THE MECHANISM OF Ca2+ ACTION ON THE HEALINGOVER PROCESS IN MAMMALIAN CARDIAC MUSCLES: A KINETIC ANALYSIS

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Abstract
The effects of Ca2+ concentration and temperature on the recovery of membrane potential after investigating lesions using sucrose-gap technique in the guinea-pig papillary muscles were studied. At certain temperatures this recovery showed increased acceleration with increasing Ca2+ concentration. The relation between rate constant of the recovery and Ca2+ concentration was quite similar to that of the reaction between an enzyme and substrate. This relationship could be expressed by the equation Y = xn/(Km + xn), where Y is the normalized rate constant and x the Ca2+ concentration. The coefficient, n, was evaluated by performing Hill''s plot. The value of n largely changed between 1 and about 2 at 32.degree.-37.degree. C. The input resistance fell at the instant of formation of a lesion and started to rise with recovery of membrane potential. The resistance change after lesion formation was observed in the K-Tyrode''s solution in which Na+ was substituted with K+. The concentration-rate relationship of Ca2+ in the healing-over seems to indicate that Ca2+ binds to some molecules in the junctional membrane and produces a structural change of intercalated disc which brings about the healing-over. The large change of n suggests that Ca2+ has a cooperative action in the healing-over process, or alternatively that the state of membrane lipids has some effect on the process.

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