Temperature modulates the osmosensitivity of tilapia prolactin cells.

In euryhaline fish, prolactin (Prl) plays an essential role in freshwater (FW) acclimation. In the euryhaline and eurythermal Mozambique tilapia, , Prl cells are model osmoreceptors, recently described to be thermosensitive. To investigate the effects of temperature on osmoreception, we incubated Prl cells of tilapia acclimated to either FW or seawater (SW) in different temperature (20, 26 and 32°C) and osmolality (280, 330 and 420 mOsm/kg) combinations for 6 h. Release of both Prl isoforms, Prl and Prl, increased in hyposmotic media and were further augmented with a rise in temperature. Hyposmotically-induced release of Prl was inhibited at 20°C. In SW fish, mRNA expression of and showed direct and inverse relationships with temperature, respectively. In SW-acclimated tilapia Prl cells incubated in hyperosmotic media, Prl receptors, and , and the stretch-activated Ca channel, , were inhibited at 32°C, suggesting the presence of a cellular mechanism to compensate for elevated Prl release. Transcription factors, , , , , , and , known to regulate and , were also downregulated at 32°C. Our findings provide evidence that osmoreception is modulated by temperature, and that both thermal and osmotic responses vary with acclimation salinity.