MARSHALL, W.S.; LYNCH, E.M.; HOWARD, J.A.; EPEGA, A.; COZZI, R.R.F.; St. Francis Xavier U.: CFTR expression patterns in a euryhaline teleost fish.
Cystic Fibrosis Transmembrane conductance Regulator (CFTR) in the euryhaline killifish Fundulus heteroclitus (kfCFTR) is an anion channel expressed in gill, opercular epithelium, brain and intestine. We established that CFTR was the channel responsible for anion secretion at the apical membrane of seawater (SW) chloride cells, combining Ussing style membrane chamber studies with patch clamp and immunocytochemistry. Apical membrane patches of SW chloride cells contained a cAMP activated an 8.1 pS anion channel that was blocked by NPPB and DPC. Xenopus oocytes expressing kfCFTR had cAMP activated, DPC sensitive Cl– current. Monoclonal antibody to kfCFTR carboxy terminus identified, by immunocytochemistry, that CFTR was in the apical membrane only of SW chloride cells but in basolateral membrane of fresh water (FW) chloride cells, implying selective apical vs. basolateral trafficking of CFTR in the two salinities. However, CFTR immunofluorescence did not change with short term cAMP activation of Cl– secretion. In brain, CFTR was locally expressed in paraventricular nuclei. Intestinal expression of CFTR was basolateral in most enterocytes and involved in ion absorption, but appeared in apical membrane of some cells. Activation by cAMP and Ca2+ evoked intestinal NaCl and fluid secretion that was inhibited by apical DPC but not DIDS, implicating CFTR in ion absorption and secretion in fish intestine. Supported by NSERC Canada.
