THE ACTION OF ANGIOTENSIN-II ON THE INTRACELLULAR SODIUM CONTENT OF SUSPENSIONS OF RAT PROXIMAL TUBULES

1. Intracellular sodium levels in isolated suspensions of rat proximal tubles were measured by Na-23 NMR spectroscopy and the effect of angi otensin II (AII) on these levels was recorded. 2. AII at 10(-11) M pro duced an increase in intracellular sodium content of appoximately 20% (P < 0.001) from the steady-state level 5 min after the addition of th e drug; intracellular sodium content then gradually returned to baseli ne levels over the subsequent 25 min. 3. Addition of AII at 10(-5) M r esulted in a significant 20 % decrease (P < 0.01) in the steadystate i ntracellular sodium level within 5 min. Again the effect was transient and steadystate intracellular sodium levels were re-established after 25 min. 4.Amiloride at 10(-4) M significantly attenuated the action o f AII at 10(-11) M (P < 0.0001) and inhibited the transient response t o AII at 10(-5) M (P < 0.01). When amiloride alone was added to the tu bular suspension, intracellular sodium content decreased significantly by 18-22% (P < 0.001), and addition of both the high and low doses of AII did not have any further effect on intracellular sodium level. 5. The actions of both concentrations of AII were unaffected by an inhib itor of endopeptidase-24.11, phosphoramidon at 10(-6) M, which suggest s that the transient action of AII was not due to the breakdown of AII by endopeptidase-24.11. 6. It is well known that AII at high doses in hibits and at low doses stimulates sodium transport across proximal tu bular epithelial cells. From the present data it is proposed that AII has a transient biphasic action on intracellular sodium content which may reflect the stimulation of the Na+-H+ exchanger.