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At least 19 recordsLinked to original sources
PubMed1992

Different effects of L-, N- and T-type calcium channel blockers on striatal dopamine release measured by microdialysis in freely moving rats.

Using a microdialysis method, we have investigated effects of the voltage-dependent calcium channel blockers, verapamil, nicardipine, omega-conotoxin and flunarizine on the dopamine release and metabolism in the striatum of freely moving rat. Perfusion of verapamil (1-300 microM) and nicardipine (1-100 microM), an L-type calcium channel blocker, into the striatum through the dialysis membrane showed a dose-dependent decrease of dopamine release in the dialysate and slight increase of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels. Treatment of omega-conotoxin (0.1, 1 microM), an N-type channel blocker, decreased about 50% basal dopamine release and slightly decreased DOPAC and HVA levels. Treatment with flunarizine (10 microM), an T-type channel blocker, did not affect the dopamine release and metabolism. From these data, it appears that treatments of the L- and N-type voltage-dependent calcium channel blockers in rat striatum suppress basal dopamine release, but T-type blocker does not suppress it, suggesting that L-, N- and T-type calcium channels regulate in vivo dopamine release in a different mechanism.

Animals↗
PubMed2024

The characterization of new de novo CACNA1G variants affecting the intracellular gate of Cav3.1 channel broadens the spectrum of neurodevelopmental phenotypes in SCA42ND.

PURPOSE: Missense de novo variants in CACNA1G, which encodes the Cav3.1 T-type calcium channel, have been associated with a severe, early-onset form of cerebellar disorder with neurodevelopmental deficits (SCA42ND). We explored a large series of pediatric cases carrying heterozygous variants in CACNA1G to further characterize genotype-phenotype correlations in SCA42ND. METHODS: We describe 19 patients with congenital CACNA1G-variants, including 6 new heterozygotes of the recurrent SCA42ND variants, p.(Ala961Thr) and p.(Met1531Val), and 8 unreported variants, including 7 missense variants, mainly de novo. We carried out genetic and structural analyses of all variants. Patch-clamp recordings were performed to measure their channel activity. RESULTS: We provide a consolidated clinical description for the patients carrying p.(Ala961Thr) and p.(Met1531Val). The new variants associated with the more severe phenotypes are found in the Cav3.1 channel intracellular gate. Calcium currents of these Cav3.1 variants showed slow inactivation and deactivation kinetics and an increase in window current, supporting a gain of channel activity. On the contrary, the p.(Met197Arg) variant (IS4-S5 loop) resulted in a loss of channel activity. CONCLUSION: This detailed description of several de novo missense pathogenic variants in CACNA1G, including 13 previously reported cases, supports a clinical spectrum of congenital CACNA1G syndrome beyond spinocerebellar ataxia.

Humans↗
PubMed1992

Selective role of N-type calcium channels in neuronal migration.

Analysis of neuronal migration in mouse cerebellar slice preparations by a laser scanning confocal microscope revealed that postmitotic granule cells initiate their migration only after the expression of N-type calcium channels on their plasmalemmal surface. Furthermore, selective blockade of these channels by addition of omega-conotoxin to the incubation medium curtailed cell movement. In contrast, inhibitors of L- and T-type calcium channels, as well as those of sodium and potassium channels, had no effect on the rate of granule cell migration. These results suggest that N-type calcium channels, which have been predominantly associated with neurotransmitter release in adult brain, also play a transient but specific developmental role in directed migration of immature neurons before the establishment of their synaptic circuits.

Animals↗
PubMed1992

L- and T-type Ca2+ channels in canine cardiac Purkinje cells. Single-channel demonstration of L-type Ca2+ window current.

Canine cardiac Purkinje cells contain both L- and T-type calcium currents, yet the single Ca2+ channels have not been characterized from these cells. Additionally, previous studies have shown an overlap between the steady-state inactivation and activations curves for L-type Ca2+ currents, suggesting the presence of L-type Ca2+ "window" current. We used the on-cell, patch-clamp technique to study Ca2+ channels from isolated cardiac Purkinje cells. Patches contained one or more Ca2+ channels 75% of the time. L-type channels were seen in 69% and T-type channels in 73% of these patches. With 110 mM Ba2+ as the charge carrier, the conductances of the L- and T-type Ca2+ channels were 24.2 +/- 0.8 pS (n = 9) and 9.0 +/- 0.5 pS (n = 8), respectively (mean +/- SEM). With 110 mM Ca2+ as the charge carrier, the conductance of the L-type Ca2+ channel decreased to 9.7 +/- 1.2 pS (n = 4), whereas the T-type Ca2+ channel conductance was unchanged. Voltage-dependent inactivation was shown for both L- and T-type Ca2+ channels, although for L-type Ca2+ channel with Ba2+ as the charge carrier, inactivation took at least 30 seconds at a potential of +40 mV. After channel inactivation was complete, L-type Ca2+ channel reopenings were observed following repolarizing steps into the window voltage range. Thus, our data identify both L- and T-type Ca2+ channels in cardiac Purkinje cells and demonstrate, at the single-channel level, L-type channel transitions expected for a window current. Window current may play an important role in shaping the action potential and in arrhythmogenesis.

Animals↗
PubMed1992

Blockade of potassium or calcium channels provokes modifications in TRH-induced TSH release from rat perifused pituitaries.

The aim of the present study was to determine the functional relationship between blockade of potassium or calcium channel activity and the initial burst of TSH secretion in response to TRH. Perifused rat pituitary fragments were stimulated by a 6-min pulse of physiological concentration of TRH (10 nM) in the presence or absence of pharmacological blockers of K+ or Ca2+ channels. Blockade of Ca(2+)-activated K+ channels with TEA (10 mM and 30 mM), apamin (200 nM), or charybdotoxin (50 nM) completely or partially blunted TRH-induced TSH release. By contrast, blockade of voltage-dependent K+ channels with 4-aminopyridine (4-AP) (500 microM) or with dendrotoxin (DTX) (350 nM) significantly increased TSH response. Moreover, blockade of T-type voltage-sensitive Ca2+ channels (VSCC) with NiCl (3 mM) or with diphenylhydantoin (100 microM) significantly (P < 0.01) reduced TSH response to TRH, whereas blockade of L-type Ca2+ channels with verapamil (50 microM) was ineffective. Our results suggest that secretion of TSH in response to nanomolar concentrations of TRH is correlated with stimulation of Ca(2+)-activated K+ channels, and inhibition of 4-AP-and DTX-sensitive voltage-dependent K+ channels; furthermore TSH response seems to depend on the activation of T-type VSCC.

Animals↗
PubMed1992

Voltage-dependent calcium entry in confluent bovine capillary endothelial cells.

Confluent bovine capillary endothelial cells display, when examined for voltage-dependent calcium entries using cell-attached channel recordings, two types of Ca2+ channels (4 and 23.5 pS in 110 mM Ba2+) both sensitive to the dihydropyridine Ca agonist BAY K 8644. In contrast to isolated cells, confluent cells display no T-type, low threshold activity, and Ca currents were typically only elicited at very depolarized potentials. In these cells, voltage-dependent calcium entries will only be made operative by substances able to shift their activation towards the resting potential.

Adrenal Medulla↗
PubMed1992

Characterization of voltage-dependent calcium currents in mouse motoneurons.

1. Calcium channel currents were measured with the whole-cell patch clamp technique in cultured, identified mouse motoneurons. Three components of current were operationally defined on the basis of voltage dependence, kinetics, and pharmacology. 2. Test potentials to -50 mV or greater (10 mM external Ca2+) elicited a low-voltage activated T-type current that was transient (decaying to baseline in less than 200 ms) and had a relatively slow time to peak (20-50 ms). A 1-s prepulse to -45 mV produced approximately half-maximal inactivation of this T current. 3. Two high-voltage activated (HVA) components of current (1 transient and 1 sustained) were activated by test potentials to -20 mV or greater (10 mM external Ca2+). A 1-s prepulse to -35 mV produced approximately half-maximal inactivation of the transient component without affecting the sustained component. 4. When Ba2+ was substituted for Ca2+ as the charge carrier, activation of the HVA components was shifted in the hyperpolarizing direction, and the relative amplitude of the transient HVA component was reduced. 5. Amiloride (1-2 mM) caused a reversible, partial block of the T current without affecting the HVA components. 6. The dihydropyridine agonist isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-nitro-3- pyridine-carboxylate [(+)-SDZ 202-791, 100 nM-1 microM)] shifted the activation of the sustained component of HVA current to more negative potentials and increased its maximal amplitude. Additionally, (+)-SDZ 202-791 caused the appearance of a slowed component of tail current.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗
PubMed1992

Block of T-type Ca channels in guinea pig atrial cells by antiarrhythmic agents and Ca channel antagonists.

Myocardial cells have two types of Ca channels commonly called T-type and L-type. Whole cell Ca channel currents in guinea pig atrial myocytes can be separated and quantitated by analyzing channel closing kinetics after a brief depolarization (tail current analysis). L-type Ca channels deactivate rapidly when the membrane is repolarized and T-type Ca channels deactivate relatively slowly. Ca channel block by the therapeutically useful Ca channel antagonists is voltage dependent, so it is desirable to study block of both channel types over an extended voltage range. Tail current analysis allows this and was used to study block of both types of Ca channels under identical conditions. Amiodarone, bepridil, and cinnarizine block T-type Ca channels more potently than L-type Ca channels when binding equilibrates at normal diastolic potentials (approximately -90 mV). None of these drugs is a selective blocker of T-type Ca channels because block of L-type Ca channels is enhanced when cells are almost completely depolarized. Although weak block of T-type Ca channels by 1,4-dihydropyridines has usually been reported, we found that felodipine blocks these channels with high affinity. When most T-type Ca channels are inactivated, the apparent dissociation constant (KI) is 13 nM. Felodipine also blocks T-type Ca channels in GH3 cells (a cell line derived from rat anterior pituitary), but KI = 700 nM. Thus, T-type Ca channels in different cell types are pharmacologically distinct. Felodipine can block L-type Ca channels in atrial cells more potently than T-type Ca channels, but block of L-type Ca channels is potent only at depolarized potentials; block of both channel types is comparable at normal diastolic membrane potentials. Felodipine and the 1,4-dihydropyridines isradipine and (-)-202-791 are approximately equipotent at blocking T-type Ca channels, but differ substantially in potency for block of L-type Ca channels. Block of T-type Ca channels may account for some of the pharmacological effects of 1,4-dihydropyridines and for the antiarrhythmic activity of amiodarone and bepridil.

Animals↗
PubMed1992

The angiotensin AT2 receptor modulates T-type calcium current in non-differentiated NG108-15 cells.

We report here that angiotensin II (AII) and the AT2 receptor-selective ligand, CGP 42112, modulate the T-type calcium current in non-differentiated NG108-15 cells, which express only AT2 receptors. Both peptides decrease the T-type calcium current at membrane potentials above -40 mV and shift the current-voltage curve at lower potentials with maximal effect between 5 and 10 min after application. These data describe a new cellular response to AII and suggest that the AT2 receptor mediates certain neurophysiological actions of this hormone.

Action Potentials↗
PubMed2026

Utero-placental calcium and magnesium ion channels: A systematic review of obstetric implications of their alterations.

Despite the established roles of calcium (Ca2+) and magnesium (Mg2+) in placental function and uterine contractility, limited information exists on how dysregulation of major ion channels contributes to poor pregnancy outcomes. We synthesized data on the consequences of Ca2+ and Mg2+ channelopathies in uterine and placental functions. Using PubMed, Wiley Online, AJOL, and Web of Science databases for article search, a systematic review of forty-nine papers published between 2000 and March 2026 was carried out and reported in accordance with the PRISMA 2020 guideline. Based on the PICO framework, eligible studies involving human, animal, and in vitro designs were chosen and subjected to narrative analysis. L-type and T-type voltage-gated Ca2+ channels, together with transient receptor potential channels, emerged as principal mediators of placental Ca2+ transport and myometrial contractility. Mechanosensitive Piezo1 channels mediate stretch-activated Ca2+ influx, while store-operated Ca2+ entry pathways involving STIM1-Orai1 sustain intracellular Ca2+ homeostasis. Potassium-Ca2+ coupling channels modulated membrane hyperpolarization and anti-labor effects, and intracellular regulators such as PMCA and RYR1 fine-tuned Ca2+ homeostasis. The Mg2+ transporters are essential for preserving Mg2+ homeostasis and regulating Ca2+-dependent excitability. Dysregulation of these ion channel systems was consistently linked to abnormal uterine contractility, preterm birth, preeclampsia, fetal growth restriction, and adverse pregnancy outcomes. Both Ca2+ and Mg2+ ion channelopathies represent both a potential therapeutic target and a mechanistic factor underlying key obstetric complications.

Female↗
PubMed1992

Calcium current variation between acutely isolated adult rat dorsal root ganglion neurons of different size.

1. The distribution of pharmacologically and/or biophysically unique Ca2+ current subtypes was studied in different diameter rat dorsal root ganglion (DRG) neuron cell bodies. DRG cells which fell into three diameter ranges, small (20-27 microns), medium (33-38 microns) and large (45-51 microns), were studied. T-type Ca2+ current was defined as low-threshold, rapidly inactivating current evoked by a weak test depolarization (-50 mV) from negative holding potentials (-80 to -100 mV), and which was sensitive to changes in holding potential. L-type Ca2+ current was defined as peak high-threshold Ca2+ current evoked from a holding potential of -60 mV and sensitive to blockade by 2 microM-nimodipine. N-type Ca2+ current was defined as peak high-threshold Ca2+ current evoked from a holding potential of -60 mV and sensitive to blockade by 0.9 microM-omega-conotoxin GVIA. 2. T-type Ca2+ currents were observed in small and medium diameter, but not in large diameter, DRG cell bodies. Large diameter DRG cell bodies had a small amount of low-threshold Ca2+ current but this current did not inactivate and was insensitive to a change in holding potential from -80 to -90 mV, and thus did not appear to be conducted through T-type Ca2+ channels. The T-type Ca2+ currents observed in medium diameter DRG cell bodies were considerably larger in amplitude (1-6 nA) than those observed in small diameter DRG cell bodies (100 pA-1 nA). This difference could not be accounted for by the difference in membrane surface area of small versus medium diameter DRG cell bodies. 3. The T-type Ca2+ currents observed in medium diameter DRG cells were sensitive to blockade by amiloride. Amiloride (500 microM) blocked 79.4 +/- 0.9% (mean +/- S.E.M.) of T-type Ca2+ current amplitude in six medium diameter DRG cell bodies which were held at -80 mV and depolarized to -50 or -40 mV. Amiloride (500 microM) failed to block high-threshold current in five medium diameter DRG cell bodies, indicating that it was specific for T-type Ca2+ current in these cells. 4. The percentage of peak whole-cell L-type Ca2+ current was significantly larger in small diameter DRG cell bodies (52.9 +/- 4.7% of total whole-cell Ca2+ current) than in medium diameter DRG cell bodies (6.6 +/- 3.9% of total whole-cell Ca2+ current) or large diameter DRG cell bodies (19.4 +/- 5.7% of total whole-cell Ca2+ current).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1992

Inositol tetrakisphosphate isomers and elevation of cytosolic Ca2+ in vasopressin-stimulated insulin-secreting RINm5F cells.

Signal generation during the stimulation of insulin secretion by arginine vasopressin (AVP) was investigated in RINm5F cells. AVP (0.1 microM) caused a biphasic cytosolic Ca2+ ([Ca2+]i) rise, namely a rapid transient marked elevation after stimulation followed by a series of oscillations. In the absence of extracellular Ca2+, the sustained oscillations were abolished, while the initial [Ca2+]i transient was only partly decreased, indicating that the former are due to Ca2+ influx and the latter due mainly to mobilization from internal Ca2+ stores. AVP also evoked a transient depolarization of the average membrane potential. AVP-induced Ca2+ influx during the sustained phase, which was strictly dependent on receptor occupancy, was attenuated by membrane hyperpolarization with diazoxide. However, blockade of Ca2+ channels of the L- or T-type was ineffective. AVP stimulated production of diacylglycerol and inositol phosphates; for the latter both [3H] inositol labeling and mass determinations were performed. A transient increase in Ins(1,4,5)P3 was followed by a marked enhancement of Ins(1,3,4,5)P4 (8-fold) peaking at 15 s and gradually returning to basal values. Ins(1,3,4,6)P4 and Ins(3,4,5,6)P4 exhibited the most long-lasting augmentation (4- and 1.7-fold, respectively), and therefore correlated best with the period of sustained [Ca2+]i oscillations. InsP5 and InsP6 were not elevated. The effects of AVP, including the stimulation of insulin secretion from perifused cells, were obliterated by a V1 receptor antagonist. In conclusion, AVP induces protracted [Ca2+]i elevation in RINm5F cells which is associated with long-lasting increases in InsP4 isomers. The accumulation of InsP4 isomers reflects receptor occupancy and accelerated metabolism of the inositol phosphates. Activation of second messenger-operated Ca2+ channels is not necessarily implicated because of the attenuating effect of membrane hyperpolarization.

Arginine Vasopressin↗
PubMed1992

Phenytoin partially antagonized L-type Ca2+ current in glucagon-secreting tumor cells (ITC-1).

Transmembrane Ca2+ currents were investigated by means of a whole-cell clamp technique in a hamster glucagon-secreting tumor cell line (ITC-1). Two types of Ca2+ current were identified in ITC-1 cells. The low-threshold and transient (T-type) current became detectable above the potential level around -60 mV and decayed rapidly with an inactivation time constant of 95 ms (at -40 mV and 23 degrees C), while the high-threshold and long-lasting (L-type) one was activated by depolarization more positive to -30 mV with non-inactivating kinetics. The voltage dependence and kinetics of these currents were identical to those reported in guinea-pig pancreatic alpha 2 cells. Both currents were augmented by equimolar substitution of Ca2+ with Ba2+ and completely abolished by adding 1 microM La3+. Phenytoin, a well known anti-epileptic drug and a postulated T-type specific Ca2+ current antagonist, surprisingly blocked the L-type current without affecting the T-type current in ITC-1 cells. While phenytoin antagonized the L-type Ba2+ current selectively, 60% of the current remained even in supramaximal concentration range over 500 microM. The residual component of the L-type current was completely abolished by adding nifedipine.

Animals↗
PubMed1992

Dopamine inhibits voltage-activated calcium channel currents in rat pars intermedia pituitary cells.

Several lines of evidence suggest that dopamine acts as a neurotransmitter that inhibits both hormone secretion and electrical activity in pituitary intermediate cells (melanotrophs). In this study we examined the effects of exogenously applied dopamine on voltage activated calcium currents recorded with the whole-cell mode of the patch-clamp technique from short-term primary cultures of melanotrophs. Two types of calcium currents were distinguished by their voltage dependence and kinetics of inactivation similar to the low voltage-activated currents (LVA; or T-type) and high voltage-activated currents (HVA; N&L-types) of calcium currents. Exogenously applied dopamine (2-20 microM) reversibly reduced both LVA and HVA types of calcium currents. Evidence for these results came from experiments in which LVA and HVA calcium currents were separated by stepping to different membrane potentials from a fixed holding potential (Vh) or by changing Vh. These results suggest that dopamine can regulate the entry of calcium into melanotrophs by acting on at least two different populations of calcium channels thereby affecting hormone secretion and electrical activity.

Animals↗
PubMed1992

P-type calcium channels in rat central and peripheral neurons.

The peptide toxin omega-Aga-IVA blocked P-type Ca2+ channel current in rat Purkinje neurons (KD approximately 2 nM) but had no effect on identified T-type, L-type, or N-type currents in a variety of central and peripheral neurons. omega-Aga-IVA blocked a substantial fraction of high threshold Ca2+ channel current in neurons from the hippocampal CA1 region (mean 26%), visual cortex (32%), spinal cord (45%), and dorsal root ganglia (23%), but less in hippocampal CA3 neurons (14%) and none in sympathetic neurons. In all cases, omega-Aga-IVA block could be reversed by a brief train of strong depolarizations. There was no overlap between current blocked by omega-Aga-IVA and the fractions blocked by dihydropyridines and omega-conotoxin GVIA, but not all current resistant to dihydropyridines and omega-conotoxin was blocked by omega-Aga-IVA. The results suggest that omega-Aga-IVA is highly selective for P-type channels and that many central neurons and some peripheral neurons possess substantial P-type current.

Animals↗
PubMed1992

Cholesterol increases the L-type voltage-sensitive calcium channel current in arterial smooth muscle cells.

To determine whether membrane free cholesterol affects calcium currents in vascular smooth muscle cells, whole-cell patch clamp recordings were made before and after cholesterol enrichment of cells by exposure to cholesterol-rich liposomes. Exposure to cholesterol-rich liposomes resulted in a gradual increase in the L-type current over 20 hours and a plateau (73 +/- 7% increase over basal) between 20 and 32 hours. This effect was associated with a rightward shift in the inactivation potential and a decrease in the sensitivity to (-)-PN-202-791, a dihydropyridine antagonist. There was no change in the maximum L-type current stimulated by (+)-PN-202-791, a dihydropyridine agonist. Liposome exposure caused a small, transient increase in the T-type current (peak effect, 20 minutes). We conclude that membrane cholesterol has important effects on the L-type calcium current in vascular smooth muscle cells, which is most likely due to an alteration in channel functional state rather than an increase in channel expression.

Animals↗
PubMed1992

Fast Na+ channels and slow Ca2+ current in smooth muscle from pregnant rat uterus.

Smooth muscle cells normally do not possess fast Na+ channels, but inward current is carried through two types of Ca2+ channels: slow (L-type) Ca2+ channels and fast (T-type) Ca2+ channels. Using whole-cell voltage clamp of single smooth muscle cells isolated from the longitudinal layer of 18-day pregnant rat uterus, depolarizing pulses, applied from a holding potential of -90 mV, evoked two types of inward current, fast and slow [8]. The fast inward current decayed within 30 ms, depended on [Na]o, and was inhibited by TTX (K0.5 = 27 nM). The slow inward current decayed slowly, was dependent on [Ca]o, and was inhibited by nifedipine. These results suggest that the fast inward current is a fast Na+ channel current, and that the slow inward current is a Ca2+ slow channel current. A fast-inactivating Ca2+ channel current was not evident. Thus, the ion channels which generate inward currents in pregnant rat uterine cells are TTX-sensitive fast Na+ channels and dihydropyridine-sensitive slow Ca2+ channels. The number of fast Na+ channels increased during gestation. The averaged current density increased from 0 on day 5, to 0.19 on day 9, to 0.56 on day 14, to 0.90 on day 18, and to 0.86 pA/pF on day 21. This almost linear increase occurs because of an increase in the fraction of cells which possess fast Na+ channels, and it is suggested that the fast Na+ current may be involved in spread of excitation. The Ca2+ channel current density also was higher during the latter half of gestation. These results indicate that the fast Na+ channels and Ca2+ slow channels in myometrium become more numerous as term approaches, and may facilitate parturition. Isoproterenol (beta-agonist) did not affect either ICa(s) or INa(f), whereas Mg2+ (K0.5 of 12 mM) and nifedipine (K0.5 of 3.3 nM) depressed ICa(s). Oxytocin had no effect on INa(f) and actually depressed ICa(s) to a small extent. Therefore, the tocolytic action of beta-agonists cannot be explained by an inhibition of ICa(s), whereas that of Mg2+ can be so explained. The stimulating action of oxytocin on uterine contractions is not due to stimulation of ICa(s). Figure 11 summarizes the possible mechanisms by which uterine contractility can be modulated. In contrast to vascular smooth muscle, neither ISO nor adenosine, which produce elevation of cyclic AMP, affected ICa and INa. Therefore, no arrow can be drawn between cA-PK/cG-PK and the Ca2+ slow channel.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine↗
PubMed1992

Interaction between stannous chloride and calcium channel blockers in frog neuromuscular transmission.

We have investigated the interactions between stannous chloride (SnCl2) and calcium (Ca) channel blockers on endplate potentials (e.p.p.) and on miniature endplate potentials (m.e.p.p.) to determine which type of channel (among L-, N-, and T-type) participates in the SnCl2-induced increase in Ca entry into motor nerve terminals. The e.p.p. amplitude augmented by 30 microM SnCl2 was decreased by cumulative addition of 10 microM CdCl2 or 0.5 microM omega-conotoxin but not by 10 microM NiCl2 or 5 microM nicardipine. The SnCl2 (30 microM)-induced rise in m.e.p.p. frequency in high-potassium medium was reduced by 0.5 microM omega-conotoxin but not by 5 microM nicardipine. These results suggest that activation of the N-type Ca channel is involved in the SnCl2-induced increase in Ca entry into the nerve terminals.

Animals↗