AJP - Endocrinology and Metabolism, Vol 266, Issue 1 E39-E43, Copyright © 1994 by American Physiological Society

ARTICLES

Rat Prl and TSH secretion are regulated differently by K(+)-channel blockers

X. Wang, T. Inukai, M. A. Greer and S. E. Greer
Department of Medicine, Oregon Health Sciences University, Portland 97201.

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.

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