AJP - Endocrinology and Metabolism, Vol 243, Issue 1 68-E73, Copyright © 1982 by American Physiological Society
Calcium channel and prolactin release in rat clonal pituitary cells: effects of verapamil
S. Ozawa and N. Kimura
Effects of verapamil on membrane electrical properties and prolactin
release were studied in a rat anterior pituitary cell line GH3.
Thyrotropin-releasing hormone (TRH), Ba2+, and high concentration of K+
enhance the release of prolactin from GH3 cells. These stimulatory actions
on prolactin release were inhibited by adding 10(-4) M verapamil to the
bathing mediums. The maximum rate of rise of the Ca action potential was
reduced to 17% of the control by addition of 10(-4) M verapamil. Ba2+
caused a sustained membrane depolarization because Ba2+ goes through the Ca
channels and blocks the development of the delayed rectification. This
effect of Ba2+ was also inhibited by verapamil. Verapamil suppressed both
the Na+ and outward K+ currents in addition to the Ca2+ current. The
suppressive effect of verapamil on the voltage-sensitive Ca current is
probably responsible for the inhibition of TRH- and high K+-stimulated
prolactin release because the suppression of the Na+ and outward K+
currents does not inhibit the stimulatory actions of these secretagogues.
