Aldosterone Modulates the Effect of Angiotensin II on the Electrical Properties of Rat Heart

Influence of aldosterone on the effect of angiotensin II on action potential duration and cardiac refractoriness was investigated in isolated ventricle of adult rats treated with aldosterone (2 microM/kg/d, intraperitoneally) for 48 h. Results indicated that angiotensin II (10-8 M) increases action potential duration at 50 and 90% of repolarization by 33 +/- 8.3% and 76 +/- 6.5% (p < 0.05), respectively (p < 0.05). Cardiac refractoriness and rheobase were increased by the peptide. These results contrast with those found in controls in which angiotensin II (10-8 M) reduces action potential duration at 50 and 90% of repolarization by 31.8 +/- 3.7% and 23 +/- 4.1% (p < 0.05), respectively, and decreases refractoriness. The increase in cardiac refractoriness elicited by angiotensin II on rats treated with aldosterone was reversed by verapamil (10-6 M) added to the bath. Moreover, verapamil significantly reduced the increment in action potential duration, at 90% repolarization, elicited by the peptide in presence of aldosterone, which suggests than an increase in inward calcium current is involved in the effect of angiotensin II. Aldosterone, however, did not influence effect of isoproterenol on action potential duration and refractoriness. Aldosterone modulates effect of angiotensin II on electrical properties of the heart. These findings indicate that effect of angiotensin II on electrical and probably other properties of the heart must be evaluated considering the presence or absence of aldosterone.