CHANGES IN CALCIUM HANDLING IN ATROPHIC HETEROTOPICALLY ISOTRANSPLANTED RAT HEARTS

Atrophy of the rat heart induced by hemodynamic unloading after hetero topic transplantation is associated with impaired relaxation while sys tolic function remains normal when compared to the heart of the recipi ent animal. To identify possible underlying mechanisms for the above, we studied some aspects of membrane calcium handling using postextrasy stolic potentiation of contractions in the isolated right ventricular papillary muscle and in the left ventricle of the Langendorff-perfused heart. We also compared the alterations of the unloaded heart with th ose of overloaded hypertrophic hearts of rats with suprarenal aortic c onstriction. In the atrophic heart the degree of potentiation after on e extrasystole, considered to be proportional to the trans-sarcolemmal influx of Ca2+ during an action potential, was increased by 125 % whe n compared with recipient hearts. The rate of decay of potentiation wh ich reflects the fraction of activator Ca2+ recirculating in the cells via the sarcoplasmic reticulum, negatively correlated with the degree of potentiation, although its mean value was not significantly altere d. In hypertrophic hearts the decay of potentiation was faster when co mpared with the hearts of sham-operated animals, indicating a decrease d recirculating fraction of Ca2+. The data suggest that the relative i mportance of trans-sarcolemmal Ca2+ fluxes is increased both in cardia c atrophy and hypertrophy but their quantitative role in the control o f cardiac contraction might differ.