Meeting Abstract
Na/K ATPase on the basolateral membrane of gill cells actively transports Na+ from the cell interior to blood, creating the electrochemical gradient that drives secondary active transporters in the apical membrane for Na+ influx. H-ATPase on apical membranes is hypothesized to facilitate Na+ uptake. Factors such as temperature and salinity affect the activities of enzymes. It has been postulated that the activities of proteins such as Na/K ATPase and H-ATPase are reduced in cold acclimated poikiotherms to conserve energy. We hypothesized that both Na/K ATPase and H-ATPase activity would be lower in cold vs. warm acclimated fish, and that fish acclimated to higher salinities would have lower activities of both enzymes. Fish were acclimated to 20°C, 12.5°C, and 5°C for 28 days, and Na/K ATPase and H-ATPase activity measured. Na/K-ATPase activity from fish at 5°C was 2.79±0.07 while that from fish at 20°C was 1.62±0.08 µmoles/mg protein/hr (p <0.05), 72% greater. In contrast, H-ATPase activity was 0.0±0.06 at 5°C and 0.48±0.05 µmoles/mg protein/hr at 20°C (p<0.01). High salinity (130.53 mM vs 0.60 mM) resulted in decreased Na/K-ATPase activity (1.40±0.11 vs 1.95±0.17µmoles/mg protein/hr; p<0.05). Surprisingly, H-ATPase activity increased in fish acclimated to higher salinity (0.00±0.05 vs. 0.58±0.10 µmoles/mg protein/hr). We find that: 1) Na/K ATPase activity increases in cold acclimated fish to compensate for loss of activity caused by temperature; 2) H-ATPase is unlikely to contribute to Na absorption under some conditions 3) the concept of “channel arrest” may not apply to Na absorption in gill epithelium.
