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1 Department of Neurology and 2 Second Department of Medicine, Technical University of Munich, D-81675 Munich, Germany
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.
high-voltage-activated calcium channels; histamine; calcium; patch clamp
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