3H]Angiotensin II binding to basolateral membranes from rat proximal renal tubule: effect of sodium intake and captopril

Abstract

Basolateral membranes were prepared from rat renal cortex by density gradient centrifugation. Their purity was confirmed by electron microscopy and by marker enzyme enrichment. The basolateral membrane preparation was shown to be derived predominantly from the proximal renal tubule by measurement of hormone-stimulated adenylate cyclase; marked stimulation of adenylate cyclase was found with parathyroid hormone, but not with isoprenaline, antidiuretic hormone or calcitonin. A single class of specific high-affinity [3H]angiotensin II-binding site was identified in the basolateral membrane preparation which, after correction of results for tracer degradation, showed equilibrium dissociation constant of 0.23 nmol/l and binding site concentration of 485.8 fmol/mg protein. Binding sites for [3H]angiotensin II were measured in basolateral membranes prepared from rats fed diets with a low, normal or high sodium content. A trend of increased binding site density with reduced sodium intake was found which did not reach statistical significance. No effect on affinity was demonstrated. Treatment of rats on a low-sodium diet with captopril (500 mg/l drinking water) caused a significant reduction in binding site density; no effect on affinity was demonstrated. These findings suggest that the density of angiotensin II receptors at this site is altered by the activity of the renin-angiotensin system.