Meeting Abstract

121-6  Tuesday, Jan. 7 11:45 – 12:00  Aquaporin Expression in the Gill of Japanese Medaka ELLIS, LV*; BOLLINGER, RJ; WEBER, HM; MADSEN, SS; TIPSMARK, CK; University of Arkansas; University of Arkansas and University of Southern Denmark; University of Arkansas; University of Southern Denmark; University of Arkansas lvellis@uark.edu

Aquaporins (Aqps) are theorized to regulate cell volume homeostasis through water and solute transport. This study examined Japanese medaka (Oryzias latipes ) gill Aqp1 and Aqp3 expression and localization in response to salinity challenges and osmoregulatory hormones, cortisol, and prolactin (PRL). Expression of aqp3 was elevated in ion-poor water (IPW) compared to normal freshwater (FW), and very low transcript levels were observed in seawater (SW). Aqp3 protein levels decreased with acclimation to SW. Aqp1 expression however, was unaffected by salinity. PRL stimulated aqp3 mRNA in ex vivo gill incubation experiments in both a dose and time-dependent manor, but was unaffected by cortisol. In contrast, aqp1 was unaffected by both PRL and cortisol. The combination of cortisol and PRL had an additive stimulatory effect on aqp3 , while aqp1 remained unchanged. Confocal microscopy showed Aqp3 in the periphery of epithelial cells in gill filaments and co-localized at low intensity with Na⁺,K⁺-ATPase in ionocytes. While Aqp1 was found in most filament epithelial cells at low intensity and red blood cells, no immunoreactivity to Aqp3 or Aqp1 were found in the epithelial cells of the gill lamellae. We suggest that both Aqps contribute to cellular volume regulation in the gill epithelium and that Aqp3 is essential under hypo-osmotic conditions, while expression of Aqp1 is constitutive.