C-type natriuretic peptide (CNP) effects on intracellular calcium [Ca 2+] i in mouse gonadotrope-derived αT3-1 cell line

Abstract

C-type natriuretic peptide (CNP), the third member of the atrial natriuretic peptide family, acts via guanylyl cyclase containing GC-B receptors to stimulate cyclic guanosine 3′,5′ monophosphate (cGMP) accumulation in the gonadotrope-derived αT3-1 cell line and rat pituitary cells. This effect is inhibited by concomitant activation of the phospholipase C (PLC)-coupled gonadotrophin hormone-releasing hormone (GnRH) receptors in these cells. Since GnRH stimulates gonadotrophin secretion from gonadotropes by increasing the cytosolic Ca 2+ concentration ([Ca 2+] i) and natriuretic peptides have been found to influence PLC/Ca 2+ signalling in other systems, we have investigated whether CNP can alter basal or GnRH-stimulated changes in [Ca 2+] i in αT3-1 cells. In Ca 2+-containing medium, 10 −7 M CNP modestly, but significantly increased [Ca 2+] i over several min, but subsequently inhibited the elevation of [Ca 2+] i in response to 10 −7 M GnRH in both Ca 2+-containing and Ca 2+-free medium. This inhibitory effect was mimicked by 10 −6 M 8-Br-cGMP, but not by ANP, indicating mediation by cyclic GMP and the CNP-specific GC-B receptor. However, basal and GnRH-stimulated inositol (1,4,5) trisphosphate (Ins(1,4,5)P 3) generation were not measurably affected by CNP, and CNP failed to affect thapsigargin-induced capacitative Ca 2+ entry. Thus, it appears that the cross-talk between CNP and GnRH in these cells is reciprocal in that GnRH modulates CNP effects on cGMP generation, whereas, CNP modulates GnRH effects on Ca 2+ mobilisation.