Barium-induced LH release from chicken pituitary cells: synergism with phorbol ester.
Barium is known to elicit secretion in a number of cell systems. The mechanism of Ba2+ stimulation of LH release in cultured chicken pituitary cells was investigated in the present study. Barium-stimulated LH release was inhibited by extracellular Ca2+, indicating that Ba2+ does not act by stimulating Ca2+ entry. Simultaneous stimulation of the cells with Ba2+ and phorbol ester produced a synergistic response, similar to the synergism obtained with phorbol ester and treatments which increase cytosolic Ca2+. Both Ba2+-stimulated LH release and the synergism of Ba2+ with phorbol ester were inhibited by calcium channel blockers (Co2+, methoxyverapamil and nifedipine) and by calmodulin antagonists (trifluoperazine and chlorpromazine). These results indicate that the actions of Ba2+ are dependent on its entry through Ca2+ channels, and suggest that calmodulin activation is necessary for the synergism between Ba2+ and phorbol ester. Thus, synergism does not result from a direct effect of divalent cations on C-kinase.
Davidson
J S
JS
Department of Chemical Pathology, University of Cape Town Medical School, South Africa.
Wakefield
I
I
King
J A
JA
Millar
R P
RP
D000818:Animals; D001464:Barium / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D002645:Chickens; D004357:Drug Synergism; D007986:Luteinizing Hormone / Q000378:metabolism*; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors
D002121:Calcium Channel Blockers; D002147:Calmodulin; D001464:Barium; D007986:Luteinizing Hormone; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium