The γ-aminobutric acid (GABA)-ergic communication between the CNS and the anterior pituitary gland has been documented in numerous histochemical and biochemical studies but electrophysiological studies characterizing the GABAA receptor in the anterior pituitary are still lacking. In the present report we studied the GABA-induced current responses in cultured cells from the anterior pituitary gland of 6- to 10-day-old rats using the patch-clamp technique in the whole cell configuration. Fast application of GABA (100 µM) induced membrane currents in 90% of cells in 2-day-old cultures. The EC50 for GABA was 22.9 µM and the Hill coefficient was 1.8. The responses to GABA (10 µM) were inhibited by bicuculline (2 µM) to 14%, by picrotoxin (5 µM) to 21% and by zinc (10 µM) to 33%. Inhibition to 56% was observed with 6 µM strychnine. The GABA responses were sensitive to diazepam and pentobarbital. Half-maximal potentiation of responses to GABA (10 µM) was found with 1.0 µM diazepam and with 14.4 µM pentobarbital. The maximal potentiation of GABA responses was 222% for diazepam and 195% for pentobarbital. Pentobarbital (100 µM) did not induce any response in anterior pituitary cells in the absence of GABA. The application of GABA at concentrations 10 µM or higher, induced membrane currents that desensitized. Desensitization proceeded as a biexponential process with estimated fast and slow time constants which decreased with concentration. The responses to GABA (300 µM) desensitized to 93% with time constants of 1.4 and 5.3 s. Half-maximal desensitization was found with 13.4 µM GABA. The recovery of GABA responses from desensitization proceeded as a single-exponential process. Responses induced by 300 µM GABA, resensitized with a time constant of 20.8 s. We conclude that anterior pituitary cells possess GABAA receptors which exhibit the same pharmacological characteristics and desensitization kinetics but lower sensitivity to GABA as compared to those present in CNS neurones.

Keywords:
GABA, GABA receptors, Benzodiazepine, Patch clamp
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© 1995 S. Karger AG, Basel
1995
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