Abstract
GABA is known to produce a depolarization or secretion in adrenal medullary (AM) cells of various species. However, whether the GABAergic system is intrinsic or extrinsic in the adrenal medulla is ambiguous. Thus, we addressed this issue using immunological techniques. The immunoblotting and immunohistochemistry revealed that GAD, a GABA synthesizing enzyme, was present in rat AM cells, but not adrenal cortical cells. VGAT, a vesicular GABA transporter, was also found in the rat adrenal medulla. The fractionation study with bovine adrenal medulla showed that GAD and VGAT were recovered in a crude membrane fraction, but not in a chromaffin granule fraction, suggesting GABA is stored in synaptic-like microvesicles, but not chromaffin granules. Perfusion of a GABA-containing solution in the rat AM cells loaded with Fura-2 resulted in an increase in Ca 2+ signal in some, but not all, of AM cells that responded to electrical stimulation. The maximum response of Ca 2+ signal evoked by both electrical stimulation and GABA did not differ from that elicited by electrical stimulation alone. This result suggests that GABA did not produce an inhibition of membrane excitability through a shunt effect. The immunoblot showed that GABA receptors in rat AM cells consisted of at least α 1, α 3, and γ 2 subunits. The results suggest that GABA functions as a paracrine or autocrine in rat AM cells [J Physiol Sci. 2006;56 Suppl:S216]
