Distribution of γ-aminobutyric acid receptors in cultured adrenergic and noradrenergic bovine chromaffin cells

Abstract

Fluorescence imaging techniques for recording cytosolic [Ca2+]i from single chromaffin cells were used to characterize and discriminate between cell subpopulations containing γ‐aminobutyric acid (GABA)A and GABAB receptor subtypes. By combining this methodology with the immunoidentification of individual chromaffin cells using specific antibodies against tyrosine hydroxylase (TH), phenyl‐etanolamine‐N‐methyl transferase (PNMT), and glutamic acid decarboxylase (GAD) linked to different fluorescent probes, we have been able to ascribe single‐cell calcium responses to identified adrenergic and noradrenergic chromaffin cells. GAD enzyme is present in 30% of the chromaffin cell population, located primarily in adrenergic cells; 86% of GAD+ cells were also PNMT+. GAD expression was not correlated with the presence of GABA receptors. GABA‐responsive cells were found with equal frequency in the GAD+ and GAD− groups. However, the expression of GABA receptors was correlated with the adrenergic phenotype. [Ca2+]i responses to GABA were found more frequently in adrenergic than in noradrenergic cells. GABAA receptors are more evenly distributed; about 90% of GABA‐responsive cells have them. GABAB receptors have a more restricted distribution (present in 45% of responding cells). The coexpression of both GABAA and GABAB subtypes is the rule; only a minor subpopulation (about 12%) displays exclusively GABAB receptors. GABA receptor subtypes are distributed in a similar way when chromaffin cells are separated according to GAD+/GAD− or PNMT+/PNMT− classifications, with only minor differences. These data indicate that the intrinsic GABAergic system in the adrenal medulla is not designed as a paracrine model in which a group of cells specializes in transmitter synthesis and a different group serves as a specific target.