Activity changes in gill ion transporter enzymes in response to salinity and temperature in fathead minnows (Pimephales promelas).

Fathead minnows, Pimephales promelas, are found throughout the continental United States in waters in which salinity can change with tides and temperatures vary seasonally. They have been used extensively in studies of environmental toxicology and are commercially important. In a very recent study in our labs RNA Seq was used to assemble transcriptomes from the gills of fatheads acclimated to either 5° or 22 °C. By comparison with published genomes, transcripts were identified for a number of ion transporters, ion channels, and signal molecule receptors, as well as enzymes that generate ammonia. H-ATPase and Na/K-ATPase activities were measured in supernatants of gill homogenates from fish acclimated to water sodium concentrations of 1.6, 3.1 or 124 mM sodium. As the water sodium concentration increased, in vitro activities of Na/K-ATPase activity and gill glutamate dehydrogenase activity decreased while H-ATPase activity increased. In a second series of experiments minnows were acclimated to 5 °C, 12.5 °C or 22 °C. In vitro activity of Na/K-ATPase decreased but activities of H-ATPase and glutamate dehydrogenase increased as temperature increased in gill membranes. These data do not support a primary role for apical H-ATPase in sodium influx under all conditions but do suggest a role for glutamate dehydrogenase production of ammonium to act as a counter-ion for sodium uptake by NHE-3.