Intestinal Bicarbonate Secretion in Marine Teleost Fish

University Of Miami, Coral Gables FL

Investigators

Abstract

Title: Intestinal bicarbonate secretion in marine teleost fish PI: Grosell, M. Institution: University of Miami Rosensteil School of Marine and Atmospheric Sciences This project investigates a novel aspect of salt and water balance in marine fish. Like most other vertebrates, marine fish maintain plasma osmolality ~ 300 mOsm which is much lower than that of the surrounding seawater (~1000 mOsm). Fish drink copious amounts of seawater to displace diffusive water loss to their environment. The imbibed seawater is desalinized in the esophagus after which Na+ and Cl- absorption in the intestine drives water uptake. Recent evidence suggests that a substantial portion of this intestinal Cl- uptake occurs via Cl-/ HCO3- exchange across the apical membrane of the intestinal epithelium and that this exchange process contributes to active transport of both ions. The PIs will aim at characterizing the cellular mechanisms of this Cl- uptake/HCO3- secretion system on isolated intestinal epithelia and to evaluate its contribution to overall Cl- and water absorption absorption also in intact animals. The high rates of HCO3- secretion results in highly alkaline intestinal fluid, which leads to CaCO3 precipitation in the intestine. One consequence of this precipitation is reduced osmolality of the intestinal fluids, which is hypothesized to aid water absorption. Manipulations of the precipitation through intestinal perfusion with salines of different composition are being performed to test this hypothesis. Although the substantial intestinal base secretion is not involved in dynamic regulation of acid-base balance it forms an important component of acid-base exchange with the environment. The PIs will investigate how variations in intestinal base secretion in response to different ambient salinities may be compensated by extra-intestinal acid extrusion. The research has a strong educational component and involves several undergraduate and graduate students.