Voltage-gated Ca2+currents in rat gastric enterochromaffin-like cells

Abstract

Enterochromaffin-like (ECL) cells are histamine-containing endocrine cells in the gastric mucosa that maintain a negative membrane potential of about −50 mV, largely due to voltage-gated K⁺currents [D. F. Loo, G. Sachs, and C. Prinz. Am. J. Physiol.270 ( Gastrointest Liver Physiol. 33): G739–G745, 1996]. The current study investigated the presence of voltage-gated Ca²⁺channels in single ECL cells. ECL cells were isolated from rat fundic mucosa by elutriation, density gradient centrifugation, and primary culture to a purity >90%. Voltage-gated Ca²⁺currents were measured in single ECL cells using the whole cell configuration of the patch-clamp technique. Depolarization-activated currents were recorded in the presence of Na⁺or K⁺blocking solutions and addition of 20 mM extracellular Ca²⁺. ECL cells showed inward currents in response to voltage steps that were activated at a test potential of around −20 mV with maximal inward currents observed at +20 mV and 20 mM extracellular Ca²⁺. The inactivation rate of the current decreased with increasingly negative holding potentials and was totally abolished at a holding potential of −30 mV. Addition of extracellular 20 mM Ba²⁺instead of 20 mM Ca²⁺increased the depolarization-induced current and decreased the inactivation rate. The inward current was fully inhibited by the specific L-type Ca²⁺channel inhibitor verapamil (0.2 mM) and was augmented by the L-type Ca²⁺channel activator BAY K 8644 (0.07 mM). We conclude that depolarization activates high-voltage-activated Ca²⁺channels in ECL cells. Activation characteristics, Ba²⁺effects, and pharmacological results imply the presence of L-type Ca²⁺channels, whereas inactivation kinetics suggest the presence of additional N-type channels in rat gastric ECL cells.