Calcium channels and calcium channel antagonists

A randomized sham-controlled trial on the effects of dual-tDCS "during" physical therapy on lower limb performance in sub-acute stroke and a comparison to the previous study using a "before" stimulation protocol

Background

Dual-transcranial direct current stimulation (tDCS) has been used to rebalance the cortical excitability of both hemispheres following unilateral-stroke. Our previous study showed a positive effect from a single-session of dual-tDCS applied before physical therapy (PT) on lower limb performance. However, it is still undetermined if other timings of brain stimulation (i.e., during motor practice) induce better effects. The objective of this study was to examine the effect of a single-session of dual-tDCS “during” PT on lower limb performance in sub-acute stroke and then compare the results with our previous data using a “before” stimulation paradigm.

Method

For the current “during” protocol, 19 participants were participated in a randomized sham-controlled crossover trial. Dual-tDCS over the M1 of both cortices (2 mA) was applied during the first 20 min of PT. The Timed Up and Go and Five-Times-Sit-To-Stand tests were assessed at pre- and post-intervention and 1-week follow-up. Then, data from the current study were compared with those of the previous “before” study performed in a different group of 19 subjects. Both studies were compared by the difference of mean changes from the baseline.

Results

Dual-tDCS “during” PT and the sham group did not significantly improve lower limb performance. By comparing with the previous data, performance in the “before” group was significantly greater than in the “during” and sham groups at post-intervention, while at follow-up the “before” group had better improvement than sham, but not greater than the “during” group.

Conclusion

A single-session of dual-tDCS during PT induced no additional advantage on lower limb performance. The “before” group seemed to induce better acute effects; however, the benefits of the after-effects on motor learning for both stimulation protocols were probably not different.

Trial registration Current randomized controlled trials was prospectively registered at the clinicaltrials.gov, registration number: NCT04051671. The date of registration was 09/08/2019.

Calcium Antagonists in the Management of Patients with Aneurysmal Subarachnoid Hemorrhage: A Review

Cerebral arterial vasospasm and infarction is the leading cause of death and disability among patients who reach a major medical center after aneurysmal subarachnoid hemorrhage (SAH). Recent evidence suggests that two calcium antagonists, nimodipine or nicardipine, may be useful in preventing this important complication of SAH. This paper reviews the current status of these two calcium antagonists in the management of SAH.

PROTECTION OF BLOOD-BRAIN BARRIER BREAKDOWN BY NIFEDIPINE IN ADRENALINE-INDUCED ACUTE HYPERTENSION

The question of whether influxes of ionic Ca+2 into cerebral endothelium plays an important role in increased vascular permeability consequent to an acute hypertension is not accurately resolved. We tested the effect of nifedipine, a calcium entry blocker, on the cerebrovascular permeability for proteins in adrenalin-induced acute hypertension. The experiments were carried out on male Wistar rats. The experimental groups consisted of normotensive saline controls, adrenaline-induced hypertensive rats, and adrenalin-induced hypertensive rats as pre-treated or post-treated with a bolus of nifedipine. Brains of hypertensive rats showed increased permeability to Evans Blue-Albumin complex, when blood pressure elevated rapidly to more than 170 mmHg. The number and size of areas of Evans-Blue extravasation were smaller if an increase in blood pressure was prevented. The short lasting elevation of blood pressure did not result in protein extravasation in brains of hypertensive rats. The results suggest that nifedipine can modify the permeability disruptions observed in acutely hypertensive rats. The data also support the hypothesis that Ca+2 may be responsible for the changes in permeability of BBB in hypertension by mediating the contraction of vascular muscles.

Differential cell-specific location of Cav-1 and Ca(2+)-ATPase in terminal Schwann cells and mechanoreceptive Ruffini endings in the periodontal ligament of the rat incisor

Caveolae are involved in clathrin-independent endocytosis, transcytosis, signal transduction, and tumor suppression - all of which depend on their main constituent protein caveolin families. The periodontal Ruffini ending has been reported to develop a caveola-like structure on the cell membrane of both the axon terminals and Schwann sheaths, suggesting the existence of an axon-Schwann cell interaction in the periodontal Ruffini endings. However, little information is available concerning the functional significance of these caveolae. The present study was undertaken to examine the immunolocalization of caveolin-1, -3 (Cav-1, Cav-3) and Ca(2+)-ATPase in the periodontal Ruffini endings of the rat incisor. Decalcified sections of the upper jaws were processed for immunocytochemistry at the levels of light and electron microscopy. Some immunostained sections were treated with histochemistry for nonspecific cholinesterase (nChE) activity. Observations showed the periodontal Ruffini endings were immunopositive for Cav-1, but not Cav-3. Immunoreactive products for Cav-1 were confined to caveola-like structures in the cell membranes of the cytoplasmic extensions and cell bodies of the terminal Schwann cells associated with the periodontal Ruffini endings. However, the axonal membranes of the terminals did not express any Cav-1 immunoreaction. Double staining with Ca(2+)-ATPase and either protein gene product 9.5 (PGP 9.5) or S-100 protein disclosed the co-localization of immunoreactions in the axonal branches of the periodontal Ruffini endings, but not in the terminal Schwann cells. As Ca(2+) plays an important role in mechanotransduction, these characteristic immunolocalizations show Cav-1/Ca(2+)-ATPase might be involved in the quick elimination of intracellular Ca(2+) in mechanotransduction.

Nifedipine regulated periodontal ligament remodeling: an experimental study in rats

OBJECTIVE

The aim of this study was to investigate the effects of nifedipine on periodontal ligament remodeling during orthodontic tooth movement.

MATERIAL AND METHODS

Sixty male Sprague-Dawley rats were randomly divided into an orthodontic group and groups that received either 10 mg/kg or 40 mg/kg nifedipine (NIF). Immunohistochemical staining and image analysis were used to investigate the expression of matrix metalloproteinase (MMP)-1, -10, -13 and collagen-I in PDL, and maxillary 1st molar displacement was measured.

RESULTS

Expression of MMP-1, -10, and -13 was significantly decreased in both NIF groups, while collagen-I expression was markedly increased. NIF significantly inhibited tooth movement.

CONCLUSIONS

NIF affects the expression of MMP-1, -10, -13 and collagen-I and tooth movement induced by orthodontic force in rats, thus indicating that calcium channels might be important in mediating PDL remodeling.

Spinal cord regeneration induced by a voltage-gated calcium channel agonist

Regeneration in the central nervous system (CNS) is prohibitive. This is likely due to an interplay of cellular (gene expression, growth factors) and environmental (inhibition by CNS myelin) factors. Calcium supports various intracellular functions, and multiple in vitro studies have shown a role of calcium in axonal growth. In this study, we examine the role of a calcium agonist, S(-)-Bay K 8644, in promoting or impeding CNS growth in vivo, in an effort to understand further the relationship between the voltage-gated L type calcium channel and regeneration. Using a well-established rat spinal cord model of regeneration, we have injected various doses of S(-)-Bay K 8644 (30-240 M) around the injured spinal cord. Our results demonstrate that S(-)-Bay K 8644 enhances regeneration in a dose-dependent fashion. In addition, at very specific concentrations, the same agonist has no effect on or even inhibits regeneration. We conclude that spinal regeneration is highly dependent on intracellular calcium concentration. Furthermore, depending on the dose used, the effect of calcium agonist supplementation on spinal regeneration can be supportive or inhibitory.

The Effect of Calcium Channel Antagonists on Spontaneous and Evoked Epileptiform Activity in the Rat Neocortex In Vitro

Calcium influx through voltage-activated calcium channels may play a crucial role in the propagation and maintenance of seizure activity. We have examined the contribution of various types of calcium currents to epileptogenesis by studying the effects of various calcium channel blockers on epileptiform activity. N-methyl-d-aspartate receptor-mediated epileptiform activity was induced by removal of magnesium ions superfusing the cortex, or by low-frequency stimulation of the underlying white matter. CoCl2, CdCl2 and omega-conotoxin, acting at the N- and L-type calcium channels, significantly reduced epileptiform activity. L-channel antagonists nifedipine and verapamil, and the agonist BAY K 8644, increased spontaneous bursting in cortical wedges, but had no effect upon evoked activity. The T-channel blocker NiCl2 had variable effects on epileptiform activity, whereas phenytoin consistently reduced such activity. These results suggest that calcium influx underlying epileptiform activity in the rat neocortex may occur at least partially via the activation of the N-type calcium channel. However, contributions from other calcium channel types cannot be excluded.

Differential inhibition of T-type calcium channels by neuroleptics

T-type calcium channels play critical roles in cellular excitability and have been implicated in the pathogenesis of a variety of neurological disorders including epilepsy. Although there have been reports that certain neuroleptics that primarily target D2 dopamine receptors and are used to treat psychoses may also interact with T-type Ca channels, there has been no systematic examination of this phenomenon. In the present paper we provide a detailed analysis of the effects of several widely used neuroleptic agents on a family of exogenously expressed neuronal T-type Ca channels (alpha1G, alpha1H, and alpha1I subtypes). Among the neuroleptics tested, the diphenylbutylpiperidines pimozide and penfluridol were the most potent T-type channel blockers with Kd values (approximately 30-50 nm and approximately 70-100 nm, respectively), in the range of their antagonism of the D2 dopamine receptor. In contrast, the butyrophenone haloperidol was approximately 12- to 20-fold less potent at blocking the various T-type Ca channels. The diphenyldiperazine flunarizine was also less potent compared with the diphenylbutylpiperadines and preferentially blocked alpha1G and alpha1I T-type channels compared with alpha1H. The various neuroleptics did not significantly affect T-type channel activation or kinetic properties, although they shifted steady-state inactivation profiles to more negative values, indicating that these agents preferentially bind to channel inactivated states. Overall, our findings indicate that T-type Ca channels are potently blocked by a subset of neuroleptic agents and suggest that the action of these drugs on T-type Ca channels may significantly contribute to their therapeutic efficacy.

Drug-induced alterations in tumour perfusion yield increases in tumour cell radiosensitivity

The perfusion of human tumour xenografts was manipulated by administration of diltiazem and pentoxifylline, and the extent that observed changes in tumour perfusion altered tumour radiosensitivity was determined. 2 tumour systems having intrinsically different types of hypoxia were studied. The responses of SiHa tumours, which have essentially no transient hypoxia, were compared to the responses of WiDr tumours, which contain chronically and transiently hypoxic cells. We found that relatively modest increases in net tumour perfusion increased tumour cell radiosensitivity in WiDr tumours to a greater extent than in SiHa tumours. Moreover, redistribution of blood flow within WiDr tumours was observed on a micro-regional level that was largely independent of changes in net tumour perfusion. Through fluorescence-activated cell sorting coupled with an in vivo-in vitro cloning assay, increases in the radiosensitivity of WiDr tumour cells at intermediate levels of oxygenation were observed, consistent with the expectation that a redistribution of tumour blood flow had increased oxygen delivery to transiently hypoxic tumour cells. Our data therefore suggest that drug-induced changes in tumour micro-perfusion can alter the radiosensitivity of transiently hypoxic tumour cells, and that increasing the radiosensitivity of tumour cells at intermediate levels of oxygenation is therapeutically relevant.

Diltiazem enhances tumor blood flow: MRI study in a murine tumor

PURPOSE

Diltiazem, a calcium-channel blocker, is known to differentially influence the radiation responses of normal and murine tumor tissues. To elucidate the underlying mechanisms, the effects of diltiazem on the radiation response of Ehrlich ascites tumor (EAT) in mice have been investigated, and the hemodynamic changes induced by diltiazem in tumor and normal muscle have been studied using magnetic resonance imaging (MRI) techniques.

METHODS AND MATERIALS

Ehrlich ascites tumors were grown subcutaneously in Swiss albino strain A mice. Dynamic gadodiamide and blood oxygen level dependent (BOLD) contrast enhanced 1H MR imaging studies of EAT and normal muscle were performed after administration of diltiazem in mice using a 4.7 Tesla MR scanner. Tumor radiotherapy experiments (total dose = 10 Gy, 0.4-0.5 Gy/min, single fraction) were carried out with 30 min preadministration of diltiazem (27.5 or 55 mg/kg i.p.) to EAT-bearing mice using a teletherapy machine.

RESULTS

The diltiazem+ radiation treated group showed significant tumor regression (in approximately/= 65% of the animals) and enhanced animal survival. MR-gadodiamide contrast kinetics revealed a higher magnitude of signal enhancement in diltiazem treated groups as compared to the controls. The observed changes in the magnitude of kinetic parameters were the same for both tumor and normal muscle. BOLD-MR images at 30 min after diltiazem administration showed a 25% and 8% (average) intensity enhancement from their basal values in tumor and normal muscle regions, respectively. The control group showed no significant changes.

CONCLUSION

The present studies demonstrate the radiosensitization potential of diltiazem in the mice EAT model. The enhanced radiation response observed with diltiazem correlates with the diltiazem-induced increase in tumor blood flow (TBF) and tumor oxygenation. The present results also demonstrate the applications of BOLD-MR measurements in investigating the alterations in tumor oxygenation status.

Postischemic changes of

Sequential alterations of [3H]nimodipine and [3H]ryanodine binding in gerbils were investigated in selectively vulnerable regions, such as the striatum and hippocampus, 1 h to 7 days after 10 min of transient cerebral ischemia. [3H]Nimodipine binding showed no significant changes in the striatum and hippocampus up to 48 h after ischemia. Seven days after ischemia, however, a severe reduction in [3H]nimodipine binding was observed in the dorsolateral striatum, hippocampal CA1 (stratum oriens, stratum pyramidale and stratum radiatum) and hippocampal CA3 sector. On the other hand, [3H]ryanodine binding showed a significant increase in the hippocampus 1 h after ischemia. Five hours after ischemia, a significant reduction in [3H]ryanodine binding was observed only in the hippocampal CA1 sector. Thereafter, the striatum and hippocampus showed no significant alterations in [3H]ryanodine binding up to 48 h after ischemia. After 7 days, a marked reduction in [3H]ryanodine binding was observed in the striatum and hippocampus which were particularly vulnerable to ischemia. These results demonstrate that postischemic alteration in [3H]nimodipine and [3H]ryanodine binding is produced with different processes in the hippocampus. They also suggest that the mechanism for striatal cell damage caused by transient cerebral ischemia may, at least in part, differ from that for hippocampal neuronal damage. Furthermore, our findings suggest that abnormal calcium release from intracellular stores may play a pivotal role in the development of hippocampal neuronal damage. Copyright Rapid Science Ltd

Chemical hypoxia triggers apoptosis of cultured neonatal rat cardiac myocytes: modulation by calcium-regulated proteases and protein kinases

Myocardial infarctions and stroke arise primarily as a result of hypoxia/ischemia-induced cell injury. However, the molecular mechanism of cardiac cell death due to hypoxia has not been elucidated. We showed here that chemical hypoxia induced by 1 mM azide triggered apoptosis of isolated neonatal rat ventricular cardiac myocytes but had no effect on cardiac fibroblasts. The azide-induced cardiomyocyte apoptosis could be characterized by a reversible initiation phase (0-46 h after azide exposure) during which cytosolic ATP levels remained little affected. This was followed by an irreversible execution phase (12-18 h) exhibiting prominent internucleosomal DNA fragmentation, cell membrane leakage, mitochondrial dysfunction, and increased calpain messenger RNA. Blocking extracellular calcium influx or intracellular calcium release was each effective in suppressing myocyte apoptosis. Cell death was also found to be mediated by calcium sensitive signal transduction events based on the use of specific antagonists. Consistent with the induction of calpain expression during apoptosis, blocking de novo protein synthesis and calpain activity inhibited cell death. These regulatory features coupled with the ease of the cell system suggest that the myocyte apoptosis model described here should be useful in the study of events leading to the demise of the myocardium.

Calcium channels in neurological disease

Channels involved in the influx and intracellular mobilization of calcium have been implicated as targets of diverse genetic and immune-mediated neurological diseases. These include the L-type voltage-gated calcium channel of skeletal muscle (hypokalemic periodic paralysis), the neuronal P/Q-type voltage-gated calcium channel (familial hemiplegic migraine, episodic ataxia type 2, spinocerebellar ataxia 6, and Lambert-Eaton myasthenic syndrome), and the skeletal muscle ryanodine receptor (malignant hyperthermia and central core disease). The discovery of these and other calcium channelopathies should help to clarify how different mutations affect channel function and how altered channel function produces disease, and may lead to new treatments for these conditions.

Relationship between specific binding of 125I-omega-conotoxin GVIA and GTP binding protein: effects of the GTP analogues, mastoparan and A1F4-

We investigated whether the specific binding or labeling of 125I-omega-CgTX on crude membranes from chick whole brain was affected when endogenous GTP binding protein (G protein) was activated by GTP analogues, mastoparan (MP) and aluminum fluoride (AIF4-; AICl3 + NaF). Both GTPgammaS and Gpp(NH)p attenuated the inhibitory effect of selective N-type Ca channel inhibitors such as aminoglycoside antibiotics (AGs) or dynorphine (1-13)(Dyn) on specific 125I-omega-CgTX binding in a dose-dependent manner. On the other hand, the inhibitory effects of the divalent metal cations Cd2+, Co2+, Mg2+ and Mn2- on such binding were not attenuated by GTPgammaS. MP and AIF4- also attenuated the inhibitory effect of Neo on this binding similar to GTPgammaS. The attenuating effect of MP was enhanced by the presence of Mg2+ in a dose-dependent manner. However, GTP analogues, MP and AIF4-, did not affect binding or labeling without AGs or Dyn. GTPgammaS, MP and AIF4- also attenuated the specific labeling of a 215-kDa band in crude membranes with 125I-omega-CgTX using the cross-linker DSS (non-reduced condition) in the presence of Neo. These results indicate that there are direct or indirect relationships between N-type Ca channels and G proteins via binding sites for AGs or MP.

Effects of vinconate on age-related alterations in [3H]MK-801, [3H]glycine, sodium-dependent D-[3H]aspartate, [3H]FK-506 and [3H]PN200-110 binding in rats

We investigated the effects of age and (+/-)-methyl-3-ethyl-2,3,3a,4-tetrahydro-1 H-in-dolo[3,2,1-de] [1,5] naphthyridine-6-carboxylate hydrochloride (vinconate), an indolonaphthyridine derivative, on calcium channels, neurotransmitter receptor systems and immunophilin in Fischer rat brain using quantitative receptor autoradiography. [3H]MK-801, [3H]glycine, sodium-dependent D-[3H]aspartate, [3H]FK-506 and [3H]PN200-110 were used to label N-methyl-D-aspartate (NMDA) receptors, glycine receptors, excitatory amino acid transport sites, FK-506 binding proteins (FKBP) and voltage-dependent L-type calcium channels, respectively. [3H]Glycine and sodium-dependent D-[3H]aspartate binding significantly decreased in the frontal cortex, parietal cortex, striatum, nucleus accumbens, hippocampus, thalamus, substantia nigra and cerebellum of 24 month old rats in comparison with 6 month old animals. In contrast, [3H]MK-801, [3H]FK-506 and [3H]PN200-110 binding showed no significant changes in the brain of 24 month old rats. Intraperitoneal chronic treatment with vinconate (10 and 30 mg/kg, once a day for 4 weeks) dose-dependently ameliorated the significant reduction in [3H]glycine and sodium-dependent D-[3H]aspartate binding in the brain of 24 month old rats. These results demonstrate that glycine receptors and excitatory amino acid transport sites are more susceptible to aging processes than NMDA receptors, immunophilin and voltage-dependent L-type calcium channels. Furthermore, our findings suggest that vinconate may have a beneficial effect on age-related changes in glycine receptors and excitatory amino acid transport sites.

Neurochemical mechanisms in brain injury and treatment: a review

This article reviews cellular energy transformation processes and neurochemical events that take place at the time of brain injury and shortly thereafter emphasizing hypoxia-ischemia, cerebrovascular accident, and traumatic brain injury. New interpretations of established concepts, such as diffuse axonal injury, are discussed; specific events, such as free radical production, excess production of excitatory amino acids, and disruption of calcium homeostasis, are reviewed. Neurochemically-based interventions are also presented: calcium channel blockers, excitatory amino acid antagonists, free radical scavengers, and hypothermia treatment. Concluding remarks focus on the role of clinical neuropsychologists in validation of treatment interventions.

Binding and labeling of omega-conotoxin GVIA in crude membranes from subfractionated fractions and various areas of chick brain

Specific binding and specific labeling of 125I-omega-CgTX were investigated in crude membranes from both subfractionated fractions and various brain areas in chick whole brain. The specific activities of the marker enzymes 2',3'-cyclic nucleotide 3'-phosphorylase, Na/K ATPase and succinic dehydrogenase in the subfractionated fractions were three- to five-fold higher than those in the P2 fraction. However, the amount of specific [125I] omega-CgTX binding in the fractions of synaptosomes and synaptic plasma membranes was only about 1.2-times higher than that in the P2 fraction. The characteristics of specific 125I-omega-CgTX labeling with disuccinimidyl suberate to the 135-kDa band were generally comparable to those of specific [125I] omega-CgTX binding sites. These results suggest that the specific binding sites of [125I] omega-CgTX were not localized the synaptosomes and synaptic plasma membranes fractions, although each fraction was well isolated from the others from which were decided by the strength of specific activity for marker enzymes.

Role of programmed (apoptotic) cell death during the progression and therapy for prostate cancer

Cells possess within their epigenetic repertoire the ability to undergo an active process of cellular suicide termed programmed (or apoptotic) cell death. This programmed cell death process involves an epigenetic reprogramming of the cell that results in an energy-dependent cascade of biochemical and morphologic changes (also termed apoptosis) within the cell, resulting in its death and elimination. Although the final steps (i.e., DNA and cellular fragmentation) are common to cells undergoing programmed cell death, the activation of this death process is initiated either by sufficient injury to the cell induced by various exogenous damaging agents (e.g., radiation, chemicals, viruses) or by changes in the levels of a series of endogenous signals (e.g., hormones and growth/survival factors). Within the prostate, androgens are capable of both stimulating proliferation as well as inhibiting the rate of the glandular epithelial cell death. Androgen withdrawal triggers the programmed cell death pathway in both normal prostate glandular epithelia and androgen-dependent prostate cancer cells. Androgen-independent prostate cancer cells do not initiate the programmed cell death pathway upon androgen ablation; however, they do retain the cellular machinery necessary to activate the programmed cell death cascade when sufficiently damaged by exogenous agents. In the normal prostate epithelium, cell proliferation is balanced by a equal rate of programmed cell death, such that neither involution nor overgrowth normal occurs. In prostatic cancer, however, this balance is lost, such that there is greater proliferation than death producing continuous net growth. Thus, an imbalance in programmed cell death must occur during prostatic cancer progression. The goal of effective therapy for prostatic cancer, therefore, is to correct this imbalance. Unfortunately, this has not been achieved and metastatic prostatic cancer is still a lethal disease for which no curative therapy is currently available. In order to develop such effective therapy, an understanding of the programmed death pathway, and what controls it, is critical. Thus, a review of the present state of knowledge concerning programmed cell death of normal and malignant prostatic cells will be presented.

Effect of calcium antagonist, nicardipine, on cerebral blood flow in postasphyxial newborn piglets

An experiment was carried out in nine piglets within 24 h after birth (control group: four, nicardipine group: five) for the purpose of evaluating the effects of a calcium antagonist, nicardipine, on cerebral blood flow changes induced by asphyxia neonatorum. Under respiratory control with a mechanical ventilator, the animals were exposed to hypoxia. The inspiratory oxygen level was lowered at 15 min intervals from 0.08 to 0.06 and then to 0.05. When bradycardia (heart rate; 60/min or less) was observed, 100% oxygen, adrenaline, and sodium bicarbonate were administered for resuscitation. Nicardipine was administered at a dosage of 10 micrograms/kg via bolus injection 30 min after the resuscitation. It was administered thereafter at a rate of 10 micrograms/kg per h. The cerebral blood flow was measured using a laser Doppler velocimeter. The cerebral blood flow, electroencephalograph (EEG), blood pressure, and heart rate were continuously measured for 120 min after the resuscitation. In the control group, the mean arterial pressure 35 min after the resuscitation was 60 mmHg or more. However, the cerebral blood flow was lower than the prehypoxia value in the animals with a mean arterial pressure of 75 mmHg or less. In the nicardipine group, the mean arterial pressure was lower, but the cerebral blood flow was higher than the prehypoxia value and cerebral ischemia was not induced. The mean arterial pressure 120 min after the resuscitation was 72.0 +/- 8.2 mmHg in the control group, while it was 56.7 +/- 7.5 mmHg in the nicardipine group. It was significantly lower in the latter.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of [125I]omega-conotoxin labeling using bifunctional cross linker DSP in crude membranes from chick brain

Characteristic of [125I]omega-conotoxin (omega-CgTX) labeling using bifunctional cross linker (dithio bis[succinimidyl propionate]:DSP) was systematically investigated in crude membranes from chick whole brain. [125I]omega-CgTX specifically labeled 216 kDa as a main and 236 kDa as a minor bands in the crude membranes under non-reduced condition, but not labeled under reduced condition. We investigated the effect of various Ca channel antagonists on [125I]omega-CgTX labeling with DSP in detail, and found that there is a strong correlation between the effects of Ca channel antagonists on [125I]omega-CgTX labeling of the 216 kDa band and specific [125I]omega-CgTX binding. These results suggest that labeling of the 216 kDa band under non-reduced condition with [125I]omega-CgTX using DSP involves the specific binding sites of [125I]omega-CgTX, perhaps including one of the neuronal N-type Ca channel subunits in the crude membranes.

Characteristics of specific 125I-omega-conotoxin GVIA binding and 125I-omega-conotoxin GVIA labeling using bifunctional crosslinkers in crude membranes from chick whole brain

Characteristics of specific 125I-omega-conotoxin GVIA (125I-omega-CgTX) binding and 125I-omega-CgTX labeling using bifunctional crosslinkers were systematically investigated in crude membranes from chick whole brain. Aminoglycosides and dynorphine A (1-13) inhibited the specific binding of 125I-omega-CgTX, but not that of the L-type calcium ion channel antagonist [3H](+)PN200-110. It seems likely that the inhibitory effect of dynorphine A (1-13) does not involve kappa-opiate receptors, based on results with the opiate receptor antagonist naloxone and the kappa-opiate receptor agonist U50488H. Spider venom, Cd2+ and La3+ inhibited the specific binding of 125I-omega-CgTX, as well as that of [3H](+)PN200-110. Various L-type Ca2+ channel antagonists did not affect the specific binding of 125I-omega-CgTX. 125I-omega-CgTX specifically labeled 135 kDa and 215 kDa bands in crude membranes under reduced and non-reduced conditions, respectively. The crosslinker disuccinimidyl suberate (DSS) yielded better 125I-omega-CgTX labeling than the other two crosslinkers tested. We investigated the effect of various Ca2+ channel antagonists on 125I-omega-CgTX labeling with DSS in detail, and found that there is a strong correlation between the effects of Ca2+ channel antagonists on 125I-omega-CgTX labeling of the 135 kDa band and specific 125I-omega-CgTX binding. These results suggest that aminoglycosides and dynorphine A (1-13) are specific inhibitors of specific 125I-omega-CgTX binding, and that labeling of the 135 kDa band with 125I-omega-CgTX using DSS involves the specific binding sites of 125I-omega-CgTX, perhaps including one of the neuronal N-type Ca2+ channel subunits in the crude membranes.

(S)-emopamil reduces brain edema from collagenase-induced hemorrhage in rats

BACKGROUND AND PURPOSE

Calcium channel blockers reduce edema due to cerebral ischemia, but little is known about their usefulness in hemorrhage. Therefore, we studied the effect of the calcium channel blocker (S)-emopamil in collagenase-induced hemorrhage.

METHODS

Adult rats had hemorrhagic necrosis induced by the intracerebral injection of 0.4 U of bacterial collagenase. Six groups of rats were given either 10 or 20 mg/kg (S)-emopamil at different times after induction of the lesion. Brain water and electrolyte levels in these rats were measured 24 hours after collagenase injection. Also, lesion volume in other rats was measured either 4 or 24 hours after formation of the lesion with the drug given at 1 hour or both 1 and 5 hours, respectively.

RESULTS

Administration of 20 mg/kg (S)-emopamil 1 hour after lesion induction significantly decreased water and electrolyte content in both posterior regions (P < .05). This beneficial effect was lost when a second 20-mg/kg dose was given at 5 hours. A single 20-mg/kg injection at 1 hour had no effect on lesion volume at 4 hours. Two doses significantly increased volume at 24 hours (P < .05).

CONCLUSIONS

Early administration of (S)-emopamil is beneficial in hemorrhagic lesions, but a subsequent delayed injection may be deleterious. Knowledge of the time of hemorrhage will be important in use of these agents in treating hemorrhage.

Postischemic administration of AK275, a calpain inhibitor, provides substantial protection against focal ischemic brain damage

Experiments were conducted to determine whether a potent, reversible calpain inhibitor could reduce the cortical ischemic brain damage associated with focal ischemia in the rat. AK275 (Z-Leu-Abu-CONH-CH2CH3), the active isomer of the diastereomeric mixture, CX275, was employed in conjunction with a novel method of perfusing drug directly onto the infarcted cortical surface. This protocol reduced or eliminated numerous, nonspecific pharmacokinetic, hemodynamic, and other potentially confounding variables that might complicate interpretation of any drug effect. Focal ischemia was induced using a variation of the middle cerebral artery occlusion method. These studies demonstrated a reliable and robust neuroprotective effect of AK275 over the concentration range of 10 to 200 microM (perfused supracortically at 4 microliters/h for 21 h). Moreover, a 75% reduction in infarct volume was observed when initiation of drug treatment was delayed for 3 h postocclusion. Our data further support an important role of calpain in ischemia-induced neuropathology and suggest that calpain inhibitors may provide a unique and potentially powerful means of treating stroke and other ischemic brain incidents.

Synthesis and in vivo evaluation of [11C]semotiadil, a benzothiazine calcium antagonist

A carbon-11 labeled benzothiazine calcium antagonist, (+)-(R)-2-[5-methoxy-2-[3-[methyl[2-[(3,4- methylenedioxy)phenoxy]ethyl]amino]propoxy]phenyl]-4-methyl-2H-1,4- benzothiazin-3(4H)-one (semotiadil), and its enantiomer were prepared by N-methylation of the corresponding norderivatives with 11CH3I: decay-corrected radiochemical yields of 16-27% based on 11CH3I, radiochemical, chemical and optical purity of > 99%, sp. act. of 11-50 GBq/mumol and preparation time of 35-40 min. In mice, saturable and stereo-selective uptake in the hippocampus, striatum and hypothalamus was observed. The potential of the compound to visualize the regional brain calcium channels in vivo by positron emission tomography was indicated; however, no promising sign was found in the myocardium.

Characteristics of specific 125I-omega-conotoxin GVIA binding in rat whole brain

Characteristics of specific 125I-omega-conotoxin (omega-CgTX) binding were systematically investigated in crude membranes from rat whole brain. Kd and Bmax Values for the binding were 49.7 pM and 181.5 fmol/mg of protein, respectively. The effects of various types of Ca channel antagonists on the binding were investigated. Dynorphin A (1-13), in particular, specifically inhibited 125I-omega-CgTX binding, but not that of [3H](+)PN200-110. Spider venom from Plectreurys tristes did not specifically inhibit specific binding of 125I-omega-CgTX, because the venom also inhibited the binding of [3H](+)PN200-110 to a similar degree. The amount of specific binding of 125I-omega-CgTX was less in the cerebellum than that in any other area of whole brain. The cross-linker disuccinimidyl suberate did not label with 125I-omega-CgTX and its binding sites in rat whole brain, although it did in chick whole brain, which was used as a positive control. These findings suggested that dynorphine A (1-13) was a selective blocker of omega-CgTX-sensitive Ca channels in crude membranes from rat whole brain and that omega-CgTX-sensitive Ca channels were mainly present a rat brain except cerebellum.

Enhancement of the epidural morphine-induced analgesia by systemic nifedipine

We evaluated postoperative pain relief and incidence of side effects of the combination of epidural morphine (0.5 mg) and sublingual nifedipine (10 mg). Thirty-six patients were submitted to elective operations and divided into 4 groups receiving placebo (groups A and B) or morphine (groups C and D) by the epidural route, followed by sublingual placebo (groups A and C) or nifedipine (groups B and D) administered in a double-blind fashion. The mean (+/- S.E.M.) periods of analgesia were 16.6 +/- 1.6 (A), 15 (B) 105 +/- 77.0 (C), and 428.8 +/- 72.0 (D) min. No patient had pruritus, excessive sedation or respiratory depression. Episodes of nausea and/or vomiting requiring no specific therapy were observed in groups A, B and D. Nifedipine-treated groups also had a significant fall in blood pressure which was controlled by rehydration. These results indicate that epidural morphine-induced postoperative pain relief may be enhanced by systemic administration of nifedipine, with easily controlled side effects.

Specific bindings of [3H](+)PN200-110 and [125I]omega-conotoxin to crude membranes from differentiated NG108-15 cells

The characteristics of the specific bindings of [3H](+)PN200-110 (PN: L-type Ca channel antagonist) and [125I]omega-conotoxin G VI A (omega-CgTX: neuronal L- or N-type Ca channel antagonist) to crude membranes from undifferentiated neuroblastoma X glioma hybrid NG108-15 (NG108-15) cells and differentiated cells induced with dibutyryl cAMP (Bt2cAMP) were examined, because we have already observed that the magnitude and rate of KCl-stimulated 45Ca uptake by NG108-15 cells increased progressively during differentiation of the cells induced with Bt2-cAMP (unpublished results). The specific binding of [3H](+)PN to these crude membranes was saturable at various concentrations of 2.5-5.0 nM [3H](+)PN. Scatchard analysis showed that the specific binding of [3H](+)PN at equilibrium was significantly increased after differentiation of the NG108-15 cells with Bt2cAMP, but that the apparent Kd value for the specific binding of [3H](+)PN was not influenced by treatment with Bt2cAMP. The specific binding of [3H](+)PN to crude membranes from Bt2cAMP-treated NG108-15 cells was inhibited by a calcium agonist and antagonists, the order of their inhibitory potencies being (+)PN > nitrendipine > (-)PN > or = Bay K 8644 > > diltiazem = verapamil. Thus, PNs showed significant stereoselective inhibition of the specific binding of [3H](+)PN. On the other hand, [125I]omega-CgTX at concentrations of 0.075-0.6 nM showed scarcely any specific binding to these crude membranes, although at 0.6 nM it showed specific binding to crude membranes from rat brain in the same experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of 45Ca uptake stimulated by high KCl of differentiated and undifferentiated NG108-15 and PC12h cells

The characteristics of KCl-stimulated 45Ca uptake by neuroblastoma X glioma hybrid NG108-15 cells induced to differentiate with dibutyryl cAMP (Bt2cAMP) and of PC12h pheochromocytoma cells induced to differentiate with nerve growth factor (NGF) were studied. The extent and rate of KCl-stimulated 45Ca uptake by differentiated NG108-15 cells induced with Bt2cAMP were significantly higher than those of the undifferentiated cells. However, differentiation of PC12h cells induced with NGF did not enhance their extent or rate of KCl-stimulated 45Ca uptake. The effects of Ca agonist and antagonists indicated that the characteristics of KCl-stimulated 45Ca uptake by Bt2cAMP-treated NG108-15 cells and NGF-treated PC12h cells mainly reflected those of peripheral L-type voltage-sensitive calcium channels activated by high KCl. These results suggest that differentiated neural cells did not all show an enhanced capacity for KCl-stimulated 45Ca uptake, although the characteristic patterns of differentiation (extension of neurite-like processes, etc.) and that of effect by Ca agonist or antagonists on NG108-15 cells and PC12h cells were similar.

Blockade of glutamate excitotoxicity and its clinical applications

Glutamate has long been known to play a vital role in the normal functioning of neurons, serving as the main excitatory neurotransmitter in the central nervous system. The normal function of glutamate, as a means of communication from one neuron to the next, breaks down in certain disease states. Under particular scrutiny has been the etiology of neuronal damage caused by ischemic disease, seen most commonly in cerebrovascular embolic disease, commonly known as a stroke. It has been shown that damage associated with ischemic disease in the brain is not a direct result of hypoxia or deprivation of metabolic intermediates. In fact, the crucial role is played by an excessive efflux of glutamate by ischemic neurons, which then in turn activates pathways in post-synaptic neurons leading to acute cell swelling and later, cell death. An extremely hopeful development in the field of glutamate excitotoxicity has been the application of therapeutic methods aimed at attenuating the damaging action of glutamate, in an effort to decrease morbidity associated with such common diseases as stroke and other neurodegenerative disorders.

Non-opioid antitussives potentiate some behavioural and EEG effects of N-methyl-D-aspartate channel blockers

The effects of the non-opioid oral antitussives dextromethorphan (DM) and caramiphen (CP) were tested against the behavioural and EEG effects elicited by the N-methyl-D-aspartate (NMDA) antagonists dizocilpine (MK 801) and phencyclidine (PCP) in rats and mice. PCP (1.25-10 mg/kg i.p.) induced a dose-dependent increase/decrease of the locomotor/exploratory activity of mice. DM (25-50 mg/kg i.p.) and MK 801 (0.125-0.250 mg/kg i.p.) induced an increase of the locomotor/exploratory activity of mice, while CP (25-50 mg/kg i.p.) did not produce such an effect. CP (12.5 mg/kg i.p.) and DM (12.5 mg/kg i.p.) significantly potentiated the effects of PCP (1.25 mg/kg i.p.) and MK 801 (0.062 mg/kg i.p.) in the open field test in mice. In rats, PCP (1.25-10 mg/kg i.p.) induced three dose-dependent EEG stages: 1) increase of the cortical desynchronization periods; 2) increase of the amplitude of cortical background activity; 3) appearance of cortical slow wave-spike complexes. Even though DM (up to 100 mg/kg i.p.) only induced PCP-like EEG stage 1 by itself, and CP (up to 50 mg/kg i.p.) did not affect basal cortical EEG activity, these drugs, at the doses of 30-50 mg/kg i.p., potentiated all the EEG effects induced by PCP. These data support the view of an interaction between non-opioid antitussives and non-competitive NMDA antagonists.

Evaluation of a novel calcium channel blocker, (S)-emopamil, on regional cerebral edema and neurobehavioral function after experimental brain injury

The authors investigated the effects of a novel calcium channel blocker, (S)-emopamil, on cerebral edema and neurobehavioral and memory function following experimental fluid-percussion brain injury in the rat. Two independent experiments were performed to evaluate the effects of this compound on cardiovascular variables and postinjury cerebral edema (increases in tissue water content), and on cognitive deficits and neurological motor function following brain injury. Treatment with (S)-emopamil significantly reduced focal brain edema at 48 hours after brain injury. Profound memory dysfunction induced by brain injury was significantly attenuated following (S)-emopamil treatment. In addition, (S)-emopamil also attenuated the deficits in motor function that were observed over a 2-week period following brain injury. These results suggest that changes in calcium homeostasis may play an important role in the pathogenesis of trauma to the central nervous system and that the calcium channel blocker (S)-emopamil might be a useful compound for the treatment of traumatic brain injury.

Ultrastructural localization of calcium in mechanoreceptors of the oral mucosa

Cytochemical localization of Ca2+ in Meissner corpuscles and Merkel cell-neurite complexes in the palatine mucosa of the Mongolian gerbil was studied by a combined oxalate antimonate-microwave irradiation procedure. The reaction products obtained were identified as calcium antimonate by EGTA solubility and X-ray microanalysis. Meissner corpuscles in the normal palatine rugae could be roughly classified into three types by amount and localization of Ca2+. Type I corpuscles were characterized by a high Ca2+ content in both the terminal axoplasm and caveolae of the lamellar plates, type II, by a low Ca2+ content in the terminal axoplasm and a high Ca2+ content in the lamellar cytoplasm. Type III corpuscles showed intermediate characteristics. Palatine rugae stimulated mechanically during fixation contained an increased number of type I corpuscles. On the other hand, two patterns were distinguished in the distribution of Ca2+ in Merkel cells in palatine rugae fixed under normal conditions. One showed abundant Ca2+ dispersed throughout the cell, while in the other, Ca2+ was specifically localized in the Golgi apparatus and mitochondria. Similar distribution patterns also were observed in palatine rugae that had received mechanical stimulus during fixation. Axon terminals of most Merkel cell-neurite complexes in normal palatine rugae were poor in axoplasmic Ca2+, whereas those in most Merkel cell-neurite complexes in mechanically stimulated palatine rugae contained abundant Ca2+ in their axoplasm.

Programmed cell death: its possible contribution to neurotoxicity mediated by calcium channel antagonists

Organic calcium channel antagonists attenuate ischemic or excitotoxic neuronal injury, probably by limiting Ca2+ influx through the voltage-gated calcium channels. However, the possibility that calcium channel antagonists may compromise neuronal survival with long-term exposure has not been systemically examined. In the present study, we report that cerebral cortical cultures exposed for 2 days to either nifedipine, verapamil, diltiazem, or flunarizine, undergo selective neuronal degradation in a concentration-dependent fashion. This degeneration could be attenuated by protein synthesis inhibitors cycloheximide and actinomycin-D. Cortical cultures incubated for 2 days in low calcium media also exhibit widespread neuronal damage, which is similarly blocked by cycloheximide. Although we cannot exclude other possibilities, these findings suggest that a decrease in intraneuronal calcium levels may trigger synthesis of proteins mediating neuronal cell death. Regardless of the exact toxic mechanisms involved, additional studies on neurotoxicity of calcium channel antagonists seem warranted since some of these compounds are currently being clinically used.

Pathophysiology and treatment of focal cerebral ischemia. Part I: Pathophysiology

This article examines the pathophysiology of lesions caused by focal cerebral ischemia. Ischemia due to middle cerebral artery occlusion encompasses a densely ischemic focus and a less densely ischemic penumbral zone. Cells in the focus are usually doomed unless reperfusion is quickly instituted. In contrast, although the penumbra contains cells "at risk," these may remain viable for at least 4 to 8 hours. Cells in the penumbra may be salvaged by reperfusion or by drugs that prevent an extension of the infarction into the penumbral zone. Factors responsible for such an extension probably include acidosis, edema, K+/Ca++ transients, and inhibition of protein synthesis. Central to any discussion of the pathophysiology of ischemic lesions is energy depletion. This is because failure to maintain cellular adenosine triphosphate (ATP) levels leads to degradation of macromolecules of key importance to membrane and cytoskeletal integrity, to loss of ion homeostasis, involving cellular accumulation of Ca++, Na+, and Cl-, with osmotically obligated water, and to production of metabolic acids with a resulting decrease in intra- and extracellular pH. In all probability, loss of cellular calcium homeostasis plays an important role in the pathogenesis of ischemic cell damage. The resulting rise in the free cytosolic intracellular calcium concentration (Ca++) depends on both the loss of calcium pump function (due to ATP depletion), and the rise in membrane permeability to calcium. In ischemia, calcium influx occurs via multiple pathways. Some of the most important routes depend on activation of receptors by glutamate and associated excitatory amino acids released from depolarized presynaptic endings. However, ischemia also interfers with the intracellular sequestration and binding of calcium, thereby contributing to the rise in intracellular Ca++. A second key event in the ischemic tissue is activation of anaerobic glucolysis. The main reason for this activation is inhibition of mitochondrial metabolism by lack of oxygen; however, other factors probably contribute. For example, there is a complex interplay between loss of cellular calcium homeostasis and acidosis. On the one hand, a rise in intracellular Ca++ is apt to cause mitochondrial accumulation of calcium. This must interfere with ATP production and enhance anaerobic glucolysis. On the other hand, acidosis must interfere with calcium binding, thereby contributing to the rise in intracellular Ca++.

Effects of GTP analogues and activation of endogenous protein kinases on photoaffinity labeling with [3H](+)PN200-110 of crude membranes from rat heart and brain

The effects of GTP analogues and conditions in which various endogenous protein kinases were activated on photoaffinity labeling with [3H](+)PN200-110 (PN) of crude membranes from rat cardiac muscle and whole brain were investigated. Photoaffinity labeling with 20 nM [3H](+)PN of these crude membranes was decreased by 100 microM GTP-gamma-S, but not by 100 microM GTP or 100 microM GDP-beta-S. Similar results were obtained on the effects of GTP and its analogues on the specific binding of 20 nM [3H](+)PN to these crude membranes under the same conditions. Activation of endogenous protein kinases in these crude membranes did not influence the photoaffinity labeling with [3H](+)PN. These results suggested the binding sites, or DPH-sensitive, or L-type, calcium channels in curde membranes from rat cardiac muscle and whole brain are directly or indirectly modulated by endogenous GTP-binding protein, but not by various endogenous protein kinases in these crude membranes.

Calbindin-D28K-containing neurons in animal models of neurodegeneration: possible protection from excitotoxicity

Brain levels of the calcium binding protein Calbindin-D28K (CaBP28K) and CaBP28K mRNA were measured for various animal models of neurodegenerative diseases (MPTP-treated C57BL/6J mice and Sprague-Dawley rats receiving striatal/intraperitoneal kainic acid or quinolinic acid into the nucleus basalis magnocellularis). Brain areas were tested (radioimmunoassay, Western blot, slot blot, and Northern blot) for levels of CaBP28K and CaBP28K mRNA. The various models did not exhibit any changes in protein or mRNA levels from the controls, suggesting that CaBP28K-containing neurons were not lost after exposure to these neurotoxins. Immunocytochemical characterization of the substantia nigra of the MPTP-treated mice revealed that there was significant dopaminergic cell loss in this brain area after MPTP treatment. The majority of dopaminergic neurons that degenerated did not contain CaBP28K. The small percentage of surviving neurons were CaBP28K-positive. These results suggest that the presence of CaBP28K may protect neurons from calcium-mediated neurotoxicity.

Verapamil and valproic acid treatment of prolonged mania

The case of an adolescent with severe mental retardation, blindness, and a complex of behavioral symptoms consistent with mania is reported. Symptoms include an increased activity level, mood liability, irritability, hyposomia, and severe self-injurious behavior. The successful use of verapamil and valproic acid in the treatment of prolonged mania in this child is described.

Nicardipine reduces the levels of leukotriene C4 and prostaglandin E2, following different ischemic periods in rat brain tissue

Ischemic depolarization of nerve membranes is associated with a rapid influx of calcium into the cell, resulting in production of arachidonic acid (AA) metabolites. These metabolites, particularly leukotriene C4 (LTC4) have a very potent vasoconstrictor effect on cerebral arteries inducing vasogenic edema that may damage the ischemic penumbra. Calcium antagonists are assumed to prevent or reduce metabolic disturbances associated with ischemia. In this study, after developing an experimental animal model simulating the concept of the ischemic penumbra in the rat, the levels of LTC4 and prostaglandin E2 (PGE2) produced in the forebrain following different ischemic periods, such as 4th, 15th, 60th and 240th min were measured by a bioassay method, including 6 rats for each ischemic group. Then the effect of the 1-4 dihydropyridine nicardipine (1 mg/kg) on these mediators was investigated by giving it to the rat 30 min before the development of the ischemic model in each corresponding group (n = 6). We showed that nicardipine significantly reduced the high levels of LTC4 and PGE2 in the 4th min and 4th h of cerebral ischemia (p less than 0.005, p less than 0.0005). So it may be concluded that institution of nicardipine may be helpful in protecting the ischemic penumbra during the early hours of cerebral ischemia.

Diltiazem alters some withdrawal signs in pentobarbital-dependent rats

Male, Sprague-Dawley rats were made dependent on pentobarbital sodium (PB) by continuous, IP infusion of PB for 13 days. On Day 14, a 72-hour PB-free period began during which body weight, 24-hour water consumption and withdrawal scores were noted. In Study 1, rats were placed into one of four treatment groups at the start of the PB-free period. Groups included saline-infused control rats with twice daily administration of either vehicle or diltiazem and PB-dependent rats treated twice daily with either diltiazem or vehicle. In Study 2, rats were placed into one of the four treatment groups at the start of the 13-day PB-infusion period. In Study 1, PB-dependent rats treated with diltiazem exhibited approximately 10% loss of body weight at both 12 and 48 hours of the PB-free period while PB-dependent rats treated with vehicle exhibited only about a 5% loss of body weight. PB-dependent rats treated with either diltiazem or vehicle both exhibited about a 40% decline in water consumption and were noted to have significant increases in withdrawal scores by the fifth hour of the PB-free period. As compared to the scores of PB-dependent rats treated with vehicle, diltiazem did not significantly alter the withdrawal scores of PB-dependent rats at any time point during the PB-free period. In Study 2, the chronic administration of diltiazem to PB-infused rats produced both a significant decrease in water consumption at 48 and 72 hours and a significant increase in withdrawal scores from 3-48 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

[3H]nitrendipine binding in temporal cortex in Alzheimer's and Huntington's diseases

Specific [3H]nitrendipine binding which was shown to be calcium- and calmodulin-dependent was found to be significantly reduced in the temporal cortex in Alzheimer's disease compared to age-matched controls. Scatchard analysis revealed that this reduction was due to a loss in the number of cortical [3H]nitrendipine binding sites rather than a change in the affinity of the binding site in the Alzheimer patients. The reduction in cortical [3H]nitrendipine-specific binding was most marked in those Alzheimer's disease cases where the duration of the dementing illness was longer than two years. In contrast, no reduction in cortical [3H]nitrendipine binding was found in Huntington's disease. There was no significant correlation found between age (38-89 years) and [3H]nitrendipine binding in control cases, or between mean overall plaque counts and [3H]nitrendipine binding in the Alzheimer's disease cases. There was a significant correlation found between age (46-88 years) and [3H]nitrendipine binding in the Alzheimer's disease cases where the duration of the dementing illness was greater than two years.

Parathyroid hormone selectively inhibits L-type calcium channels in single vascular smooth muscle cells of the rat

1. The active synthetic N-terminal fragment of bovine parathyroid hormone, bPTH-(1-34) at a concentration of 1 microM, decreased the peak amplitude of the long-lasting (L-type) calcium channel current by 37% (n = 14, P less than 0.01) in rat tail artery smooth muscle cells. By contrast, this fragment of parathyroid hormone (PTH) (1 microM) had no effect on the transient (T-type) calcium channel current in the same cell preparation. 2. The inhibitory effect of bPTH-(1-34) on L-channel currents was reversible and could be antagonized by the L-channel agonist, Bay K 8644. In contrast, bPTH-(1-34) inhibited Bay K 8644-induced amplification of L-channel currents. 3. The inhibitory effect of bPTH-(1-34) on L-Channel currents was dose dependent with a threshold concentration of less than 10(-7), and voltage dependent with increased inhibition at more positive holding potentials. However, this effect of bPTH-(1-34) was not dependent on different pulse lengths or interpulse intervals. 4. The kinetics of deactivation of L-channel currents were not changed although the instantaneous amplitude of the L-channel tail current was reduced by bPTH-(1-34). 5. Application of bPTH-(1-34) antagonists (10(-6) M-bPTH-(3-34) and 10(-5) M-bPTH-(7-34] did not result in any significant change in the magnitude of L-channel currents (n = 15 and n = 7, respectively). 6. Pre-incubation of cells with bPTH-(3-34) for more than 15 min abolished the inhibitory effect of bPTH-(1-34) on L-channel currents. 7. The present study provides direct evidence to demonstrate the PTH, an endogenous circulating hormone, is a selective inhibitor of L-channel currents in vascular smooth muscle cells.