GABAA receptor-mediated increase of cytosolic Ca2+ in isolated bovine adrenal chromaffin cells.
We have studied the effects of GABA on cytosolic free Ca2+ concentration ([Ca2+]i) as a means of investigating the role of GABA in adrenal catecholamine (CA) secretion. It was demonstrated that GABA caused an elevation of [Ca2+]i via the GABAA receptor in a concentration-dependent manner, which was well correlated with an increase of 45Ca uptake, an increase of CA release and a depolarization of chromaffin cells assessed with bis-oxonol fluorescence. Since the GABA-induced rise of [Ca2+]i was absolutely dependent on the presence of extracellular Ca2+ and partly sensitive to nifedipine, at least one entry route for Ca2+ facilitated by GABA via a voltage-sensitive Ca2+ channel was suggested. When extracellular Cl- was lowered, GABA-induced CA release, depolarization, and rise of [Ca2+]i were all markedly enhanced. It is possible that GABA plays a modulatory role in the regulation of adrenal CA secretion as a facilitatory modulator.
Kitayama
S
S
Department of Pharmacology, Hiroshima University, School of Dentistry, Japan.
Morita
K
K
Dohi
T
T
Tsujimoto
A
A
D000311:Adrenal Glands / Q000187:drug effects / Q000378:metabolism*; D000634:Aminoquinolines; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002417:Cattle; D002712:Chlorides / Q000494:pharmacology; D002837:Chromaffin Granules / Q000187:drug effects / Q000378:metabolism*; D002838:Chromaffin System / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000634:Aminoquinolines; D015220:Calcium Channels; D002712:Chlorides; D005456:Fluorescent Dyes; D005680:gamma-Aminobutyric Acid; C035739:Quin2; D002118:Calcium