Osmoregulation by gills of euryhaline crabs: molecular analysis of transporters

SYNOPSIS. The physiological mechanisms by which aquatic animals regulate the osmoconcentration of their body fluids remain unclear despite many excellent stud-ies of tissue and cell function. This review summarizes the current status of an ongoing molecular biological approach to investigating transporters and transport-related enzymes in ion-transporting gills of osmoregulating crustaceans. We have identified cDNAs coding for six candidate proteins in gills of the blue crab Calli-nectes sapidus and the green shore crab Carcinus maenas, including a Na1 1 K1-ATPase a-subunit, a V-type H1-ATPase B-subunit, a Na1/H1 exchanger, a Na1/ K1/2Cl2 cotransporter, two isoforms of carbonic anhydrase, and arginine kinase. Although our account is far from complete, examination of mRNA abundance by quantitative reverse transcription/polymerase chain reaction (RT/PCR) has iden-tified candidates that are preferentially expressed in gill epithelium, including the Na1 1 K1-ATPase a-subunit and Na1/H1 exchanger. The osmoregulatory response to salinity reduction includes enhanced mRNA expression of at least one form of carbonic anhydrase