Neuroendocrine properties of human adrenocortical cells: GABA production and functional GABAB receptors in the NCI-H295R cell line

Abstract

The neurotransmitter GABA, well known for its functions in the central nervous system, is also present in peripheral endocrine tissues. GABAergic paracrine or autocrine signaling pathways have been found in the pancreatic islets, the adenohypophysis, and in steroid-producing organs like ovary and testis. In the present study, we describe elements of a GABAergic system in a human adrenocortical tumor cell line (NCI-H295R). Immunocytochemistry, Western blots and RT-PCR experiments showed that this cell line, a model system for the study of adrenocortical function, expresses glutamic acid decarboxylase (GAD) isoform 67, the biosynthetic enzyme for GABA. We furthermore demonstrated that these cells decarboxylate glutamate to GABA by an in-vitro assay. In addition, NCI-H295R cells express the GABAB(1a), GABAB(1e) and GABAB(2) subunits of the heterodimeric GABAB receptor as shown by RT-PCR and by immunostaining for the GABAB(2) subunit. According to our findings, GABAB(1e), a truncated splice variant of the GABAB(1) subunit which lacks the transmembrane and intracellular domains, is the predominant GABAB(1) transcript. The GABAB receptors we identified are functional since the GABAB-agonist baclofen decreased the low-voltage activated (T-type) calcium currents in whole-cell patch clamp experiments. In summary, our results show that GABA is produced by steroidogenic cells derived from the human adrenal cortex and may act on these cells in an autocrine manner. In addition, adrenocortical GABA may also reach the adrenal medulla via the vasculature and influence chromaffin cells which are responsive to GABA.