Effects of acetaldehyde on the isolated papillary muscle of diabetic rats.

The effects of acetaldehyde (ACA) were examined in isolated electrically driven papillary muscle preparations from normal and streptozotocin-treated diabetic rats. Muscles from diabetic rats developed greater tension than those from normal rats. In muscles from both groups, ACA caused concentration-dependent negative inotropic effects that were independent of cholinergic or purinergic mechanisms and were not attributable to nitric oxide (NO) release. ACA was three to five times more potent with regard to its negative inotropic effect in diabetic than in normal rat muscles. A propranolol-sensitive, sympathetically mediated positive inotropic effect occurred at certain concentrations. Decreasing [Ca2+]o from 2.7 to 0.5 mM reduced basal developed force to a significantly greater extent in muscles from normal rats than in those from diabetic rats. In low [Ca2+]o, concentration-response curves to CaCl2 in diabetic muscles were displaced to the left of that in normal muscles, suggesting that diabetic muscles are more sensitive to the positive inotropic effect of added CaCl2 at low [Ca2+]o, whereas at higher [Ca2+]o (> 1 mM), normal muscles developed more force in response to added CaCl2. ACA 10 and 30 mM more readily inhibited CaCl2-induced positive inotropic effect in normal than in diabetic muscles. Force-frequency curves, (negative staircase response) were recorded in both normal and diabetic muscles. In diabetic muscles, the curve exhibited a positive component at the lowest frequencies applied and was displaced to the right of that in normal muscle. ACA concentration-dependently inhibited force development, and diabetic muscles were more susceptible to the negative inotropic effect of ACA, when the stimulation frequency was increased.(ABSTRACT TRUNCATED AT 250 WORDS)