Nitrendipine and omega-conotoxin modulate gonadotropin release and gonadotrope [Ca2+]i.
We have examined the pharmacology of the voltage-sensitive Ca2+ channels (VSCCs) that mediate gonadotropin secretion from primary cultures of rat pituitary cells, stimulated by either cell depolarization or by binding of gonadotropin-releasing hormone (GnRH). We also measured single-cell [Ca2+]i transients using fura-2 in gonadotropes identified by a reverse hemolytic plaque assay employing an antiserum to luteinizing hormone (LH). Cell depolarization evoked by either 50 mM K+ or 30 microM veratridine induced 2- to 6-fold increases in gonadotropin secretion over basal levels. GnRH caused 6- to 20-fold increases in follicle-stimulating hormone (FSH) and LH secretion, respectively, with maximal stimulation at 100 nM GnRH. K(+)- or GnRH-induced FSH release was largely prevented by co-incubation with 1 mM CdCl. Tetrodotoxin (TTX, 5 microM) prevented the veratridine-, but not the K(+)- or GnRH-induced, stimulation of FSH secretion. Nitrendipine (Ntd, 1 microM) produced 35-50% inhibition (NS) of both FSH and LH release stimulated by either 50 mM K+ or 100 nM GnRH. Ntd also inhibited the K(+)-induced [Ca2+]i rise (greater than 90%), as well as the secondary, plateau phase of the GnRH-induced elevation of [Ca2+]i (100% inhibition). Omega-conotoxin (omega-CgTx, 100 nM) partially suppressed FSH and LH release (NS) due to both K+ (33% each) and GnRH (44% and 18%, respectively). omega-CgTx showed variable effects on [Ca2+]i transients evoked by K+ or GnRH ranging from clear inhibition to no effect. We conclude that influx of extracellular Ca2+ is one of several fundamental events underlying the depolarization- or receptor-activated release of LH and FSH, and that this influx can be inhibited by dihydropyridine-sensitive ('L') Ca2+ channels. Two classes of L-channels may exist in gonadotropes, that differ in their sensitivity to omega-CgTx.
Blotner
M
M
Department of Pharmacological, University of Chicago Pritzker School of Medicine, IL 60637.
Shangold
G A
GA
Lee
E Y
EY
Murphy
S N
SN
Miller
R J
RJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects*; D007986:Luteinizing Hormone / Q000378:metabolism*; D008564:Membrane Potentials; D009568:Nitrendipine / Q000494:pharmacology*; D010456:Peptides, Cyclic / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012636:Secretory Rate / Q000187:drug effects; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D010456:Peptides, Cyclic; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D020866:omega-Conotoxin GVIA; D009568:Nitrendipine; D002118:Calcium