Relationship between nitric oxide- and calcium-dependent signal transduction pathways in growth hormone release from dispersed goldfish pituitary cells

• First study of NO and Ca2+ signalling interactions in fish pituitary hormone release.
• NO-induced GH release requires extra- and intracellular Ca2+, and CAMK-II.
• NO utilizes Ca2+ stores with TMB-8- and/or caffeine-sensitive channels.
• NO utilizes Ca2+ stores refilled by BHQ- and/or thapsigargin-inhibited CaATPases.
• Caffeine-induced GH release does not require NO.

Nitric oxide (NO) and Ca2+ are two of the many intracellular signal transduction pathways mediating the control of growth hormone (GH) secretion from somatotropes by neuroendocrine factors. We have previously shown that the NO donor sodium nitroprusside (SNP) elicits Ca2+ signals in identified goldfish somatotropes. In this study, we examined the relationships between NO- and Ca2+-dependent signal transduction mechanisms in GH secretion from primary cultures of dispersed goldfish pituitary cells. Morphologically identified goldfish somatotropes stained positively for an NO-sensitive dye indicating they may be a source of NO production. In 2 h static incubation experiments, GH release responses to the NO donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) were attenuated by CoCl2, nifedipine, verapamil, TMB-8, BHQ, and KN62. In column perifusion experiments, the ability of SNP to induce GH release was impaired in the presence of TMB-8, BHQ, caffeine, and thapsigargin, but not ryanodine. Caffeine-elicited GH secretion was not affected by the NO scavenger PTIO. These results suggest that NO-stimulated GH release is dependent on extracellular Ca2+ availability and voltage-sensitive Ca2+ channels, as well as intracellular Ca2+ store(s) that possess BHQ- and/or thapsigargin-inhibited sarcoplasmic/endoplasmic reticulum Ca2+-ATPases, as well as TMB-8- and/or caffeine-sensitive, but not ryanodine-sensitive, Ca2+-release channels. Calmodulin kinase-II also likely participates in NO-elicited GH secretion but caffeine-induced GH release is not upstream of NO production. These findings provide insights into how NO actions many integrate with Ca2+-dependent signalling mechanisms in goldfish somatotropes and how such interactions may participate in the GH-releasing actions of regulators that utilize both NO- and Ca2+-dependent transduction pathways.