Analysis of the Inner and Outer Environment of Sarcolemma in Cardiac Muscle Cells

Abstract

The peripheral envelope of cardiac myocytes interfaces their inner and outer environment to perform its specific functions. We used stereological analysis of electron micrographs to estimate the association of plasmalemmal structures with their neighbors. Left ventricular papillary muscles of adult rats were dissected and processed for electron microscopy. Uniform random images of the sarcolemma were taken from longitudinal sections at 50,000× magnification and analyzed using a cycloid grid. Intersections of cycloids with structures occurring in the 100 nm wide layer adjacent to the surface sarcolemma of myocytes were counted and the relative occurrence of individual structures was calculated. The cytoplasm dominated at caveolae and nexuses. Myofibrils reached the highest relative occurrence at desmosomes and nexuses, while mitochondria and sarcoplasmic reticulum at the plain plasmalemma (PPL) and at the mouths of t-tubules (MTT). Other small cytosolic structures occurred rarely and only at the PPL. The cavity of caveolae was almost completely covered by the basal lamina (BL). The desmosomes were equally covered with BL and by neighbor myocytes. The PPL was covered by BL 10x more than by myocytes. The MTTs were covered 10x more by BL than by external fluid. The nexuses, by definition, connected neighbor myocytes. Endothelium or collagen approached the surface of myocytes very rarely. The stereologic analysis of the peripheral envelope of cardiac myocytes revealed how specifically is the sarcolemma structured within its inner and outer environment and provided its quantitative characterization.Supported by APVV-0721-10, VEGA 2/0116/12, VEGA 2/0203/11, by FaF UK/29/2013.