Loading...
2 results
Search Results
Now showing 1 - 2 of 2
- Ca2+-Calmodulin regulation of testicular androgen production in Mozambique tilapia (Oreochromis mossambicus)Publication . Martins, Rute S. T.; Fuentes, J.; Almeida, O. G.; Power, Deborah; Canario, Adelino V. M.The Ca2+-Calmodulin (CaM) signaling pathway has previously been shown to be involved in the regulation of teleost fish ovarian steroidogenesis. However, a putative role of CaM in testicular steroidogenesis and potential targets has not been examined. To examine whether basal steroidogenesis is modulated by Ca2+ and CaM levels in the testis of Mozambique tilapia (Oreochromis mossambicus) we have incubated testicular fragments in vitro under different conditions and analyzed steroid output. Calcium-free medium with or without EGTA did not affect testicular basal 11-ketotestosterone (11-KT) and testosterone (T) secretion. However, addition of 80 lM the CaM inhibitor W7 significantly reduced basal 11-KT, T and androstenedione secretion. Interestingly, the decreased androgen production by 80 lM of W7 was accompanied by increased 11-desoxicortisol output and by the activation of cortisol synthesis in the testis, the latter undetected in untreated tissues. However, production of 17,20a-dihydroxy-4-pregnen- 3-one was unaltered by W7. This suggests that C17,20 desmolase, 21-hydroxylase and possibly 11bhydroxysteroid dehydrogenase are targets for CaM. In addition, androgen production was also found to be regulated by the level of cAMP since incubations with forskolin (FK) significantly increased 11-KT and T output. A cross-talk between the cAMP and Ca2+-CaM signaling pathways was detected since W7 administration also decreased FK stimulated androgen production. Altogether, these data show that both basal and cAMP stimulated androgen levels were modulated by intracellular Ca2+-dependent CaM and that possibly Ca2+-CaM determines the shift in steroidogenesis from C21 steroids to androgens.
- Water absorption and bicarbonate secretion in the intestine of the sea bream are regulated by transmembrane and soluble adenylyl cyclase stimulationPublication . Carvalho, Edison Samir Mascarelhas; Gregorio, Silvia; Power, Deborah; Canario, Adelino V. M.; Fuentes, J.In the marine fish intestine luminal, HCO3 - can remove divalent ions (calcium and magnesium) by precipitation in the form of carbonate aggregates. The process of epithelial HCO3 - secretion is under endocrine control, therefore, in this study we aimed to characterize the involvement of transmembrane (tmACs) and soluble (sACs) adenylyl cyclases on the regulation of bicarbonate secretion (BCS) and water absorption in the intestine of the sea bream (Sparus aurata). We observed that all sections of sea bream intestine are able to secrete bicarbonate as measured by pH–Stat in Ussing chambers. In addition, gut sac preparations reveal net water absorption in all segments of the intestine, with significantly higher absorption rates in the anterior intestine that in the rectum. BCS and water absorption are positively correlated in all regions of the sea bream intestinal tract. Furthermore, stimulation of tmACs (10 lM FK? 500 lM IBMX) causes a significant decrease in BCS, bulk water absorption and short circuit current (Isc) in a region dependent manner. In turn, stimulation of sACs with elevated HCO3 - results in a significant increase in BCS, and bulk water absorption in the anterior intestine, an action completely reversed by the sAC inhibitor KH7 (200 lM). Overall, the results reveal a functional relationship between BCS and water absorption in marine fish intestine and modulation by tmACs and sAC. In light of the present observations, it is hypothesized that the endocrine effects on intestinal BCS and water absorption mediated by tmACs are locally and reciprocally modulated by the action of sACs in the fish enterocyte, thus fine-tuning the process of carbonate aggregate production in the intestinal lumen.