Pores in the Plasma Membranes of Myocardial Cells

Abstract

Heart muscle samples were collected from the right ventricles of twelve mature cattle and twelve pigs at slaughter and immediately prepared for electron microscopy by immersion in three different fixatives: 40% OsO4 dissolved in CCl4, 1.5% OsO4 in S collidine buffer, and in 2.5%. glutaraldehyde followed by 1.5%, OsO4. Some tissue from each animal was processed in each fixative and was embedded in either an epoxy resin or in a polyester resin. Sections were cut at 300 to 600 Å in thickness on a thermally advancing microtome, using glass and diamond knives, and were mounted on copper mesh grids. Uranyl acetate and lead citrate stains were used. Tissues were examined in an RCA, EMU-3F electron microscope.In both the cattle and pigs, some heart samples contained myocardial cells with plasma membranes which invaginated into the cells to form tubular appearing channels. These channels occurred in addition to the transverse sarcotubular system, and in addition to the pinocytotic vesicles. The basement membrane which surrounds myocardial cells did not extend into the invaginations, but bridged over their external apertures.