Cocaine- and stress-primed reinstatement of drug-associated memories elicit differential behavioral and frontostriatal circuit activity patterns via recruitment of L-type Ca2+ channels.

Cocaine-associated memories are critical drivers of relapse in cocaine-dependent individuals that can be evoked by exposure to cocaine or stress. Whether these environmental stimuli recruit similar molecular and circuit-level mechanisms to promote relapse remains largely unknown. Here, using cocaine- and stress-primed reinstatement of cocaine conditioned place preference to model drug-associated memories, we find that cocaine drives reinstatement by increasing the duration that mice spend in the previously cocaine-paired context whereas stress increases the number of entries into this context. Importantly, both forms of reinstatement require Cav1.2 L-type Ca2+ channels (LTCCs) in cells of the prelimbic cortex that project to the nucleus accumbens core (PrL→NAcC). Utilizing fiber photometry to measure circuit activity in vivo in conjunction with the LTCC blocker, isradipine, we find that LTCCs drive differential recruitment of the PrL→ NAcC pathway during cocaine- and stress-primed reinstatement. While cocaine selectively activates PrL→NAcC cells prior to entry into the cocaine-paired chamber, a measure that is predictive of duration in that chamber, stress increases persistent activity of this projection, which correlates with entries into the cocaine-paired chamber. Using projection-specific chemogenetic manipulations, we show that PrL→NAcC activity is required for both cocaine- and stress-primed reinstatement, and that activation of this projection in Cav1.2-deficient mice restores reinstatement. These data indicate that LTCCs are a common mediator of cocaine- and stress-primed reinstatement. However, they engage different patterns of behavior and PrL→NAcC projection activity depending on the environmental stimuli. These findings establish a framework to further study how different environmental experiences can drive relapse, and supports further exploration of isradipine, an FDA-approved LTCC blocker, as a potential therapeutic for the prevention of relapse in cocaine-dependent individuals.

A translational continuum of model systems for evaluating treatment strategies in Alzheimer's disease: isradipine as a candidate drug.

A growing body of evidence supports the 'calcium hypothesis' of Alzheimer's disease (AD), which postulates that a variety of insults might disrupt the homeostatic regulation of neuronal calcium (Ca(2+)) in the brain, resulting in the progressive symptoms that typify the disease. However, despite ongoing efforts to develop new methods for testing therapeutic compounds that might be beneficial in AD, no single bioassay permits both rapid screening and in vivo validation of candidate drugs that target specific components of the Ca(2+) regulatory machinery. To address this issue, we have integrated four distinct model systems that provide complementary information about a trial compound: the human neuroblastoma MC65 line, which provides an in vitro model of amyloid toxicity; a transgenic Drosophila model, which develops age-dependent pathologies associated with AD; the 3×TgAD transgenic mouse, which recapitulates many of the neuropathological features that typify AD; and the embryonic nervous system of Manduca, which provides a novel in vivo assay for the acute effects of amyloid peptides on neuronal motility. To demonstrate the value of this 'translational suite' of bioassays, we focused on a set of clinically approved dihydropyridines (DHPs), a class of well-defined inhibitors of L-type calcium channels that have been suggested to be neuroprotective in AD. Among the DHPs tested in this study, we found that isradipine reduced the neurotoxic consequences of ß-amyloid accumulation in all four model systems without inducing deleterious side effects. Our results provide new evidence in support of the Ca(2+) hypothesis of AD, and indicate that isradipine represents a promising drug for translation into clinical trials. In addition, these studies also demonstrate that this continuum of bioassays (representing different levels of complexity) provides an effective means of evaluating other candidate compounds that target specific components of the Ca(2+) regulatory machinery and that therefore might be beneficial in the treatment of AD.

Isradipine antagonizes hypobaric hypoxia induced CA1 damage and memory impairment: Complementary roles of L-type calcium channel and NMDA receptors.

Hypobaric hypoxia leads to cognitive dysfunctions due to increase in intracellular calcium through ion channels. The purpose of this study was to examine the temporal contribution of L-type calcium channels and N-methyl-D-aspartate receptors (NMDARs) in mediating neuronal death in male Sprague Dawley rats exposed to hypobaric hypoxia simulating an altitude of 25,000 ft for different durations. Decreasing exogenous calcium loads by blocking voltage-gated calcium influx with isradipine (2.5 mg kg(-1)), and its efficacy in providing neuroprotection and preventing memory impairment following hypoxic exposure was also investigated. Effect of isradipine on calcium-dependent enzymes mediating oxidative stress and apoptotic cell death was also studied. Blocking of L-type calcium channels with isradipine reduced hypoxia-induced activation of calcium dependent xanthine oxidases, monoamine oxidases, cytosolic phospholipase A(2) and cycloxygenases (COX-2) along with concomitant decrease in free radical generation and cytochrome c release. Increased expression of calpain and caspase 3 was also observed following exposure to hypobaric hypoxia along with augmented neurodegeneration and memory impairment which was adequately prevented by isradipine administration. Administration of isradipine during hypoxic exposure protected the hippocampal neurons following 3 and 7 days of exposure to hypobaric hypoxia along with improvement in spatial memory.

Antagonizing L-type Ca2+ channel reduces development of abnormal involuntary movement in the rat model of L-3,4-dihydroxyphenylalanine-induced dyskinesia.

BACKGROUND: Chronic L-3,4-dihydroxyphenylalanine (L-DOPA) treatment of Parkinson's disease (PD) leads to debilitating involuntary movements, termed L-DOPA-induced dyskinesia. Striatofugal medium spiny neurons (MSN) lose their dendritic spines and cortico-striatal glutamatergic synapses in PD and in experimental models of DA depletion. This loss of connectivity is triggered by a dysregulation of intraspine Cav1.3 L-type Ca2+ channels. Here we address the possible implication of DA denervation-induced spine pruning in the development of L-DOPA-induced dyskinesia. METHODS: The L-type Ca2+ antagonist, isradipine was subcutaneously delivered to rats at the doses of .05, .1, or .2 mg/kg/day, for 4 weeks, starting the day after a unilateral nigrostriatal 6-hydroxydopamine (6-OHDA) lesion. Fourteen days later, L-DOPA treatment was initiated. RESULTS: Isradipine-treated animals displayed a dose-dependent reduction in L-DOPA-induced rotational behavior and abnormal involuntary movements. Dendritic spine counting at electron microscopy level showed that isradipine (.2 mg/kg/day) prevented the 6-OHDA-induced spine loss and normalized preproenkephalin-A messenger RNA expression. Involuntary movements were not reduced when isradipine treatment was started concomitantly with L-DOPA. CONCLUSIONS: These results indicate that isradipine, at a therapeutically relevant dose, might represent a treatment option for preventing L-DOPA-induced dyskinesia in PD.

Opposite effects of a single IIIS5 mutation on phenylalkylamine and dihydropyridine interaction with L-type Ca2+ channels.

Replacement of L-type Ca(2+) channel alpha(1) subunit residue Thr-1066 in segment IIIS5 by a tyrosine residue conserved in the corresponding positions of non-L-type Ca(2+) channels eliminates high dihydropyridine sensitivity through a steric mechanism. To determine the effects of this mutation on phenylalkylamine interaction, we exploited the availability of Ca(v)1.2DHP(-/-) mice containing the T1066Y mutation. In contrast to dihydropyridines, increased protein-dependent binding of the phenylalkylamine (-)-[(3)H]devapamil occurred to Ca(v)1.2DHP(-/-) mouse brain microsomes. This effect could be attributed to an at least 2-fold increase in affinity as determined by saturation analysis and binding inhibition experiments. The latter also revealed a higher affinity for (-)-verapamil but not for (-)-gallopamil. The mutation caused a pronounced slowing of (-)-[(3)H]devapamil dissociation, indicating a stabilization of the drug-channel complex. The increased affinity of mutant channels was also evident in functional studies after heterologous expression of wild type and T1066Y channels in Xenopus laevis oocytes. 100 mum (-)-verapamil inhibited a significantly larger fraction of Ba(2+) inward current through mutant than through WT channels. Our results provide evidence that phenylalkylamines also interact with the IIIS5 helix and that the geometry of the IIIS5 helix affects the access and/or binding of different chemical classes of Ca(2+) channel blockers to their overlapping binding domains. Mutation of Thr-1066 to a non-L-type tyrosine residue can be exploited to differentially affect phenylalkylamine and dihydropyridine binding to L-type Ca(2+) channels.

Effects of isradipine on cocaine-induced subjective mood.

We hypothesized that in humans, as in animals, isradipine, a dihydropyridine-class calcium channel antagonist, would antagonize cocaine's rewarding effects, based on preclinical evidence that isradipine inhibits cocaine-mediated increases in mesolimbic dopamine (DA), thereby reducing cocaine's abuse liability. Confirmation of our hypothesis would make isradipine a promising medication for treating cocaine dependence. Eighteen male and female volunteers (mean age, 32.6 years) who met Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria for cocaine dependence participated in a double-blind, placebo-controlled, crossover study. Subjects received placebo or sustained-release (SR) low-dose or high-dose isradipine (15 or 30 mg), plus placebo or low-dose or high-dose cocaine HCl (0.325 or 0.650 mg/kg), for 9 treatment sessions separated by a 2-day interval. Standardized assessments of abuse liability, including a choice procedure to determine preference for cocaine with and without isradipine over monetary incentives, were conducted at scheduled intervals. Cocaine administration produced dose-related prototypic increases in stimulant-related effects, including euphoria, and drug preference over monetary incentives. Isradipine lacked any stimulant or abuse liability effects or the propensity to elicit craving, and it did not antagonize any of cocaine's stimulant-related effects associated with its abuse liability. In conclusion, SR isradipine (up to 30 mg) does not antagonize cocaine's rewarding effects in cocaine-dependent individuals. While higher isradipine doses may have been more effective at antagonizing cocaine reward, we could not test such doses due to the risk of serious adverse events. Also, isradipine-mediated inhibition of mesolimbic DA release may be an ineffective treatment of cocaine dependence.

Cronobiología y cronoterapia en la hipertensión arterial: implicaciones diagnósticas, pronósticas y terapéuticas / Chronobiology and chronotherapy in hypertension: diagnostic, prognostic and therapeutic implications

La presión arterial se caracteriza por una marcada variación circadiana. La cronoterapia de la hipertensión arterial toma en cuenta los aspectos clínicos relevantes de la variación de la presión arterial a lo largo del día; en concreto, la elevación matutina y el descenso durante el período de descanso nocturno, así como las posibles modificaciones en las características farmacocinéticas y farmacodinámicas de los fármacos antihipertensivos en función del instante circadiano de su administración. Las diferencias dependientes de la hora de ingesta en la cinética (es decir, cronocinética) y los efectos tanto beneficiosos como adversos (cronodinámica) de los fármacos antihipertensivos son conocidos. Así, el patrón de variación circadiano de presión arterial claramente alterado en pacientes hipertensos con fallo renal crónico sólo se normaliza cuando se administra isradipino en la tarde, pero no en la mañana. Por su parte, la curva dosis-respuesta, la cobertura terapéutica y la eficacia de la doxazosina GITS dependen marcadamente del instante circadiano de administración del fármaco. Además, la administración de valsartán a la hora de acostarse, pero no a la hora de levantarse, mejora significativamente la relación de medias diurna/nocturna de la presión arterial. De esta forma la hora óptima de administración de valsartán podría elegirse en función del perfil circadiano basal dipper o no-dipper de cada paciente para una mejor eficacia terapéutica y reducción del riesgo cardiovascular. La hipertensión nocturna, caracterizada por la pérdida del descenso esperado en la presión arterial del 10 por ciento-20 por ciento durante las horas de descanso nocturno, aumenta el riesgo de eventos cerebrocardiovasculares. La cronoterapia proporciona soluciones para el tratamiento individualizado en función del perfil circadiano de presión arterial de cada paciente y podría así suponer un nuevo avance hacia una mejora en la optimización del control de presión arterial y en la reducción del riesgo cardiovascular (AU)

Isradipine prevents the development of spontaneously occurring cardiac necrosis in cardiomyopathic hamster.

Recent studies on the heart necrotizing process at the early stages of hamster polymyopathy have led us to believe that this hereditary disease derives from an anomalous transmembrane ion flux due to the presence of slow Na+ channels that contribute to intracellular Na+ accumulation which promote intracellular Ca2+ overload via the Ca2+ influx through the Na+-Ca2+ exchanger. In the present study, we investigated the potential beneficial effect of chronic treatment with a dual L-type Ca2+ and slow Na+ channel blockers isradipine, on the development of necrosis in myopathic hamster hearts. Young cardiomyopathic (CM) hamsters (CMH) were treated with isradipine (0.1 mg x kg(-1) x day(-1)) and nifedipine (1 mg x kg(-1) x day(-1)) for 4 consecutive weeks. Microscopic assessments were carried out in staged serial paraffin sections of heart ventricles from tissues freshly dissected at autopsy. In comparison with control nontreated hearts, which exhibited numerous necrotic calcific foci, myolytic lesions, and dilated right ventricle, isradipine treatment prevented, in a significant manner, all the above spontaneous pathological changes, while nifedipine had no effect. Our present observations provide evidence for the first time that in vivo treatment with a DHP Ca2+ channel blocker, isradipine, is cardioprotective against the development of necrosis in hereditary cardiomyopathy in the hamster. It is possible that the protective effect of isradipine in CMH could be largely due to the indirect blockade of Ca2+ influx through the Na+-Ca2+ exchanger as well as to possible direct blockade of Ca2+ influx through the T-type Ca2+ channel.

Role of L-type Ca2+ channels in attenuated morphine antinociception in streptozotocin-diabetic rats.

The role of L-type Ca2+ channels in morphine antinociception was studied in streptozotocin-induced diabetic and control rats, using [3H]PN200-110 [isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-methoxycabonylpyridine-3-caboxylate] binding (0.005-1.0 nmol/l) and rat whole brain membranes, to determine if the attenuation of morphine antinociception was related to alterations in dihydropyridine-sensitive Ca2+ channel binding characteristics. The tail-flick antinociceptive effect of morphine (4 mg/kg, i.p.) was significantly reduced in diabetic rats in comparison to that in controls. Nimodipine (0.1-3 mg/kg, i.p.) did not produce antinociception but significantly potentiated the morphine response in control rats. Nimodipine (0.3-3 mg/kg, i.p.) reversed the attenuation of morphine antinociception in a dose-dependent manner in diabetic rats. Moreover, insulin (2 U/kg, s.c.) [correction of mu/kg] reversed the attenuated morphine antinociception in streptozotocin-diabetic rats. A significant increase in the Bmax (+41%) of [3H]PN200-110 binding was observed in diabetic rat brain membranes compared to that in control rats. However, there was no change in affinity (Kd) value of [3H]PN200-110. The reduced morphine response in diabetic rats, in accordance with up-regulation of dihydropyridine sites, may be due to an increased Ca2+ influx through L-type channels. These results suggest a functional role of L-type Ca2+ channels in morphine antinociception and the diabetic state may lead to alterations in their density.

In vitro response of mitochondrial succinate oxidase system to epinephrine in human blood lymphocytes from health individuals and patients with neurocirculatory dystonia.

Activities of succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (hyaloplasmic and mitochondrial: alpha-GPDHH and alpha-GPDHM) in peripheral blood lymphocytes, and the response of SDH activity to exogenous epinephrine in vitro (the epinephrine test) were studied in 20 healthy subjects and 46 patients with hypertensive neurocirculatory dystonia. Activities of SDH, alpha-GPDHH, and alpha-GPDHM in blood lymphocytes and SDH adrenoreactivity in epinephrine test were higher in patients than in healthy controls. Treatment with hypotensive agents (isradipin and pyrroxan) moderated adrenoreactivity. Phytotherapy normalized the baseline activities of succinate oxidase system and alpha-glycerophosphate pathway in blood lymphocytes.

alpha 1D (Cav1.3) subunits can form l-type Ca2+ channels activating at negative voltages.

In cochlea inner hair cells (IHCs), L-type Ca(2+) channels (LTCCs) formed by alpha1D subunits (D-LTCCs) possess biophysical and pharmacological properties distinct from those of alpha1C containing C-LTCCs. We investigated to which extent these differences are determined by alpha1D itself by analyzing the biophysical and pharmacological properties of cloned human alpha1D splice variants in tsA-201 cells. Variant alpha1D(8A,) containing exon 8A sequence in repeat I, yielded alpha1D protein and L-type currents, whereas no intact protein and currents were observed after expression with exon 8B. In whole cell patch-clamp recordings (charge carrier 15-20 mm Ba(2+)), alpha1D(8A) - mediated currents activated at more negative voltages (activation threshold, -45.7 versus -31.5 mV, p < 0.05) and more rapidly (tau(act) for maximal inward currents 0.8 versus 2.3 ms; p < 0.05) than currents mediated by rabbit alpha1C. Inactivation during depolarizing pulses was slower than for alpha1C (current inactivation after 5-s depolarizations by 90 versus 99%, p < 0.05) but faster than for LTCCs in IHCs. The sensitivity for the dihydropyridine (DHP) L-type channel blocker isradipine was 8.5-fold lower than for alpha1C. Radioligand binding experiments revealed that this was not due to a lower affinity for the DHP binding pocket, suggesting that differences in the voltage-dependence of DHP block account for decreased sensitivity of D-LTCCs. Our experiments show that alpha1D(8A) subunits can form slowly inactivating LTCCs activating at more negative voltages than alpha1C. These properties should allow D-LTCCs to control physiological processes, such as diastolic depolarization in sinoatrial node cells, neurotransmitter release in IHCs and neuronal excitability.

Properties of voltage-gated Ca(2+) channels in rabbit ventricular myocytes expressing Ca(2+) channel alpha(1E) cDNA.

Using the whole-cell patch-clamp technique, we have studied the properties of alpha(1E) Ca(2+) channel transfected in cardiac myocytes. We have also investigated the effect of foreign gene expression on the intrinsic L-type current (I(Ca,L)). Expression of green fluorescent protein significantly decreased the I(Ca,L). By contrast, expression of alpha(1E) with beta(2b) and alpha(2)/delta significantly increased the total Ca(2+) current, and in these cells a Ca(2+) antagonist, PN-200-110 (PN), only partially blocked the current. The remaining PN-resistant current was abolished by the application of a low concentration of Ni(2+) and was little affected by changing the charge carrier from Ca(2+) to Ba(2+) or by beta-adrenergic stimulation. On the basis of its voltage range for activation, this channel was classified as a high-voltage activated channel. Thus the expression of alpha(1E) did not generate T-like current in cardiac myocytes. On the other hand, expression of alpha(1E) decreased I(Ca,L) and slowed the I(Ca,L) inactivation. This inactivation slowing was attenuated by the beta(2b) coexpression, suggesting that the alpha(1E) may slow the inactivation of I(Ca,L) by scrambling with alpha(1C) for intrinsic auxiliary beta.

Amlodipine, a calcium channel inhibitor, and cocaine and ethanol's reinforcing effects.

The effects of amlodipine (from 0.1 to 3.0 mg/kg) on rats' pressing for rewarding brain stimulation, with and without cocaine administration, were assessed. None of the doses reliably modified the effects of cocaine. Also, amlodipine was given to two groups of rats taking alcohol: one group that was regularly taking a sweetened alcoholic beverage and the other taking an unsweetened alcoholic beverage. The only discernible effects of amlodipine on alcohol intake were associated with the highest dose and only with rats taking the sweetened beverage. The effects of this high dose could easily be attributable to behavioral toxicity elicited by the dose. In contrast, and confirming previous work, isradipine, another calcium channel inhibitor, produced reliable reductions on both cocaine's and alcohol's reinforcing effects. Despite the similarity of isradipine and amlodipine, isradipine apparently has some unique features with respect to cocaine and alcohol.

Isradipine, a dihydropyridine-class calcium channel antagonist, attenuates some of d-methamphetamine's positive subjective effects: a preliminary study.

RATIONALE: Dopamine (DA) pathways in the midbrain mediate d-methamphetamine's rewarding effects associated with its abuse liability. Isradipine, a dihydropyridine-class calcium channel antagonist, reduces the rewarding effects of psychostimulants such as cocaine and d-amphetamine, presumably by antagonizing these central DA pathways. This is the first experiment to test the hypothesis that the rewarding effects of d-methamphetamine, like other psychostimulants, can be reduced by isradipine. OBJECTIVE: We studied the effects of high dose isradipine (0.21 mg/kg orally), on the positive subjective effects associated with the abuse liability of low and high dose d-methamphetamine (0.21 mg/kg and 0.42 mg/kg orally, respectively). METHODS: Using a double-blind, double-dummy, placebo-controlled, Latin-Square, cross-over design, 18 healthy male and female volunteers received each of the following six treatments separated by a rest period of 2-7 days: a) placebo+placebo; b) low-dose d-methamphetamine+placebo); c) high-dose d-methamphetamine+placebo; d) high dose isradipine+placebo); e) low-dose d-methamphetamine+high dose isradipine, and f) high-dose d-methamphetamine+high dose isradipine. RESULTS: d-Methamphetamine produced orderly increases in positive subjective measures of both stimulation and mood. Pre-treatment with isradipine significantly reduced some of these positive subjective effects and craving for d-methamphetamine. CONCLUSION: Isradipine as an anti-reward or craving reducing medication is a promising therapeutic agent for the treatment of d-methamphetamine dependence.

Rational use of calcium-channel antagonists in Raynaud's phenomenon.

Raynaud's phenomenon (RP) is a peripheral circulatory disorder characterized by sudden episodes of digital artery spasm, often precipitated by cold temperature or emotional stress. Although the cause of RP is not fully known, it appears to involve inappropriate adrenergic response to cold stimuli. Treatment of RP is conservative in most patients, but in patients with severe disease includes the use of agents that promote digital vasodilation. The calcium-channel antagonists, particularly the dihydropyridine derivative nifedipine, are the most thoroughly studied drug class for the treatment of RP. Approximately two thirds of patients respond favorably, with significant reductions in the frequency and severity of vasospastic attacks. Nifedipine use is often limited by the appearance of adverse vasodilatory effects such as headache or peripheral edema. The newer second-generation dihydropyridines such as amlodipine, isradipine, nicardipine, and felodipine also appear to be effective in patients with RP and may be associated with fewer adverse effects.

Effects of isradipine, an L-type calcium channel blocker on permanent and transient focal cerebral ischemia in spontaneously hypertensive rats.

Permanent or transient focal cerebral ischemia was induced in spontaneously hypertensive rats (SHR) using the intraluminal filament method. Successful occlusion of the middle cerebral artery (MCA) was achieved using 4/O filaments (terminal diameter 0.20-0.25 mm) coated with poly-L-lysine. The L-type calcium channel blocker isradipine (2.5 mg/kg) administered subcutaneously 30 min following permanent MCA occlusion significantly reduced the volume of ischemic brain damage in the cerebral hemisphere (25%; P = 0.0001), cerebral cortex (18%; P = 0.0034), and caudate nucleus (33%; P = 0.0002) when assessed at 24 h post-MCA occlusion. Isradipine did not affect the functional deficit (measured using a subjective neurological scoring system) induced by MCA occlusion. In SHR undergoing transient (2 h) MCA occlusion isradipine administered 30 min post-MCA occlusion produced a significant reduction (47%; P = 0.001) in hemispheric infarct volume, whereas isradipine administered at the onset of reperfusion did not confer any significant neuroprotection. No change in functional deficit was seen with isradipine with either dosing paradigm at 24 h post-MCA occlusion. These results demonstrate that the intraluminal filament method of MCA occlusion can be used in the SHR strain and also substantiates the neuroprotective efficacy of isradipine in SHR models of permanent and transient focal cerebral ischemia.

Interactions between darodipine or isradipine and the 5-HT1A receptor agonist 8-OHDPAT in rat brain.

Isradipine and darodipine are dihydropyridine calcium antagonists that affect the serotonergic pathways with a peculiar profile of effects because, at low dose (0.08 and 0.3 mg/kg, respectively) they facilitate, but at high dose (1.60 and 5.0 mg/kg, respectively) they inhibit the serotonergic neurotransmission. To investigate the mechanisms of these effects, the selective 5-HT1A receptor agonist 8-OHDPAT was injected S.C. to rats pretreated I.P. with isradipine (0.04-1.60 mg/kg) or darodipine (0.3-5.0 mg/kg). By stimulating presynaptic 5-HT1A autoreceptor, 8-OHDPAT induced signs of inhibition of the serotonergic neutransmission (i.e., decrease of the 5-HIIA/5-HT ratio), but it also produced behavioral effects by stimulating postsynaptic 5-HT1A receptors (i.e., forepaw treadings). A low dose of isradipine (0.08 mg/kg) or darodipine (0.3 mg/kg) antagonized the presynaptic, but enhanced the postsynaptic effects of 8-OHDPAT, suggesting relief of the autoreceptor-mediated inhibition of the 5-HT release. Thus, the amine released could stimulate postsynaptic receptors, adding its action to that of 8-OHDPAT. A high dose of isradipine (1.60 mg/kg) or darodipine (5.0 mg/kg) left unchanged, or also enhanced, the signs of inhibition of serotonergic neurotransmission displayed by 8-OHDPAT, reducing but not suppressing the increase in the behavioral response to the stimulation of postsynaptic 5-HT1A receptors. It was speculated that the effects of isradipine and darodipine on scrotonergic pathways of rat brain could be due to changes in the back-regulation of the neurotransmission, mediated by 5-HT1A autoreceptors. This mechanism of action could be extended to other dihydropyridine calcium antagonists, because blockade of L-type VSCC by these compounds appears to be involved in their effects on brain 5-HT turnover.

Alleviation of the peripheral hemodynamic effects of dexmedetomidine by the calcium channel blocker isradipine.

BACKGROUND: Alpha 2-adrenergic agonists have peripheral vasoconstrictive effects and central sympatholytic and sedative effects. Whereas the latter are the basis of their use in anesthesia, the former could limit their clinical application. METHODS: To study whether a vasodilator could alleviate the systemic and coronary vasoconstrictor effects of dexmedetomidine without influencing the central sympatholytic effects, the calcium channel blocker isradipine was infused after a high dose of dexmedetomidine in anesthetized dogs. RESULTS: Dexmedetomidine 10 micrograms.kg-1 decreased plasma concentrations of norepinephrine and epinephrine by more than 90%, heart rate by 39%, cardiac output by 64%, dp/dtmax by 29% and increased mean arterial pressure by 55% and the left ventricular end-diastolic pressure (LVEDP) 4-fold as compared to baseline. In addition, coronary blood flow decreased by 52% and coronary venous oxygen saturation by 51%. Isradipine could completely antagonize all the coronary and systemic hemodynamic changes induced by dexmedetomidine, but only partially he increase in LVEDP. Isradipine caused no changes in plasma catecholamine levels. CONCLUSION: Isradipine could alleviate the peripheral hemodynamic actions of dexmedetomidine while having no effect on its central sympatholytic properties.

Regulation of the L-type calcium channel alpha-1 subunit by chronic depolarization in the neuron-like PC12 and aortic smooth muscle A7r5 cell lines.

The regulation of L-type voltage-dependent Ca2+ channels by chronic depolarization was studied in the aortic smooth muscle A7r5 and neuron-type PC12 cell lines, by probing the expression and the functional state of their constitutive alpha-1 subunits. PC12 cells showed, after prolonged exposure to a high-K+ depolarizing solution, a 25% reduction of the functional Ca2+ channel density which was accompanied by a decrease of the alpha-1 subunit mRNA expression. In A7r5 cells submitted to a similar protocol of depolarization, 45Ca2+ uptake measurements revealed a fall in the functional activity of L-type Ca2+ channels which was not related to a modulation of their mRNA expression, but arose from a long-term voltage-dependent channel inactivation. Accordingly, the lag time and the mechanisms of recovery were different in the two cell types. In PC12 cells, when restoring physiological culture conditions, de novo synthesis of alpha-1 subunits allowed the recovery of the original density of L-type Ca2+ channels at the membrane surface. As for the A7r5 cells, we showed that after chronic depolarization, the complete restoration of the resting membrane potential and the related Ca2+ channel activity required a 2-day incubation in physiological medium and could probably be related to a normalization of the increased intracellular Ca2+ concentration. In contrast, it is noteworthy that, in PC12 cells, the only transient increase of intracellular Ca2+ content in the first hours of depolarization could account for the long-term down-regulation of L-type Ca2+ channels.

Effects of isradipine and nifedipine retard in hypertensive patients with type II diabetes mellitus.

Twenty patients were randomized to receive either 2.5 mg isradipine twice daily or 20 mg nifedipine retard once daily for 6 months. After 2 weeks of placebo wash-out, evaluations were carried out every 4 weeks. These evaluations included assessment of blood pressure, lipid profile, hemoglobin A1 sigma glucagon, C peptide, and insulin requirements. Both isradipine and nifedipine retard lowered systolic and diastolic blood pressures to normal values (P < .001). However, isradipine was accompanied by a decrease in heart rate (P < .005). Neither drug modified hemoglobin A1c or the glycemic profile. The endogenous insulin-secretion response decreased in both treatment groups (P < .05). In conclusion, isradipine and nifedipine retard are efficacious in the treatment of hypertension in patients with type II diabetes mellitus, and neither treatment produces modification of metabolic control.