An electrophysiological investigation of the characteristics and function of GABA_A receptors on bovine adrenomedullary chromaffin cells

The characteristics and function of γ-aminobutyric acidA (GABAA) receptors expressed on bovine chromaffin cells in culture have been investigated using patch-clamp techniques. In voltage-clamped whole-cells, locally applied GABA (100 μM) evoked a transmembrane chloride current which demonstrated outward rectification. The amplitude of such currents was reversibly suppressed by the GABAA receptor antagonists bicuculline, picrotoxin and RU5135, and enhanced by the general anaesthetic propanidid. Glycine (100 μM) and baclofen (100 μM) were ineffective as agonists. In support of a physiological role for GABA in the adrenal medulla, the co-existence of GABAA and nicotinic acetylcholine (ACh) receptors was demonstrated on whole cells and outside-out membrane patches. Ionophoretically applied GABA reduced the amplitude of depolarization and action potential discharge occurring in response to locally applied ACh (100 μM), but had no effect upon the underlying ACh-induced current. In addition, an excitatory action of GABA was demonstrated by recording action potential waveforms in cell-attached patches. The results are discussed in the context of a GABA-ergic regulation of catecholamine secretion.