Slowing effects of dopamine and calcium‐channel blockers on frequency of sodium spikes in rat pars intermedia cells
- 1 May 1982
- journal article
- research article
- Published by Wiley in The Journal of Physiology
- Vol. 326 (1), 201-211
- https://doi.org/10.1113/jphysiol.1982.sp014186
Abstract
Spontaneous discharge of action potentials (Na spikes) in cells isolated from rat pars intermedia was slowed or arrested by Co2+, Ni2+ or Mn2+, which block voltage-dependent Ca channels in these cells. The amplitude of persisting spikes was undiminished. The effects resembled those of dopamine [DA]. Action potential frequency decreased when the Ca2+ concentration was lowered to 0.1 mM and increased when the Ca2+ concentration was raised from this level to 1 or 2 mM, or when Ba2+ (2 mM) was introduced. These effects, together with those of Co2+, Ni2+ and Mn2+, are consistent with the possibility that Ca2+ participates in the regulation of spike discharge. Verapamil, methoxyverapamil (D600) and nifedipine reduced the amplitude of the individual Na spikes in concentrations that had little effect on voltage-dependent Ca channels. Action potential frequency was comparatively little affected by these drugs. K+ (15 mM) stimulated action potential frequency and this effect was suppressed by DA or Co2+. The effect which DA had of slowing spontaneous discharge, like the inhibitory effect on secretion, was blocked by metoclopramide. But otherwise the mechanism is unclear: DA blocked voltage-dependent Ca channels in some cells but not in most others. The effects of K+ and Ba2+ of eliciting spikes, the suppression of Na-spike discharge by Co2+ and related Ca-channel blocking cations, and the unspecific effects of the organic Ca-channel blockers, all, have implications for the use of these substances as tools to analyze stimulus-secretion coupling.This publication has 24 references indexed in Scilit:
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