Regulatory role of gamma-aminobutyric acid (GABA) in catecholamine release from adrenal medulla

我们利用原代培养的牛肾上腺嗜铬细胞研究了γ -氨基丁酸（GABA）在肾上腺髓质释放儿茶酚胺（CA）中的作用。1. GABA诱导单层培养的牛肾上腺染色质细胞释放CA，并通过GABA受体促进乙酰胆碱（ACh）诱导的CA释放。苯二氮卓类药物和戊巴比妥增强了GABA的作用。2. GABA引起钙吸收增加，钙释放增加。疼痛诱导的^<45>钙摄取被GABA加性增强，而缬草碱（低浓度）诱导的^<45>钙摄取被GABA加性增强。3. 以不可渗透的阴离子或蔗糖替代细胞外的C1^-，以时间相关的方式改变gaba诱发的^<45>钙摄取和Ca释放：突然用蔗糖替代细胞外的C^-，增强gaba诱发的Ca释放，而长期低C1^-中剂量治疗，则降低gaba诱发的Ca释放和^<45>钙摄取。4. GABA增加了双氧醇荧光，反映了嗜铬细胞的去极化。此外，GABA引起细胞质Ca^<2+> ([Ca^<2+>]i)的增加，以quin2评估。gaba诱导的去极化和[Ca^<2+>]i的升高与^<45>的Ca摄取和Ca释放密切相关。基于这些结果，我们得出结论，GABA通过电压门控Ca^<2+>通道引起Ca^<2+>的内流，这是通过C1^依赖机制的去极化的结果。这进而引发[Ca^<2+>]i升高，导致GABA自身胞外释放Ca，并促进GABA对刺激诱发的Ca释放的调节。

We investigated the role of gamma-aminobutyric acid (GABA) in catecholamine (CA) release from adrenal medulla using a primary culture of bovine adrenal chromaffin cells. 1. GABA elicited CA release from monolayer cultures of bovine adrenal chromaffin cells, and facilitated acetylcholine (ACh)-evoked CA release via GABA receptor. Benzodiazepines and pentbarbital enhanced the action of GABA. 2. GABA caused an increase in ^<45>Ca uptake associated with CA release. Ach-induced ^<45>Ca uptake was additively enhanced by GABA, whereas veratridine (at low concentration)- evoked ^<45>Ca uptake was more than additively enhanced by GABA. 3. GABA-evoked ^<45>Ca uptake and CA release were modified by replacing extracellular C1^- by impermeable anion or sucrose in a time-related fashion: sudden replacement of extracellular C^- by sucrose enhanced GABA-evoked CA release whereas long-term treatment with low C1^- medium reduced GABA-evoked CA release and ^<45>Ca uptake. 4. GABA increased bis-oxonol fluorescence, reflecting a depolarization of chromaffin cells. Furthermore, GABA caused an increase in cytosolic Ca^<2+> ([Ca^<2+>]i), assessed by quin2. GABA-induced depolarization and rise of [Ca^<2+>]i were well correlated with ^<45>Ca uptake and CA release.Based on these results, we concluded that GABA causes an influx of Ca^<2+> through voltage- gated Ca^<2+> channels as a consequence of depolarization via C1^--dependent mechanism. This, in turn, elicited [Ca^<2+>]i rise leading to an exocytotic release of CA by GABA itself and to an facilitatory modulation by GABA of stimulation-evoked CA release.