Roles of calcium and calmodulin in the mediation of acute and sustained GnRH-stimulated gonadotropin secretion from dispersed goldfish pituitary cells

被引:19
作者
Jobin, RM [1 ]
Neumann, CM [1 ]
Chang, JP [1 ]
机构
[1] UNIV ALBERTA, DEPT BIOL SCI, EDMONTON, AB T6G 2E9, CANADA
基金
加拿大自然科学与工程研究理事会;
关键词
D O I
10.1006/gcen.1996.0011
中图分类号
R5 [内科学];
学科分类号
1002 ; 100201 ;
摘要
The possible involvement of extracellular Ca2+ ([Ca2+](o)) in mediating the acute gonadotropin (GtH) response to salmon gonadotropin-releasing hormone (sGnRH) and chicken gonadotropin-releasing hormone-II (cGnRH-II) in goldfish was examined using dispersed pituitary cells in perifusion. Perifusion with Ca2+-deficient medium reduced the GtH responses to 5-min pulses of either GnRH, indicating the participation of [Ca2+](o) in acute GnRH action. Using a 10-min GnRH pulse application protocol, the dependence of the acute GtH responses to the two GnRHs on [Ca2+](o) entry through voltage-sensitive Ca2+ channels (VSCC) was examined using the dihydropyridine VSCC blocker nifedipine and the cation Co2+. Treatment with nifedipine consistently reduced the acute GtH response to either sGnRH or cGnRH-II. Similarly, perifusion with CoCl2, reduced the sGnRH-induced GtH release. In contrast to its effects on sGnRH, CoCl2 abolished the cGnRH-II-induced GtH release. These results indicate that [Ca2+](o) entry through VSCC participates in the acute GtH response to both native GnRHs; however, the cGnRH-II-stimulated acute release is relatively more dependent on [Ca2+](o) and VSCC functions than sGnRH-induced secretion. The involvement of calmodulin (CaM) in mediating GnRH action was also examined. Treatment with a CaM antagonist, calmidazolium, or with a Ca2+/CaM-dependent protein kinase II inhibitor, KN62, reduced GtH responses to sGnRH and cGnRH-II in 2-hr static incubation, but not in perifusion studies with dispersed goldfish pituitary cells using 5- or 10-min GnRH pulses. These results suggest that CaM-dependent mechanisms participate in mediating the long-term, but not the acute, GtH response to GnRH. Compared to sGnRH, cGnRH-II-induced GtH release was more sensitive to inhibition by KN62, indicating a higher degree of dependence of cGnRH-II action on CaM. These results extend our understanding of the differential involvement of [Ca2+](o) and CaM in mediating the short-term and long-term actions of the two native GnRH peptides on GtH release in goldfish, (C) 1996 Academic Press, Inc.
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页码:91 / 106
页数:16
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