The receptor subtype mediating the action of angiotensin II on intracellular sodium in rat proximal tubules

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Abstract
An investigation was undertaken to explore the subtype of receptor involved in mediating the actions of angiotensin II on intracellular sodium content in suspensions of isolated proximal tubules of the rat. Intracellular sodium content of the proximal tubules was measured with 23Na n.m.r. spectroscopy and under these conditions basal sodium content of the tubular cells was 69.04±1.73 nmol mg−1 dry weight and the ATP levels, at 8.3±0.9 nmol ATP mg−1 protein, were consistent with active respiration by the tissue. In the presence of 10−4M PD123319, a selective non‐peptide AT2 receptor antagonist, intracellular sodium levels rose from steady state by 30% (Pn=7) within 10 min of exposure to angiotensin II 10−11M. Over the subsequent 30 min steady state levels were re‐established. Administration of angiotensin II 10−11M, in the presence of the selective AT1 receptor antagonist, losartan at either 10−6M (n=5) or 10−4M (n=6), was without effect on intracellular sodium levels, which were significantly different (P−5M, administered to the tubular suspension in the presence of 10−4M PD123319, decreased (Pn=6) intracellular sodium content by 16% in the first 5 min, but in the following 25 min returned to steady state levels. However, in the presence of losartan 10−4M, angiotensin II 10−5M had no effect on intracellular sodium content which was markedly different (P1 receptors. The intracellular mechanism underlying this effect remain to be investigated.