Abstract

Angiotensin II (A-II) is known to potentiate ischemic dysfunction during ischemia, but the mechanisms involved are not completely established. We examined the effects of A-II on intracellular calcium concentration ([Ca⁺⁺]_i) and cell contracture caused by metabolic inhibition in isolated adult rabbit ventricular myocytes. [Ca⁺⁺]_i was assessed by flow cytometry, using the Ca⁺⁺-sensitive fluorescent probe, fluo-3. After 90 min of exposure to 2 mM cyanide (CN) and 0 glucose, there was a significant increase in myocyte [Ca⁺⁺]_i. This increase was slightly augmented in the presence of 100 nM A-II. In the presence of partial Na⁺/K⁺ ATP pump inhibition ([K⁺]_o = 0.8 mM), there was a more significant increase in [Ca⁺⁺]_i associated with exposure to CN+A-II vs. CN alone. Similar results were obtained with CN plus 2-deoxyglucose, and the effect of A-II was inhibited by 10 μM 5-(N-ethyl-N-isopropyl)amiloride. Myocytes exposed to 2 mM CN and 0 glucose gradually developed contracture over a 3-hr period. Addition of 100 nM A-II significantly (P < .01) enhanced loss of rod shape morphology during 3 hr of CN exposure. Partial inhibition of the Na⁺ pump by exposure to 0.8 mM K⁺ had no effect on myocyte survival in the absence of CN, but augmented the harmful effect of A-II on cell contracture caused by CN exposure. This effect of A-II was completely reversed by the addition of 1 mM amiloride, a Na⁺/H⁺ exchange inhibitor. We conclude that A-II directly enhances cell injury during CN exposure in isolated rabbit ventricular myocytes. We postulate that this effect of A-II is mediated by stimulation of Na⁺/H⁺ exchange with resultant increased [Na⁺]_i and subsequent [Ca⁺⁺]_i loading, possibly via reverse Na⁺/Ca⁺⁺ exchange.