Ca2+-activated K+ channels in gonadotropin-releasing hormone-stimulated mouse gonadotrophs.
GnRH receptor activation elicits release of intracellular Ca(2+), which leads to secretion and also activates Ca(2+)-activated ion channels underlying membrane voltage changes. The predominant Ca(2+)-activated ion channels in rat and mouse gonadotrophs are Ca(2+)-activated K(+) channels. To establish the temporal relationship between GnRH-induced changes in intracellular [Ca(2+)] ([Ca(2+)](i)) and membrane current (I(m)), and to identify specific Ca(2+)-activated K(+) channels linking GnRH-induced increase in [Ca(2+)](i) to changes in plasma membrane electrical activity, we used single female mouse gonadotrophs in the perforated patch configuration of the patch-clamp technique, which preserves signaling pathways. Simultaneous measurement of [Ca(2+)](i) and I(m) in voltage-clamped gonadotrophs revealed that GnRH stimulates an increase in [Ca(2+)](i) that precedes outward I(m), and that activates two kinetically distinct currents identified, using specific toxin inhibitors, as small conductance Ca(2+)-activated K(+) (SK) current (I(SK)) and large (big) conductance voltage- and Ca(2+)-activated K(+) (BK) current (I(BK)). We show that the apamin-sensitive current has an IC(50) of 69 pM, consistent with the SK2 channel subtype and confirmed by immunocytochemistry. The magnitude of the SK current response to GnRH was attenuated by 17beta-estradiol (E(2)) pretreatment. Iberiotoxin, an inhibitor of BK channels, completely blocked the residual apamin-insensitive outward I(m), substantiating that I(BK) is a component of the GnRH-induced outward I(m). In contrast to its suppression of I(SK), E(2) pretreatment augmented peak I(BK). SK or BK channel inhibition modulated GnRH-stimulated LH secretion, implicating a role for these channels in gonadotroph function. In summary, in mouse gonadotrophs the GnRH-stimulated increase in [Ca(2+)](i) activates I(SK) and I(BK), which are differentially regulated by E(2) and which may be targets for E(2) positive feedback in LH secretion.
Waring
Dennis W
DW
Division of Endocrinology, Department of Internal Medicine, University of California, One Shields Avenue, Davis, California 95616, USA. dwwaring@ucdavis.edu
Turgeon
Judith L
JL
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D052681:Gonadotrophs / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology
D051036:Large-Conductance Calcium-Activated Potassium Channels; D010455:Peptides; D024681:Potassium Channels, Calcium-Activated; D051640:Small-Conductance Calcium-Activated Potassium Channels; D001030:Apamin; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; C064719:iberiotoxin; D002118:Calcium