Freeze-fracture studies of nexuses between smooth muscle cells. Close relationship to sarcoplasmic reticulum.

Abstract

The freeze-fracture appearance of the nexus was compared in the smooth muscle of guinea pig sphincter pupillae, portal vein, pulmonary artery, taenia coli, ureter and vas deferens, mouse vas deferens, chicken gizzard and anterior mesenteric artery and toad stomach. Nexuses are particularly numerous in the guinea pig sphincter pupillae; they are usually oval and their average area is 0.15 .mu.m2, although some were as large as 0.6 .mu.m2. Small aggregations of particles were observed which were not recognizable as nexuses in thin section. The minimum size of a nexus is discussed. The number of nexuses per cell in this preparation is of the order of tens rather than hundreds. All nexuses examined had 6-9 nm particles in the PF face [cytoplasm behind], with corresponding 3-4-nm pits on the EF face [extracellular space behind] forming a polygonal, tending towards a hexagonal, lattice. The nexuses are arranged in rows parallel to the main axis of the cell, usually alternating with longitudinal rows of plasmalemmal vesicles. Many nexuses in the guinea pig sphincter pupillae, chicken gizzard, and toad stomach show a close relationship with sarcoplasmic reticulum. This relationship may have some role in current flow across the specialized junction.