L-type Calcium Channel Blocker Nitrendipine Research Articles

Methods of activation and the role of calcium/calmodulin-dependent protein kinase II in the regulation of acetylcholine secretion in the motor synapses of mice

In electrophysiological studies of neuromuscular junctions of mice, it was demonstrated that evoked release of mediator triggered by calcium influx via P/Q calcium channels in the terminals remains unchanged in the presence of KN-62, a blocker of calcium/calmodulin-dependent protein kinase II (CaMKII). Disinhibition of L-type calcium channels by blockage of phosphatase calcineurin with cyclosporine A (CsA) causes an increase in the quantal content of endplate potentials (EPP’s QC), which can be prevented by the L-type calcium channel blocker nitrendipine, as well as by preliminary inhibition of CaMKII with KN-62. Thus, the acetylcholine (ACh) release is enhanced with involvement of activated CaMKII only after disinhibition of L-type calcium channels. When disinhibition of L-type calcium channels was induced by suppression of calcium-activated BK-type potassium channels with paxilline, an increase in EPP’s QC was also observed. The conclusion was drawn that in motor synapses of mice, calcium influx via P/Q-type calcium channels cannot provide selective activation of CaMKII to facilitate transmission. However, disinhibition of L-type calcium channels results in the activation of CaMKII, which is accompanied by a persistent increase in evoked ACh release.

Nanosecond electric pulse-induced calcium entry into chromaffin cells

Electrically excitable bovine adrenal chromaffin cells were exposed to nanosecond duration electric pulses at field intensities ranging from 2 MV/m to 8 MV/m and intracellular calcium levels ([Ca 2+] i) monitored in real time by fluorescence imaging of cells loaded with Calcium Green. A single 4 ns, 8 MV/m pulse produced a rapid, short-lived increase in [Ca 2+] i, with the magnitude of the calcium response depending on the intensity of the electric field. Multiple pulses failed to produce a greater calcium response than a single pulse, and a short refractory period was required between pulses before another maximal increase in [Ca 2+] i could be triggered. The pulse-induced rise in [Ca 2+] i was not affected by depleting intracellular calcium stores with caffeine or thapsigargin but was completely prevented by the presence of EGTA, Co 2+, or the L-type calcium channel blocker nitrendipine in the extracellular medium. Thus, a single nanosecond pulse is sufficient to elicit a rise in [Ca 2+] i that involves entry of calcium via L-type calcium channels.

Effects of calcium channel blockers on pentylenetetrazol drug discrimination in rats

The effects of the dihydropyridine L-type calcium channel blockers nitrendipine and nimodipine on the pentylenetetrazol (PTZ) drug discrimination, an operant model of anxiety, were investigated. Male Long–Evans rats were trained to discriminate PTZ (16 mg/kg, i.p.) from saline. Both nitrendipine (5.0–25 mg/kg, i.p.) and nimodipine (5.0–25 mg/kg, i.p.) partially substituted for the PTZ discriminative stimulus. However, pretreatment with nitrendipine (25 mg/kg, i.p.) or nimodipine (25 mg/kg, i.p.) produced no change in the PTZ dose-effect function. Rats were given a nutritionally balanced liquid diet containing 6.5% ethanol for 10 days. Rats selected the PTZ drug lever during withdrawal. Subchronic coadministration of nitrendipine (1.25–5.0 mg/kg, i.p., b.i.d.) with ethanol failed to dose-dependently reduce PTZ-lever responding, but it did reverse withdrawal signs. Acute administration of nitrendipine (5, 10, and 20 mg/kg, i.p.) produced marked suppression of lever responding, but it failed to significantly reduce levels of PTZ-lever responding. Although calcium channel blockers reduce signs of ethanol withdrawal, they also markedly reduce rates of behavior and produce no clear effects on anxiety-like behaviors induced by ethanol withdrawal.

Pharmacological study of signal transduction during stimulation of prothoracic glands from Manduca sexta

Cytosolic free calcium, [Ca 2+] i, measured in individual prothoracic gland cells of Manduca sexta with Fura-2 was increased by prothoracicotropic hormone, PTTH, and by mastoparan, a wasp venom peptide, activating G proteins. The effect on [Ca 2+] i of mastoparan and of PTTH was inhibited by cadmium and the antagonist of T-type calcium channels, amiloride, and not influenced by the L-type calcium channel blocker nitrendipine, suggesting that the same or similar plasma membrane channels are involved in the action of mastoparan and of PTTH. Pertussis toxin prevented the mastoparan-induced increase of [Ca 2+] i, whereas the effect of PTTH is not influenced by pertussis toxin. Intracellular addition of GDP-β-S failed to inhibit the PTTH-stimulated increase in [Ca 2+] i suggesting that G proteins are not involved in the stimulatory mechanism of PTTH.

Modulation of dihydropyridine-sensitive calcium channels in heart cells by fish oil fatty acids.

The highly unsaturated n-3 fatty acids from fish oils, eicosapentaenoic acid [EPA; C20:5 (n-3)] and docosahexanoic acid [DHA; C22:6 (n-3)], prevent the toxicity of high concentrations of the cardiac glycoside ouabain to isolated neonatal rat cardiac myocytes. Arachidonic acid [C20:4 (n-6)] lacks such protective action. The protective effect of the n-3 fatty acids is associated with their ability to prevent high levels of cytosolic free calcium from occurring in response to the ouabain. This in turn results, at least in part, from a 30% reduction in calcium influx rate induced by the n-3 fatty acids. This protective effect is simulated by nitrendipine, a dihydropyridine inhibitor of the L-type calcium channels in cardiac myocytes. Nitrendipine (0.1 mM) alone, however, inhibits myocyte contractility, as do verapamil (10 microM) and diltiazem (1.0 microM). EPA or DHA (5 microM) blocks the inhibitory effects of nitrendipine but not those of verapamil or diltiazem. Bay K8644, a known dihydropyridine agonist of L-type calcium channels, produces a ouabain-like effect that is also prevented by EPA or DHA. Specific binding of [3H]nitrendipine to intact myocytes is noncompetitively inhibited by EPA or DHA in a manner that reduces the number of high- and low-affinity binding sites (Bmax) and increases their affinities. The fish oil fatty acids prevent calcium overload from ouabain and Bay K8644. They also prevent a calcium-depleted state in the myocytes caused by the L-type calcium channel blocker nitrendipine. The protective effects of the n-3 fatty acids appear to result from their modulatory effects on nitrendipine-sensitive L-type calcium channels.