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J. Biol. Chem., Vol. 281, Issue 35, 25231-25240, September 1, 2006

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Essential Role of G Protein-gated Inwardly Rectifying Potassium Channels in Gonadotropin-induced Regulation of GnRH Neuronal Firing and Pulsatile Neurosecretion^*

From the Endocrinology and Reproduction Research Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892-4510

Activation of the luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor (LHR) in cultured hypothalamic cells and immortalized GnRH (gonadotropin-releasing hormone) neurons (GT1–7 cells) transiently stimulates and subsequently inhibits cAMP production and pulsatile GnRH release. The marked and delayed impairment of cAMP signaling and episodic GnRH release in GT1–7 cells is prevented by pertussis toxin (PTX). This, and the LH-induced release of membrane-bound G_s and G_i3 subunits, are indicative of differential G protein coupling to the LHR. Action potential (AP) firing in identified GnRH neurons also initially increased and then progressively decreased during LH treatment. The inhibitory action of LH on AP firing was also prevented by PTX. Reverse transcriptase-PCR analysis of GT1–7 neurons revealed the expression of G protein-gated inwardly rectifying potassium (GIRK) channels in these cells. The LH-induced currents were inhibited by PTX and were identified as GIRK currents. These responses indicate that agonist stimulation of endogenous LHR expressed in GnRH neurons activates GIRK channels, leading to suppression of membrane excitability and inhibition of AP firing. These findings demonstrate that regulation of GIRK channel function is a dominant factor in gonadotropin-induced abolition of pulsatile GnRH release. Furthermore, this mechanism could contribute to the suppression of pituitary function during pregnancy.

Received for publication, April 4, 2006 , and in revised form, June 20, 2006.

^* This work was supported by the Intramural Research Program of the National Institutes of Health, NICHD. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ On leave from the Dept. of Pharmacology, Catholic University of the Sacred Heart, 00168 Rome, Italy.

² To whom correspondence should be addressed: Endocrinology and Reproduction Research Branch, Bldg. 49, Rm. 6A-36 NICHD, National Institutes of Health, Bethesda, MD 20892. Tel.: 301-496-2136; Fax: 301-480-8010; E-mail: lazar{at}mail.nih.gov.

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