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

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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 a saturation kinetics with a Vmax of approximately 10 .mu.M P/mg protein .cntdot. 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 .mu.M P/mg protein .cntdot. h-1, which is low compared with the Mg2+ ATPase activity (12 .mu.M P/mg protein .cntdot. h-1). Preliminary evidence is presented that the gills in freshwater mussels are a major site of Na+ and Cl- accumulation.