CHARACTERIZATION OF ANGIOTENSIN-II BINDING TO GLOMERULI FROM RAINBOW-TROUT ONCORHYNCHUS-MYKISS ADAPTED TO FRESH-WATER AND SEAWATER

Specific binding of I-125-[Asn(1), Val(5)]-angiotensin II to isolated glomeruli of freshwater-adapted and seawater-adapted rainbow trout, On corhynchus mykiss, reached a plateau after 20 min at 10 degrees and wa s displaced by nonradiolabelled [Asn(1), Val(5)]-angiotensin II. Seawa ter adaptation increased the rate of dissociation of I-125-[Asn(1), Va l(5)]-angiotensin II from putative receptors. Competitive binding expe riments revealed a single population of high-affinity receptors with a K-D 0.3-0.4 x 10(-10) M, which was unchanged by seawater adaptation. Seawater adaptation did, however, reduce the density (B-max) of the bi nding sites, which may reflect down-regulation by the higher plasma co ncentration of angiotensin II in seawater-adapted trout. (C) 1994 Acad emic Press, Inc.