+ transient was significantly slower in diabetic than control myocytes. Taurine was without significant effect on the time course of the Ca2+ transient decay in control cells, however, in diabetic cells it significantly accelerated the rate of decay. The data demonstrate directly that taurine is able to increase [Ca2+]i and the amplitude of the Ca2+ transient in both normal and diabetic cardiac myocytes. In addition several of the effects of taurine appeared to be more pronounced in diabetic than control cells.

Intracellular Ca2+ and adrenergic responsiveness of cardiac myocytes in streptozotocin-induced diabetes.

1. The contractile function of diabetic hearts is impaired. In addition, the responsiveness of diabetic cardiac muscle to sympathetic stimulation is altered. Previous studies have revealed a depressed response to beta-adrenoceptor stimulation; however, the response to alpha-adrenoceptor activation remains controversial. Because alpha- and beta-adrenoceptor agonists increase cardiac contractility, largely through increased mobilization of intracellular Ca2+, the aim of the present study was to investigate the effects of alpha- and beta-adrenoceptor stimulation on intracellular Ca2+ handling in cardiac myocytes from streptozotocin-induced diabetic rats. 2. Intracellular Ca2+ was measured using fura-2. Under basal conditions (27 degrees C, 2.5 mmol/L extracellular [Ca2+], 0.3 Hz stimulation), there was no significant difference in resting or peak Ca2+ levels between control and diabetic cardiomyocytes. However, the time course of the intracellular Ca2+ transient was significantly prolonged in cells from diabetic hearts. 3. The beta-adrenoceptor agonist orciprenaline (at 10(-7) and 10(-6) mol/L) increased the amplitude of the Ca2+ transient in both groups; however, the extent of potentiation was less in diabetic compared with control cardiomyocytes. Orciprenaline decreased the duration of the transient to the same extent in both groups. 4. The alpha-adrenoceptor agonist phenylephrine (at 10(-7) and 10(-6) mol/L) had no effect on the Ca2+ transient in control myocytes but caused a significant concentration-dependent increase in its amplitude in diabetic cardiomyocytes. Phenylephrine had no effect on the time course of the transient in either group. 5. These results demonstrate differential effects of insulin-dependent diabetes on the responsiveness of cardiomyocytes to alpha- and beta-adrenoceptor stimulation. The heightened response to alpha-adrenoceptor stimulation observed in diabetic cardiomyocytes may partly compensate for the diminished myocardial beta-adrenoceptor response.

Force, membrane potential and cytoplasmic Ca2+ responses to cyclic nucleotides in rat anococcygeus muscle.

Simultaneous recordings of membrane potential and force, and cytoplasmic calcium ([Ca2+]i) and force were made in rat anococcygeus to determine whether membrane hyperpolarisation plays a role in cyclic nucleotide-induced relaxation. In the presence of phenylephrine (0.2 microM), which evoked sustained contraction, an elevation in [Ca2+]i, and depolarisation, nitroprusside (5 microM) caused 96+/-3% relaxation, 77+/-3% decrease in suprabasal [Ca2+]i, and 16+/-2 mV hyperpolarisation. Forskolin (1 microM) caused 98+/-1% relaxation, 92+/-2% decrease in suprabasal [Ca2+]i, and 18+/-1 mV hyperpolarisation. These responses persisted in the presence of a variety of K+ channel blockers or in ouabain. The decrease in [Ca2+]i preceded the commencement of relaxation whereas the onset of hyperpolarisation lagged behind. Thus, cyclic nucleotide-mediated relaxation in rat anococcygeus is not dependent on hyperpolarisation mediated by the opening of K+ channels. Rather, it is suggested that the decrease in [Ca2+]i gives rise to hyperpolarisation, which reflects a decline in the Ca2+ dependent conductance(s) activated by phenylephrine.

Force and intracellular Ca2+ during cyclic nucleotide-mediated relaxation of rat anococcygeus muscle and the effects of cyclopiazonic acid.

1. Simultaneous recordings of tension and [Ca2+]i were made in rat anococcygeus muscle strips to investigate possible mechanisms involved during cyclic nucleotide-mediated relaxation. Relaxation of pre-contracted muscles was induced by sodium nitroprusside (SNP) or forskolin and the effects of cyclopiazonic acid (CPA) on these responses were examined. 2. In muscles pre-contracted with 0.2 microM phenylephrine addition of SNP (10 microM) caused a rapid and near complete relaxation of force. This was accompanied by a decrease in [Ca2+]i, however, this was not of a comparable magnitude to the decrease in force. The level of [Ca2+]i in muscles relaxed with SNP was shown to be associated with substantially higher force levels in the absence of SNP. Forskolin (10 microM) caused a slower, essentially complete relaxation which was associated with a proportional decrease in [Ca2+]i. 3. In muscles pretreated with SNP or forskolin subsequent responses to phenylephrine were attenuated with both force and [Ca2+]i rising slowly to attain eventually levels similar to those observed when the relaxant was applied to pre-contracted muscles. 4. Exposure of the muscles to the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor, CPA (10 microM), resulted in a sustained increase in [Ca2+]i which, in most cases, was not associated with any force development. The relaxation and decrease in [Ca2+]i in response to both SNP and forskolin were attenuated and substantially slowed in the presence of CPA. Overall the extent of this attenuation was greater for SNP. For both SNP and forskolin, CPA attenuated the decrease in [Ca2+]i to a greater extent than the decrease in force. In some cases, SNP-mediated relaxation in the presence of CPA was observed with almost no detectable change in [Ca2+]i. 5. The results suggest that, in the rat anococcygeus muscle under normal circumstances, a lowering of [Ca2+]i can fully account for the relaxation induced by forskolin but not for that induced by SNP, where mechanisms independent of changes in [Ca2+]i appear to contribute. Whilst Ca2+ sequestration into the sarcoplasmic reticulum plays a role in the relaxation mediated by both SNP and forskolin other Ca2+ lowering mechanisms may also be involved, especially in the response to forskolin.

Force and intracellular Ca2+ during NANC-mediated relaxation of rat anococcygeus muscle and the effects of cyclopiazonic acid.

1. Simultaneous recordings of tension and [Ca2+]i during NANC-mediated relaxation were made in the rat anococcygeus muscle under various conditions. 2. In muscles precontracted with guanethidine, nitrergic stimulations at 2 Hz produced a rapid decrease in both the tension and [Ca2+]i. 3. The nitric oxide synthase inhibitor, NG-nitro-L-Arginine (NOLA, 100 mumol/L) completely abolished the decreases in the [Ca2+]i and force response of the NANC-mediated relaxation. 4. Noradrenergic-mediated contractions elicited by electrical field stimulation were potentiated by the addition of NOLA. In the absence of NOLA, the motor responses were larger in magnitude at 10 Hz stimulation than at 2 Hz. After NOLA, both the force response and the associated rise in [Ca2+]i were substantially increased in comparison to the control stimulations. Proportionately the potentiation of the 2 Hz response was of a far greater magnitude than that of the 10 Hz response. 5. The guanylate cyclase inhibitor methylene blue (10 mumol/L), partially inhibited the force and [Ca2+]i response of the NANC relaxation. 6. Following exposure of the muscles to the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor, cyclopiazonic acid, (10 mumol/L) the responses to NANC stimulation were inhibited. The attenuated relaxation response displayed a bi-phasic timecourse and the Ca2+ change in comparison to that of the control was markedly smaller. In some cases, a relaxation was observed with no detectable change in the [Ca2+]i. 7. The results suggest that part of the relaxation response observed with NANC-mediated relaxation in the rat anococcygeus is dependent on Ca2+ sequestration into the sarcoplasmic reticulum. However, other Ca2+ lowering mechanisms and possible Ca2+ independent mechanisms may also contribute to the NANC relaxation response.

Metabolism of toad ventricle during alterations to the inotropic state.

The heat produced by toad ventricle during manipulations of the inotropic state was measured using thermopiles, and some comparisons made to rat ventricle. The tension-independent heat, peak stress, and the tension-dependent heat increased when [Ca2+]o increased from 0.25 to 2 mM in Ringer. In 2 mM [Ca2+]o, tension-independent heat, peak stress, and tension-dependent heat were 3.1 +/- 0.4 mJ/g, 38.4 +/- 5.5 mN/mm2, and 0.49 +/- 0.06 units; about 25% of the tension-independent heat may relate to the Na(+)-K+ pump. At similar [Ca2+]o, rat ventricle produced a smaller tension-independent heat (1.6 +/- 0.2 mJ/g), and active heat per unit stress (0.22 +/- 0.01 units) than toad. Tension-independent heat, stress, and tension-dependent heat were increased by orciprenaline, and decreased by BDM. Ouabain increased the stress and tension-dependent heat but not the tension-independent heat. Five millimolar [Ca2+]o in HEPES buffer decreased the stress but increased the tension-dependent heat compared to 2 mM [Ca2+]o in Ringer. Ryanodine and CPA caused major reductions in force and tension-independent heat in rat, but had little effect on toad ventricle. In conclusion, our results suggest that in toad ventricle (a) the sarcoplasmic reticulum plays only a minor role in activation and relaxation, (b) the Na(+)-K+ pump contributes substantially to activation metabolism, (c) active metabolism is stimulated by increases in [Ca2+]o and (d) there is a larger tension-independent heat, a larger active metabolism per unit stress, and a lower basal metabolism than in rat papillary muscle. The energy cost of removing intracellular Ca2+ through the sarcolemma appears to be greater than uptake into sarcoplasmic reticulum.

Effects of cyclopiazonic acid on [Ca2+]i and contraction in rat urinary bladder smooth muscle.

Cyclopiazonic acid (CPA) has been reported to inhibit the Ca(2+)-ATPase of the sarcoplasmic reticulum (SR) in skeletal and smooth muscle. In the present study the effect of CPA on [Ca2+]i and force in rat urinary bladder smooth muscle was examined. The fluorescent Ca2+ indicator Fura-2 was used to monitor intracellular Ca2+, simultaneously with isometric force production. Addition of CPA to unstimulated muscles bathed in 2.5 mM Ca2+ containing Krebs solution resulted in a significant and sustained increase in [Ca2+]i from 99 +/- 7 to 273 +/- 51 nM. This increase in [Ca2+]i was dependent upon the presence of extracellular Ca2+ since when CPA was added to muscles in Ca(2+)-free media it produced only a small, transient increase in [Ca2+]i that was not sustained. Peak force levels produced by transmural stimulation, carbachol and high KCl solution were not altered by the presence of CPA, however, the increase in [Ca2+]i associated with these contractions was larger when CPA was present. In response to transmural stimulation, the times taken for both force and [Ca2+]i to rise to 50% of their peak values were attenuated in the presence of CPA. Conversely, there was no effect of CPA on the times taken for force or [Ca2+]i to fall to 50% of their stimulated values upon the cessation of stimulation. Under control conditions both carbachol and high KCl could initiate transient increases in [Ca2+]i and force in the absence of extracellular Ca2+. In the presence of CPA, the response to carbachol was virtually completely inhibited, however, the response to high KCl was only partially inhibited. The ability of CPA to inhibit the carbachol response in Ca(2+)-free media suggests that this response is due to release of Ca2+ from the SR. The incomplete inhibition of the response to KCl indicates other Ca2+ storage sites may also be mobilised by sarcolemmal depolarisation. Although the mechanism whereby CPA induces a large, sustained rise in [Ca2+]i remains unknown, the data lend support to the suggestion that depletion of intracellular Ca2+ storage sites may activate a Ca2+ entry pathway across the sarcolemma.

Cholinergic neuromuscular transmission in the longitudinal muscle of the guinea-pig ileum.

1. Brief transmural stimuli, 0.5-1 ms, initiated contractions of the longitudinal muscle taken from the guinea-pig ileum that were recorded isometrically. In separate preparations similar stimuli were found to initiate excitatory junction potentials which were recorded using intracellular recording electrodes. All of these responses were abolished by either tetrodotoxin, omega-conotoxin or hyoscine. 2. The contractions produced by increasing [K+]o were blocked by nifedipine, 1 x 10(-7) M; nicardipine, 1 x 10(-7) M; verapamil, 1 x 10(-5) M or diltiazem, 1 x 10(-5) M. In these solutions brief stimuli continued to initiate contractions: this indicates that neuronally released acetylcholine continues to trigger a contraction when muscle voltage-dependent calcium channels appear to have been blocked. 3. When membrane potential recordings were made from the smooth muscle layer, brief transmural stimuli initiated excitatory junction potentials that triggered muscle action potentials. Although muscle action potentials were abolished by low concentrations of a range of organic calcium antagonists, excitatory junction potentials persisted and continued to initiate contractions of reduced amplitude. 4. When the internal concentration of calcium ions, [Ca2+]i, was measured using fura-2, brief transmural stimuli caused an increase in [Ca2+]i. Part of this response, which occurred at a time corresponding to the unblocked excitatory junction potential, persisted in the presence of the organic calcium antagonist nifedipine. 5. Two explanations appear possible. Neuronally released acetylcholine may simultaneously activate non-selective cation channels and cause the release of Ca2+ from an internal store. Alternatively, neuronally released acetylcholine may cause an increase in [Ca2+]i which is separate from that which accompanies the activation of voltage-dependent calcium channels. At this stage there is little other anatomical or electrophysiological evidence to support this view.

Intracellular Ca2+, force and activation heat in rabbit papillary muscle: effects of 2,3-butanedione monoxime.

We have investigated the effects of 2,3-butanedione monoxime (BDM) and mannitol on Ca2+ metabolism in rabbit cardiac muscle. Simultaneous measurements of force and intracellular Ca2+ were made in right ventricular papillary muscles loaded with the fluorescent Ca2+ indicator fura-2. At a BDM concentration of 2 mM, peak isometric force was only 52% of control values and this was reduced to 18% at a concentration of 5 mM. The peak of the Ca2+ transient decreased by 8% at 2 mM BDM and by 18% at the higher concentration. In the presence of 362 mM mannitol peak isometric force decreased by 78% and there was a tendency for the peak of the Ca2+ transient to increase. A combination of 362 mM mannitol with 5 mM BDM completely inhibited force production despite peak Ca2+ levels that were no different from control values. In myothermic experiments under similar conditions the latency release protocol of Gibbs et al. (1988) and the BDM protocol of Alpert et al. (1989) were used to derive independent estimates of tension-independent (activation) heat in the same muscle. For both protocols the heat-stress relationship was well fitted by first-order linear regression. The activation heat estimate was significantly higher when measured with the latency release technique (2.31 mJ/g) compared with the BDM protocol (1.24 mJ/g). Our results confirm that in rabbit cardiac muscle low concentrations of BDM (2 mM) cause a marked inhibition of force development with little apparent effect on peak Ca2+ levels. Therefore, the lower activation heat estimates under these conditions may not be due to a reduced intracellular Ca2+ concentration. It is possible that the higher activation heat values obtained with protocols not involving chemical interventions may include the energy usage contributed by cellular processes that presumably do not occur in the presence of BDM and mannitol.

Contractile and metabolic properties of longitudinal smooth muscle from rat urinary bladder and the effects of aging.

Longitudinal smooth muscle strips taken from the urinary bladders of Sprague-Dawley rats, aged approximately 6 months and 24 months, were examined under a variety of conditions. Force development in response to electrical field stimulation and to cumulative addition of Ca2+ in the continual presence of 64 mM. KCl was the same in both adult and aged preparations. In response to cumulative additions of carbachol, however, it was observed that there was a shift to the right of the dose-response curve and a decrease in maximal force in the aged muscle strips. The maximal velocity of shortening was significantly lower in muscles from aged animals than in those from young adult animals. The metabolic tension cost during isometric contraction was, however, the same in both groups suggesting that the decline in Vus is largely due to factors not influencing energetic cost. The aged muscles also exhibited a lower basal metabolic rate and a reduced contribution of aerobic glycolysis to total metabolic energy production during both quiescence and stimulation under normoxic conditions than did muscles from young adult animals. They were, however, able to increase their rate of lactate production to the same levels as young adult muscles when stimulated under anoxic conditions.

Contractile activation properties of ventricular myocardium from hypothyroid, euthyroid and juvenile rats.

Contractile activation properties of intact and chemically skinned ventricular myocardium preparations were studied in juvenile (3-4 weeks old), adult euthyroid and adult hypothyroid rats. The rats were made hyperthyroid by treatment with iodine-131 and propylthiouracil. The ventricular muscle of euthyroid rats contains a mixture of isozymes of myosin while the myocardium of juvenile and hypothyroid rats are relatively pure in regard to V1 and V3 types of myosin respectively. No significant differences were found in either the maximum Ca2+ activated or rigor force developed by "chemically skinned" preparations in either the juvenile or hypothyroid groups compared with euthyroid adults, suggesting that there is no difference between myocardia with different isozymes of myosin in the intrinsic capacity to generate force. In the hypothyroid (V3) preparations there was a significant shift in the force/pCa relation to the left compared with the euthyroid adult (mixture of V1 and V3 isozymes). The force/pCa relation for the juvenile lay in between that for the hypothyroid and euthyroid adults. The greater apparent Ca2+ sensitivity to activation in the hypothyroid group may relate to a slower cross-bridge cycling rate or altered Ca2+ kinetics in ventricular myocardium with exclusively V3 isozyme. In intact papillary muscles differences were found in the dependence of force on extracellular [Ca2+] such that a higher extracellular [Ca2+] was required for muscles from hypothyroid animals to attain maximum twitch force than those from juveniles. The force/frequency relations also differed, with the hypothyroid group being better able to sustain force as stimulation frequency increased than the juvenile group.(ABSTRACT TRUNCATED AT 250 WORDS)