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      Electrophysiological Characterization of GABA A Receptors in Anterior Pituitary Cells of Newborn Rats

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      S. Karger AG

      Patch clamp, GABA, GABA receptors, Benzodiazepine

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          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 GABA<sub>A</sub> 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 µ M) induced membrane currents in 90% of cells in 2-day-old cultures. The EC<sub>50</sub> for GABA was 22.9 µ M and the Hill coefficient was 1.8. The responses to GABA (10 µ M) were inhibited by bicuculline (2 µ M) to 14%, by picrotoxin (5 µ M) to 21% and by zinc (10 µ M) to 33%. Inhibition to 56% was observed with 6 µ M strychnine. The GABA responses were sensitive to diazepam and pentobarbital. Half-maximal potentiation of responses to GABA (10 µ M) was found with 1.0 µ M diazepam and with 14.4 µ M pentobarbital. The maximal potentiation of GABA responses was 222% for diazepam and 195% for pentobarbital. Pentobarbital (100 µ M) did not induce any response in anterior pituitary cells in the absence of GABA. The application of GABA at concentrations 10 µ M 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 µ M) desensitized to 93% with time constants of 1.4 and 5.3 s. Half-maximal desensitization was found with 13.4 µ M GABA. The recovery of GABA responses from desensitization proceeded as a single-exponential process. Responses induced by 300 µ M GABA, resensitized with a time constant of 20.8 s. We conclude that anterior pituitary cells possess GABA<sub>A</sub> receptors which exhibit the same pharmacological characteristics and desensitization kinetics but lower sensitivity to GABA as compared to those present in CNS neurones.

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          Author and article information

          S. Karger AG
          09 April 2008
          : 62
          : 2
          : 123-129
          Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
          126996 Neuroendocrinology 1995;62:123–129
          © 1995 S. Karger AG, Basel

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          Page count
          Pages: 7
          Cell Biology and Pharmacology of the Pituitary


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