LOCALIZATION OF MESSENGER-RNA FOR THE PROTON PUMP (H-ATPASE) AND CL-()HCO3- EXCHANGER IN THE RAINBOW-TROUT GILL/

In situ hybridization was performed on sections of rainbow trout (Onco rhynchus mykiss) gill tissue using oligonucleotide probes complementar y to the mRNA of the 31-kilodalton subunit of the bovine renal V-type H+-ATPase or rat kidney Band 3 anion exchanger (Cl-/HCO3- exchanger). This was conducted in conjunction with measurements of whole-body net acid fluxes and blood acid-base status during imposed conditions of re spiratory acidosis (external hypercapnia) or metabolic alkalosis (NaHC O3 infusion). A positive hybridization signal for the H+-ATPase mRNA w as localized predominantly in lamellar epithelial cells and was less a pparent in cells associated with the filament or interlamellar regions . The H+-ATPase hybridization signal was enhanced during hypercapnic a cidosis concurrently with a marked increase in whole-body net acid exc retion. A positive hybridization signal for the Cl-/HCO3- exchanger mR NA was observed in epithelial cells on both the filament and lamella. During metabolic alkalosis induced by intra-arterial infusion of NaHCO 3, there was a marked increase in the Cl-/HCO3- exchanger mRNA hybridi zation signal in cells on both the filament and lamella that occurred concurrently with a decrease in net acid excretion. The results of thi s study support the existence of a V-type H+-ATPase and a Cl-/HCO3- ex changer in rainbow trout gill epithelial cells and demonstrate that al terations in gene expression for the pump-exchanger may be a significa nt mechanism underlying the altered rates of net acid equivalent excre tion during acid-base disturbances.