[Changes in the excitation contraction coupling in the myocardium of rabbits fed a cholesterol-containing diet]

It was of interest whether a hypercholesterolemia after feeding a diet containing 2 g cholesterol in sunflower oil per day during 12 weeks induces changes of the myocardiac cells of rabbits which must not necessarily be the consequence of a diminished bloodstream on account of coronary stenosis or the consequence of a lesion of the wall of the vessels. The contractile force and the indirectly measured shortening velocity of the isometrically working papillary muscle out of the left ventricle were not reliably changed. As a result of the feeding the isometric force rose after paired pulse stimulation and after a pause during the rhythmic action, although a considerable deposition of fat within the cells and disseminated necrosis in the myocardium could be observed. Because of the increasing loss of sodium into sodium-free solution in parallel with an increasing sodium content of the myocardium it has been concluded that the permeability of the cell membrane for this ion should be elevated. Furthermore it is assumed that the activation of the ionic pumps is elevated which is recognizable from a higher positive inotropic action of both the application of strophanthine and the substitution of NaCl by LiCl. But it seems that one elevation could not completely compensate the other one. The mean value of the velocity of relaxation related to the isometric force was increased. It has been postulated that after the diet rich in cholesterol and sunflower oil the cardiac cell shows a retarded restitution of the contraction during the interval between beats and elevated content of calcium. This may be one of the causes for the observed necrosis besides the ischemic component of the injurant feeding.