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Ca 2+ ‐dependent K + current and exocytosis in responses to caffeine and muscarine in voltage‐clamped guinea‐pig adrenal chromaffin cells
Author(s) -
Ohta Toshio,
Wakade Arun R.,
Nakazato Yoshikazu,
Ito Shigeo
Publication year - 2001
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.1471-4159.2001.00502.x
Subject(s) - muscarine , chemistry , caffeine , chromaffin cell , cyclopiazonic acid , catecholamine , biophysics , apamin , adrenal medulla , endocrinology , medicine , membrane potential , calcium , biochemistry , muscarinic acetylcholine receptor , endoplasmic reticulum , biology , receptor , organic chemistry
We characterized changes in membrane currents and the cytosolic Ca 2+ concentration, [Ca 2+ ] i , in response to caffeine, and compared them with those in response to muscarine using the perforated patch‐clamp technique and fura‐2 microfluorimetry in guinea‐pig adrenal chromaffin cells. Catecholamine release from single voltage‐clamped cells was monitored with amperometry using carbon microelectrodes. Caffeine produced a transient outward current ( I out ) at holding potentials over − 60 mV, increasing in amplitude with increasing the potentials. It also evoked a rapid increase of [Ca 2+ ] i at all potentials examined. The current‐voltage relation revealed that the activation of K + channels was responsible for the I out evoked by caffeine. Both current and [Ca 2+ ] i responses were reversibly abolished by cyclopiazonic acid, an inhibitor of Ca 2+ ‐pump ATPase. At − 30 mV, the caffeine‐induced I out , but not [Ca 2+ ] i , was partly inhibited by either charybdotoxin or apamin. In the majority of cells tested, caffeine induced a larger I out but a smaller [Ca 2+ ] i increase than muscarine. Caffeine and muscarine increased catecholamine release from voltage‐clamped single cells concomitant with the transient increase of [Ca 2+ ] i , and there was a positive correlation between them. These results indicate that caffeine activates Ca 2+ ‐dependent K + channels and catecholamine secretion due to the release of Ca 2+ from internal stores in voltage‐clamped adrenal chromaffin cells of the guinea‐pig. There seems to be a spatial difference between [Ca 2+ ] i increased by Ca 2+ release from caffeine‐sensitive stores and that released from muscarine (inositol 1,4,5‐trisphosphate)‐sensitive ones.