AJP - Cell Physiology, Vol 264, Issue 4 C1020-C1028, Copyright © 1993 by American Physiological Society

ARTICLES

Activation of protein kinase C increases Ca2+ sensitivity of secretory response of GH3 pituitary cells

A. A. Haymes and P. M. Hinkle
Department of Pharmacology, University of Rochester School of Medicine and Dentistry, New York 14642.

The effect of protein kinase C on the secretory response of GH3 pituitary cells to Ca2+ was investigated. Activation of protein kinase C with 100 nM 12-O-tetradecanoylphorbol 13-acetate (TPA) for 40 min reduced the rise in intracellular free calcium concentration ([Ca2+]i) stimulated by depolarization with high K+ but did not affect the threefold increase in prolactin secretion stimulated by 50 mM K+. Both [Ca2+]i and prolactin release were measured for control and TPA-treated cells over a range of [Ca2+]i values attained by adding the acetoxymethyl ester of 1,2-bis(2-aminophenoxy)-ethane -N,N,N',N'- tetraacetic acid (BAPTA/AM) to reduce [Ca2+]i or high K+ with or without BAY K 8644 to increase [Ca2+]i. Half-maximal prolactin secretion occurred at lower [Ca2+]i concentrations for cells treated with TPA (approximately 160 nM) than for control cells (approximately 270 nM), but the rate of secretion at high [Ca2+]i was the same. GH3 cells also secreted more prolactin in response to thyrotropin-releasing hormone (TRH) after protein kinase C activation, although TRH evoked a smaller Ca2+ transient. Fluorescence ratio imaging revealed that GH3 cells undergo spontaneous [Ca2+]i oscillations (4-12/min) and that TPA nearly abolishes [Ca2+]i oscillations as well as inhibits the increase in [Ca2+]i stimulated by depolarization. These results demonstrate that activation of protein kinase C increases the Ca2+ sensitivity of the secretory response in GH3 cells, causing up to a twofold increase in the rate of secretion at typical intracellular Ca2+ concentrations.

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				M. E. Freeman, B. Kanyicska, A. Lerant, and G. Nagy Prolactin: Structure, Function, and Regulation of Secretion Physiol Rev, October 1, 2000; 80(4): 1523 - 1631. [Abstract] [Full Text] [PDF]