ANGIOTENSIN-II AND ANGIOTENSIN-(1-7) EFFECTS ON FREE CYTOSOLIC SODIUM, INTRACELLULAR PH, AND THE NA-H+ ANTIPORTER IN VASCULAR SMOOTH-MUSCLE()

The aim of the present study was to define the effects of angiotensin II (Ang II) and Ang-(1-7) on free cytosolic Na+ (Na-i(+)), intracellul ar pH (pH(i)), and the Na+-H+ antiporter in cultured vascular smooth m uscle cells from rat aorta. Cells were loaded with either BCECF-AM or SBFI-AM for measurement of pH(i) and Na-i(+), respectively. Ang II (10 (-6) mol/L) caused a rapid rise in Na-i(+) followed by a progressive i ncrease that peaked at about 10 minutes (from 11+/-1.5 to 16+/-1.5 mmo l/L, P<.001), whereas Ang-(1-7) (10(-6) mol/L) did not affect Na-+(i) significantly (from 11.5+/-1.1 to 11.8+/-0.07 mmol/L). The effect of A ng II on Na-i(+) was concentration dependent (Delta Na-i(+), 5.1+/-0.9 , 3.8+/-0.6, 1.6+/-0.6, and 0.14+/-0.18 mmol/L with decreasing concent rations of 10(-6), 10(-7), 10(-8), and 10(-9) mol/L, respectively). An g II caused a brief acidification followed by an increase in pH(i) (fr om 7.34+/-0.03 to 7.43+/-0.03 after 10 minutes, P<.005), and Ang-(1-7) had no significant effect on pH(i) (from 7.23+/-0.03 to 7.23+/-0.03). To investigate whether pH(i) and Na-i(+) changes induced by Ang II we re due to cell Na+ entry via stimulation of the Na+-H+ antiporter, we pretreated cells with EIPA (25 mu mol/L) or ouabain (2.0 mmol/L). Ang II in the presence of ouabain caused a greater increase than that seen with ouabain alone (Delta Na-i(+), 13+/-1.5 versus 6.3+/-1.2 mmol/L, P<.0025). EIPA by itself decreased Na-i(+) and pH(i). After EIPA, Ang II failed to increase both Na-i(+) and pH(i), demonstrating that the N a+-H+ antiporter is responsible for the rises in Na-i(+) and pH(i) dur ing stimulation with Ang II. To further characterize the mechanism of Ang II action, we exposed cells to an Ang II type 1 receptor antagonis t (L-158,809, 10(-6) mol/L) or two different type 2 receptor antagonis ts (PD 123177 and CGP 421112A, 10(-6) mol/L). L-158,809 completely blo cked the rise in pH(i) caused by Ang II, whereas PD 123177 and CGP 421 112A did not. We conclude that Ang II increases both Na-i(+) and pH(i) , and both effects are mediated by stimulation of the Na+-H+ antiporte r. Ang-(1-7), by contrast, has no significant effect on Na-i(+), pH(i) , or the Na+-H+ antiporter. Stimulation of this antiporter by Ang II i s exerted through the type 1 receptor.