Long-term Angiotensin-Converting Enzyme Inhibition With Fosinopril Improves Depressed Responsiveness to Ca 2+ in Myocytes From Aortic-Banded Rats

BACKGROUND: We have previously shown that long-term ACE inhibition with fosinopril prolongs survival and improves ventricular function despite persistent severe left ventricular pressure overload in ascending aortic-banded rats with left ventricular hypertrophy during the transition from compensation to failure. METHODS AND RESULTS: To study the cellular mechanism of the effects of long-term ACE inhibition on the modification of the transition to failure in pressure-overload hypertrophy, we measured simultaneous intracellular Ca2+ transients and myocyte shortening in isolated left ventricular myocytes from fosinopril-treated aortic-banded rats (n = 9), untreated aortic-banded rats (n = 9), and normal age-matched control rats (n = 10). Fosinopril therapy was begun 6 weeks after banding and was continued until week 21 after banding, when the animals were killed. Collagenase-dissociated myocytes loaded with indo 1-AM were paced at 3 Hz at 36 degrees C and superfused at Ca2+o of 0.6, 1.2, and 3.0 mmol/L. In myocytes from untreated aortic-banded rats, peak systolic Ca2+i was higher than in control myocytes, and the relationship between myocyte shortening and Ca2+i was depressed relative to control myocytes, implicating impaired responsiveness to Ca2+. Long-term fosinopril treatment improved both myocyte shortening and the relationship of shortening to Ca2+i (P < .05 versus myocytes from untreated aortic-banded rats). Maximal Ca(2+)-activated force was depressed in chemically skinned left ventricular fibers from untreated aortic-banded hypertrophied rats relative to age-matched controls but not in the fosinopril-treated aortic-banded rats. CONCLUSIONS: Long-term ACE inhibition improves responsiveness to Ca2+ in the presence of normalization of maximal Ca(2+)-activated force in aortic-banded rats subjected to persistent pressure overload. This may contribute to the favorable effects whereby ACE inhibition modifies the transition from compensated hypertrophy to failure.