Role of the invertebrate electrogenic 2Na+/1H+ antiporter in monovalent and divalent cation transport.
In recent years, an electrogenic 2Na+/1H+ antiporter has been identified in a variety of invertebrate epithelial brush-border membranes of gut, kidney and gill tissues. The antiporter differs significantly in its physiological properties from the electroneutral 1Na+/1H+ antiporter proposed for vertebrate cells. In all invertebrate cells examined, the antiporter displayed a 2:1 transport stoichiometry, responded to an induced transmembrane potential and exhibited a high binding affinity for the divalent cation Ca2+, which acted as a competitive inhibitor of Na+ transport. A monoclonal antibody specific for the crustacean electrogenic antiporter inhibited 2Na+/1H+ exchange, but was without effect on Na(+)-dependent D-glucose transport. Immunoreactivity was localized at hepatopancreatic brush-border and vacuolar membranes, antennal gland coelomosac podocytes and posterior gill epithelial cells-all locations were published reports described unique cation exchange kinetics. Significant fractions of Ca2+ transport into invertebrate cells across brush-border membranes occurred by an electrogenic, amiloride-sensitive exchange process, probably by the 2Na+/1H+ antiporter, and this transport was markedly inhibited by exogenous zinc and cadmium. A recently identified electroneutral, amiloride-sensitive, hepatopancreatic epithelial basolateral Na+/H+ antiporter was uninfluenced by the brush-border monoclonal antibody, exhibited an apparent 1:1 transport stoichiometry and possessed a minimal divalent cation specificity. Calcium transport at this epithelial pole occurred by the combination of a Ca2+/Na+ antiporter, an ATP-dependent Ca(2+)-ATPase and a verapamil-sensitive calcium channel. These crustacean brush-border and basolateral transporters may play significant roles in calcification and heavy metal detoxification.
Ahearn
G A
GA
Department of Zoology, University of Hawaii at Manoa, Honolulu 96822.
Zhuang
Z
Z
Duerr
J
J
Pennington
V
V
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism*; D002414:Cations, Monovalent / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004064:Digestive System / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D005880:Gills / Q000378:metabolism; D007448:Invertebrates / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D009928:Organ Specificity; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*
D002413:Cations, Divalent; D002414:Cations, Monovalent; D017923:Sodium-Hydrogen Exchangers; D002118:Calcium