R. Boualibenazzouz et al., ESTRADIOL MODULATION OF GNRH-STIMULATED LH-RELEASE IN RAT ANTERIOR-PITUITARY-CELLS - INVOLVEMENT OF DIHYDROPYRIDINE-SENSITIVE CALCIUM CHANNELS, Neuroendocrinology, 57(6), 1993, pp. 1161-1170
Although enhancement of GnRH-stimulated luteinizing hormone (LH) relea
se by estradiol (E2) has been established, it is not known at what sta
ges of the process of transduction E2 acts. We investigated the releas
e of LH in response to GnRH and to Bay K 8644, an activator of L-type
calcium channels, in a culture of pituitary cells obtained from ovarie
ctomized females, these cells having being treated or not with E2 (OVX
+ E2 and OVX). We studied the effects of D600, an antagonist of T- an
d L-type calcium channels, and PN 200-110, an antagonist of L-type cal
cium channels. The effects of the latter were studied in protein kinas
e C-depleted cells in order to investigate the possible phosphorylatio
n of these channels. D600 caused a decrease in GnRH-stimulated LH rele
ase in OVX and OVX + E2 cells. However, this decrease was greater in O
VX + E2 cells, suggesting that at least one type of calcium channels m
ay be involved as a result of treatment with E2. We confirmed the invo
lvement of L-type calcium channels in the action of GnRH since the GnR
H-stimulated LH release was enhanced in the presence of Bay K 8644 in
OVX cells. Bay K 8644 alone increased basal LH in a dose-dependent man
ner only in OVX + E2 cells. PN 200-110 induced a decrease of GnRH-stim
ulated LH release only in OVX + E2 cells. These results suggest that L
-type calcium channels are activated in E2-treated cells. The dose-dep
endent decrease caused by PN 200-110 in OVX + E2 cells disappeared in
the OVX + E2 PKC-depleted cells. This result was confirmed with Bay K
8644 and suggests a phosphorylation of dihydropyridine-sensitive calci
um channels by protein kinase C.