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Electrophysiological analysis of the sensitivity to calcium in ventricular muscle from alloxan diabetic rats


Basic Research in Cardiology 81(5): 489-496
Electrophysiological analysis of the sensitivity to calcium in ventricular muscle from alloxan diabetic rats
The effects of acute and chronic alloxan diabetes on the transmembrane electrical activity of rat heart papillary muscle were investigated. The action potential duration (APD) appeared markedly prolonged in all diabetic papillary muscles, as compared to normal. This prolongation of ADP, with no difference in the resting potential (RP), resulted from both a lengthening of the complex time course plateau and a slower rate of repolarization. APD0 (at 0 mV) and ADP10 (+10 mV from RP) increased, respectively, an average of 50% and 24% in the acute, and 72% and 98% in the chronic diabetics as compared to control, whereas .ovrhdot.Vmax and overshoot (OS) were unchanged. Varying Ca 10 between 0.5 and 3.5 mM did not induce any change in the RP of either control or diabetic papillary muscles. Conversely, there were differences, within and between groups, in the amplitude of the OS and in .ovrhdot.Vmax, depending on the [Ca]o concentration. In particular, OS and .ovrhdot.Vmax of acute diabetics were markedly reduced at 1.5 mM. This reduction was maintained at concentrations of [Ca]o lower than 1.5, attesting to the greater sensitivity of both acutely and chronically diabetic muscles to a decrease in external calcium. Cd, a Ca-channel blocker, reduced in diabetics the duration of both the complex plateau and the repolarization phase, suggesting that a Ca inward current was maintained throughout these two phases. Direct evidence for eludicating the mechanism(s) of the observed APD change in diabetics will be obtained only by transmembrane current analysis.

Accession: 005349412

PMID: 3800847

DOI: 10.1007/bf01907755

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