STRUCTURE AND STAINING CHARACTERISTICS OF MYOFIBER EXTERNAL LAMINA

Abstract

A variety of cytochemical methods were used to investigate the composition of mouse sarcolemma. We found that the sarcolemma is a complex composed of the myofiber cell membrane, a thin zone external to the cell membrane that contains groups that bind colloidal iron and thorium at low pH and a thicker amorphous layer that fails to stain with colloidal iron and thorium at low pH. The entire complex is periodic acid-Schiff-positive and stains with ruthenium red and strongly acid solutions of phosphotungstic acid. Although the specificity of these cytochemical stains is controversial, data obtained with them and from preliminary analyses of myofiber external lamina (EL) indicate that the myofiber cell coat is chiefly composed of glycoprotein containing a large number of carboxyl groups. The EL within the subneural apparatus of the neuromuscular junction differs from noninnervated areas in the fusion of Schwann cell and myofiber EL, the absence of collagen microfibrils, the more intense binding of divalent cations and the less intense stain with phosphotungstic acid in strongly acid solutions.