Two endogenous gonadotropin-releasing hormones generate dissimilar Ca(2+) signals in identified goldfish gonadotropes.
Ca(2+) signals are involved in the signal transduction of neuroendocrine regulators. In goldfish, two endogenous gonadotropin-releasing hormones, salmon (s)GnRH and chicken (c)GnRH-II, control maturational gonadotropin secretion. Although considerable evidence suggests that sGnRH and cGnRH-II exert their activity on goldfish gonadotropes through a single population of receptors, differences in signal transduction mechanisms between these peptides have been demonstrated. We used ratiometric Fura-2 Ca(2+) imaging of single morphologically identified gonadotropes to quantitatively compare the Ca(2+) signals evoked by sGnRH and cGnRH-II. The amplitude and the rate of rise of sGnRH- and cGnRH-II-evoked Ca(2+) signals increased with concentration. At maximal concentrations, Ca(2+) signals generated by cGnRH-II rose significantly faster than those elicited by sGnRH, while other parameters such as the maximum amplitude, average Ca(2+) increase, and latency did not differ between the two peptides. Ca(2+) signals evoked by sGnRH or cGnRH-II were often spatially restricted to one part of the cell over the duration of the response. We provide a comprehensive account of the spatial and temporal aspects, including calculated kinetics, of GnRH-evoked Ca(2+) signals in single identified gonadotropes. This is the first report of quantified differences in Ca(2+) signals generated by two endogenous GnRH neuropeptides, which may act through the same receptor population in this cell type.
Johnson
J D
JD
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
Van Goor
F
F
Wong
C J
CJ
Goldberg
J I
JI
Chang
J P
JP
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D005260:Female; D005456:Fluorescent Dyes; D016257:Fura-2; D006054:Goldfish / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D010902:Pituitary Gland / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism*
D005456:Fluorescent Dyes; D007987:Gonadotropin-Releasing Hormone; C047717:LHRH, His(5)-Trp(7)-Tyr(8)-; D002118:Calcium; D016257:Fura-2