Numerical densities of intramembrane particles in the cardiac sarcolemma of normal and myopathic Syrian hamsters.

The purpose of this study was to examine the density of intramembrane particles in the cardiac sarcolemma of normal and myopathic Syrian hamsters in a search for a morphological marker of a putative membrane defect. Hereditary cardiomyopathy in hamsters is manifested by progressive multifocal skeletal and cardiac muscle necrosis. Although pharmacological and biochemical data suggest a molecular defect in the cardiac sarcolemma, there has been no morphological observation that would substantiate this suggestion. We quantified numerical densities of intramembrane particles in freeze-fractured sarcolemmal membrane protoplasmic and extracellular faces from the left and right ventricular myocardium of female 25-day-old hamsters of the U.M.-X 7.1 cardiomyopathic line compared with sex- and age-matched randomly bred Syrian hamsters. Intramembrane particle numerical densities significantly increased above control values in cardiomyopathic hamsters for protoplasmic face (from 2188 +/- 61 to 2454 +/- 89 microns-2 in left ventricle (P less than 0.025) and from 2255 +/- 83 to 2574 +/- 56 microns-2 in right ventricle (P less than 0.001]. There was no significant difference between intramembrane particle densities of normal and cardiomyopathic hamsters for extracellular face (707 +/- 45 and 687 +/- 49 microns-2 in the left ventricle and 742 +/- 41 and 746 +/- 28 microns-2 in the right ventricle). These results implicate an increase of protoplasmic face-associated integral proteins in the sarcolemmal membrane of cardiomyopathic hamster. The significance of this finding is not known. It may represent an adaptive change related to a molecular defect in the sarcolemmal membrane of cardiomyopathic hamster.