Stimulatory Action of ?-Aminobutyric Acid on Catecholamine Secretion from Bovine Adrenal Chromaffin Cells Measured by a Real-Time Monitoring System

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Abstract
The present study was designed to evaluate the role of .gamma.-aminobutyric acid (GABA) in the secretory function of cultured chromaffin cells using the method of realtime monitoring. GABA evoked the secretion of catecholamines (CA) from adrenal chromaffin cells in a dose-dependent manner. Bicuculline 10-5 M inhibited the stimulatory action of GABA. Diazepam 5 .times. 10-6 and 2.5 .times. 10-5 M facilitated the secretory response evoked by 7 .times. 10-5 M GABA by 22% and 96%, respectively, which was antagonized by Ro 15-1788. This finding suggests that GABA-benzodiazepine receptor coupling can function in the secretion of CA from the adrenal chromaffin cells in a manner similar to that observed in the brain. GABA-evoked release of CA was reduced by 1 .mu.M nifedipine to 16% of control, suggesting the involvement of voltage-sensitive Ca2+ channels in the mechanisms of the CA-releasing action of GABA in these cells. From these findings, the involvement of GABAergic mechanisms in the regulation of adrenal medullary function can be proposed.