Meeting Abstract

87.8  Thursday, Jan. 7  Chloride cell differentiation in Mozambique tilapia: roles of prolactin, growth hormone and cortisol BREVES, J.P.*; WATANABE, S.; HELMS, R.; KANEKO, T.; HIRANO, T.; GRAU, E.G.; Univ of Hawaii; Univ of Tokyo; Univ of Hawaii; Univ of Tokyo; Univ of Hawaii; Univ of Hawaii breves@hawaii.edu

A series of hypophysectomy (Hx) and hormonal replacement therapy experiments were conducted to characterize the regulation of branchial chloride cell (CC) differentiation in Mozambique tilapia (Oreochromis mossambicus). In tilapia, a recently identified Na⁺/Cl^– cotransporter (NCC) is specific to freshwater (FW)-type CCs, while seawater (SW)-type CCs specifically express a Na⁺/K⁺/2Cl^– cotransporter (NKCC). NCC and NKCC therefore provide markers for the presence of CCs tied to ion absorptive and secretive processes, respectively. First, we assessed the effect of Hx on mRNA levels of these ion transporters in the gill during acclimation to both FW and SW. In both salinities, Hx markedly reduced NCC gene expression when compared with sham-operated controls; no effect of Hx on NKCC was evident. In FW, NCC expression was restored in Hx fish by treatment with ovine prolactin (oPRL) alone or in combination with cortisol; there was no effect of cortisol alone. In contrast, expression of NKCC was stimulated by cortisol, an effect that was attenuated by co-treatment with oPRL. In SW, cortisol and ovine growth hormone showed no clear actions on NKCC expression. Taken together, our findings suggest that the hyperosmoregulatory actions of PRL derive from its ability to simultaneously stimulate NCC expression (ion absorption) and inhibit NKCC (ion extrusion) and that the recruitment of SW-type CCs does not necessarily require pituitary control in this euryhaline tilapia. Supported by NSF (IOB05-17769), USDA (2008-35206-18785) and the Pauley Foundation.