Ion-stimulated ATPase activity and NaCl uptake in the gills of freshwater mussels

Abstract

Microsomal membranes prepared from gills of the freshwater mussel Carunculina texasensis contain HCO3− ATPase, Cl−–HCO3− ATPase, and Na+–K+ ATPase activity. The HCO3− ATPase activity displays saturation kinetics with a Vmax of approximately 10 μM P/mg protein∙h−1 and an affinity of 5 mM HCO3−. The HCO3− ATPase can be stimulated by the addition of 1 mM Cl−, but it is inhibited by > 3 mM Cl− and by SCN−. The gill tissue ouabain-sensitive Na+–K+ ATPase activity represents approximately 1.5 μM P/mg protein∙h−1, which is low compared with the Mg2+ ATPase activity (12 μM P/mg protein∙h−1). We present preliminary evidence that the gills in freshwater mussels are a major site of Na+ and Cl− accumulation.