CALCIUM RESPONSIVENESS IN CANINE PACING-INDUCED HEART-FAILURE

The specific lesion(s) and potential compensatory alterations of excit ation-contraction coupling in heart failure are not clear in detail. W e therefore subjected five dogs to 2-5 weeks of rapid ventricular paci ng until heart failure developed. Data obtained from these live dogs w ith pacing-induced heart failure were compared to data from six health y controls. Under anesthesia, in situ steady state responses of region al contractile function to intracoronary calcium infusion were establi shed. Maximal calcium-activated regional contractile function in dogs with heart failure was 46% less than in controls; calcium sensitivity was unchanged [pCa(50) 2.55 +/- 0.31 v 2.82 +/- 0.17 (+/-S.D.)]. Our d ata point to a decrease in maximal calcium-activated force and an unch anged calcium sensitivity if an unchanged calcium transient is assumed , or a compensatory increase in calcium sensitivity of failing myocard ium if a decreased calcium transient is assumed. (C) 1998 Academic Pre ss