Adaptations of the frog myocardium to conditions of natural hibernation: Morphofunctional changes

Abstract

The present study describes morphological and functional changes in the ventricular myocardium of Rana esculenta during hibernation., in comparison with active life. Contractile performance was analyzed in vitro on isolated ventricular trabeculae. Morphological studies were carried out with light and electron microscopy. In hibernating frogs, the myofibrillar apparatus appeared deteriorated and dispersed in an abundant paraplasma mainly consisting of glycogen granules. The accumulation of glycogen was confirmed by the intense staining with the PAS reaction. In accordance with morphological changes, tension development was reduced in trabeculae isolated from hibernating frogs. Whereas force-velocity relations did not show any difference between trabeculae from hibernating frogs and those from active frogs, significant differences were found in some parameters related to excitation-contraction coupling. In hibernating frog trabeculae, the relaxation phase was prolonged and the optimal interval of both transient and steady-state force-interval relations was lengthened. These changes, which point to a different calcium metabolism in cardiomyocytes from active and hibernating frogs, were in agreement with the lower activity of the Ca2+-ATPase observed in hibernating frog myocardium. © 1994 Taylor & Francis Group, LLC.