[Electrophysiological and biochemical studies of GABA receptors in a primary cell culture of the pars intermedia of the porcine pituitary].

Using a primary culture of intermediate lobe (IL) we are investigating how GABA modulates stimulus-secretion coupling in the hypophysis. Two classes of GABA receptors have been described: GABA-A and GABA-B. We have characterised the GABA-A receptor using the patch clamp technique (Whole Cell Recording). GABA (10-100 microM) and isoguvacine (50 microM) a specific GABA-A agonist elicit an inward current with an equilibrium potential that coincides with Ecl-, this could explain the depolarising action of GABA-A agonists. When applying baclofen, the specific GABA-B agonist, no modifications of membrane potential were seen. Perfusion studies on alpha MSH release showed GABA (50 microM) and isoguvacine (50 microM) to potentiate Ba++-evoked secretion. The effects were antagonised by bicuculline and SR 95103, confirming GABA-A receptor action. Baclofen stereospecifically inhibited both basal and Ba++-evoked release. Together the results suggest the co-existence of the two classes of GABA receptors on the endocrine cells of the IL.