The effect of guanine nucleotides on [125I]-angiotensin binding in rat kidney cortex epithelial membranes

Pertussis toxin attenuates angiotensin II-induced vasoconstriction and inhibition of renin release

Angiotensin II can elicit cellular responses by 2 different receptor-dependent mechanisms: increase in intracellular calcium or inhibition of adenylate cyclase activity. The well-known inhibition of renin release from granulated cells of the kidney is thought to be mediated by an increase in intracellular calcium. However, the participation of the other possible pathway, i.e. inhibition of adenylate cyclase, has not been excluded. We studied this question by using the toxin from Bordetella pertussis, which inactivates the inhibitory coupling units Ni and thus permits to identify hormonal actions mediated through inhibition of adenylate cyclase. In isolated perfused kidneys from rats pretreated with pertussis toxin (2 micrograms/100 g i.v., single injection) the inhibition of renin release by angiotensin II (10(-11) to 10(-8) M) was significantly attenuated. In parallel, the vasoconstrictor response to angiotensin II was also diminished in these rat kidneys. The effect of pertussis toxin was apparent 3, 5 and 10 days after treatment, with a maximal effect at the fifth day. These data suggest that angiotensin II may exert the inhibitory effect on renin release in part through inhibition of adenylate cyclase in granulated cells of the kidney.

Inactivation of [125I]-angiotensin II binding sites in rat renal cortex epithelial membranes by dithiothreitol

Preincubation of renal epithelial membranes with DTT produced a dose-dependent inhibition of specific [125I]-angiotensin binding, with an IC50 of 1 mM and total loss of binding at 5-10 mM DTT. Inactivation of specific [125I]-angiotensin II binding by DTT was temperature sensitive; the t1/2 at 22 degrees was 6 min compared with 30 min at 4 degrees. A rapid inactivation rate was dependent on the presence of NaCl. In the presence of 120 mM NaCl the t1/2 for inactivation by DTT was 6 min and 33 min in the absence of NaCl. Protection against DTT inactivation was obtained by preincubating membranes with unlabelled angiotensin II greater than angiotensin I greater than renin substrate while the dipeptide, Ileu-His was only effective in protecting the binding site at high concentrations (10 mM). Preincubations with DTT (1 mM) caused a 43% decrease in Bmax from 217.0 +/- 39.5 to 123.7 +/- 30.9 fmol bound/mg protein while the KD was not significantly affected.

Location of [125I]-angiotensin II receptors on rat kidney cortex epithelial cells

Angiotensin II (AII) stimulates active Na+ extrusion from Na+ loaded renal cortex slices. Specific high affinity [125I]-AII binding sites in partially purified basolateral and brush-border epithelial membranes exhibit a KD of 0.88 nM and Bmax of 321.13 fmol mg-1 protein. Separation and purification of brush-border membranes yielded high affinity [125I]-AII binding sites with KD of 1.02 nM and Bmax of 56.6 fmol mg-1 protein. Angiotensin II receptors of the same affinity are present on renal cortex brush-border and basolateral membranes but a greater proportion are located on the latter. These receptors may be involved in the direct control of Na+ and water transport by AII.