Functions of Ion Transporting Proteins NKA, NKCC and CFTR on the Intestinal Epithelia of Fundulus grandis during Osmotic Challenge

Abstract

The Gulf killifish (Fundulus grandis) is a euryhaline species distributed throughout marshes along the Gulf of Mexico, where they may be exposed to a broad range of salinities. This study investigates the cellular distribution and regulation of the ion‐transporting proteins, Na+/K+ ATPase (NKA), Na+/K+/Cl− cotransporter (NKCC), and chloride channel cystic fibrosis transmembrane conductance regulator (CFTR), in the intestine during osmotic challenges. NKA mRNA and protein levels were upregulated in both freshwater (FW) and seawater (SW); NKCC and CFTR mRNA and protein levels also showed variations due to FW or SW acclimation. NKA and CFTR were localized on the basolateral and apical or subapical membrane, respectively in both FW and SW, while NKCC localization was basolateral in FW and apical in SW. To determine the role of these proteins in ion regulation, we used Ussing Chambers, together with pharmacological blockers, and ion substitutions to measure the active Na+ or Cl− transport. NKA, NKCC, and CFTR appear to be implicated in a Cl− and Na+ secretion function in FW acclimated intestinal epithelia. However, in SW, there may be an ion absorption function facilitated by NKA and NKCC, while CFTR may be involved in acid/base regulation rather than Cl− secretion.