AJP - Endocrinology and Metabolism, Vol 253, Issue 5 E591-E594, Copyright © 1987 by American Physiological Society
GRF elevates cytosolic free calcium concentration in rat anterior pituitary cells
C. Schofl, J. Sandow and W. Knepel
Department of Pharmacology, University of Freiburg im Breisgau, Federal Republic of Germany.
The effect of human growth hormone-releasing factor (GRF) on intracellular
free calcium concentration ([Ca2+]i) was examined in rat anterior pituitary
cells. The [Ca2+]i was monitored directly by means of the intracellularly
trapped fluorescent indicator, fura-2. GRF rapidly elevated [Ca2+]i,
reaching a new plateau within approximately 30 s. The half-maximally
effective concentration of GRF was approximately 130 pM. GRF produced a
maximal increase in [Ca2+]i by approximately 120 nM. The GRF (2 nM)-induced
elevation of [Ca2+]i was abolished by removal of extracellular calcium
(Ca2+ omitted, 2 mM EGTA). The GRF (2 nM)-caused rise in [Ca2+]i was
largely reduced in the presence of the calcium channel blockers Mg2+ (31.2
mM) or nifedipine (1 microM). An increase in [Ca2+]i by approximately 60 nM
was elicited by the addition of prostaglandin E2 (1 microM), which can
stimulate growth hormone secretion independent of GRF receptors. These data
indicate that GRF elevates the [Ca2+]i, possibly in somatotrophs; this
GRF-induced increase in [Ca2+]i may depend on an influx of extracellular
Ca2+, largely through Mg2+- and nifedipine-sensitive calcium channels.
