Rat Prl and TSH secretion are regulated differently by K(+)-channel blockers.
All four different K(+)-channel blockers [tetraethylammonium (TEA), a nonselective K(+)-channel blocker; tolbutamide, an ATP-sensitive K(+)-channel blocker; quinine and 4-aminopyridine, both primarily voltage-dependent K(+)-channel blockers] stimulated prolactin (Prl) secretion by acutely dispersed anterior pituitary cells but had no effect on thyroid-stimulating hormone (TSH) secretion. TEA stimulated Prl secretion in a dose-dependent manner between 1 microM and 20 mM, but even as high as 20 mM, TEA did not induce TSH secretion. Valinomycin (2 microM), a K+ ionophore, inhibited both basal and TEA-induced Prl secretion. TEA-stimulated Prl secretion was abolished by using a Ca(2+)-depleted medium or adding 10 microM dopamine. TEA did not reverse the inhibitory effect of dopamine on thyrotropin-releasing hormone-induced Prl secretion. Our data indicate that K+ channels may play a role in the secretion of adenohypophysial hormones that is idiosyncratic for each hormone. Differences in the role of K+ channels may reflect differences between the various pituitary cell types in plasma membrane ion channel composition, membrane potential, or the mechanism of exocytosis.
Wang
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Department of Medicine, Oregon Health Sciences University, Portland 97201.
Inukai
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Greer
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Greer
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D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003470:Culture Media / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology; D008297:Male; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013972:Thyrotropin / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
D003470:Culture Media; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D014634:Valinomycin; D019789:Tetraethylammonium; D011388:Prolactin; D013972:Thyrotropin; D002118:Calcium; D004298:Dopamine