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Ca 2+ ‐Dependent K + Currents Induced by Muscarinic Receptor Activation in Guinea Pig Adrenal Chromaffin Cells
Author(s) -
Ohta Toshio,
Ito Shigeo,
Nakazato Yoshikazu
Publication year - 1998
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1998.70031280.x
Subject(s) - muscarine , apamin , chemistry , charybdotoxin , muscarinic acetylcholine receptor , chromaffin cell , biophysics , reversal potential , inositol , fura 2 , channel blocker , patch clamp , acetylcholine , membrane potential , endocrinology , medicine , calcium , adrenal medulla , receptor , biochemistry , cytosol , biology , catecholamine , enzyme , organic chemistry
The characteristics of the outward current ( I out ) induced by muscarine were examined by using the whole‐cell patch‐clamp technique with a K + ‐containing pipette solution in combination with fura‐2 microfluorometry in guinea pig chromaffin cells. Muscarine caused a transient increase in the cytosolic Ca 2+ concentration ([Ca 2+ ] i ) and activated an I out with a reversal potential close to a K + equilibrium potential. Under symmetric K + conditions, muscarine produced a transient inward current and an increase in [Ca 2+ ] i at −60 mV. At −15 mV, apamin and charybdotoxin, respective SK and BK channel blockers, decreased the I out but scarcely affected the [Ca 2+ ] i response to muscarine. Muscarine produced an I out and an increase in [Ca 2+ ] i even after a removal of external Ca 2+ and in the presence of Co 2+ , indicating that these responses are mediated by Ca 2+ release from intracellular stores. The I out evoked by the Ca 2+ release was much smaller than that evoked by the voltage‐dependent Ca 2+ influx, even when similar [Ca 2+ ] i changes assessed by fura‐2 microfluorometry occurred. Inositol 1,4,5‐trisphosphate (InsP 3 ) applied intracellularly and the photolysis of caged InsP 3 each evoked current changes similar to those induced by muscarine. These results indicate that the I out evoked by muscarinic stimulation is mediated by Ca 2+ ‐dependent K + channels (probably BK and SK channels), which are activated by Ca 2+ released from intracellular Ca 2+ stores in guinea pig chromaffin cells.