Human cardiac gap junctions: isolation, ultrastructure, and protein composition.

Recent experiments from our laboratory have shown that the ultrastructure and protein composition of gap junctions isolated from rat ventricles are tissue specific, i.e., markedly different from gap junctions of liver and lens. The differences include a cytoplasmic surface component characteristic for cardiac gap junctions; this component can be visualized by two ultrastructural techniques: as a fuzzy layer in electron micrographs of thin-sectioned junctional pellets and as cytoplasmic surface particles in deep-etched freeze-fractured junctions. The component corresponds to a Mr 17,500 cytoplasmic surface domain of each of the six (Mr 47,000) rat heart gap junctional channel protein subunits that make up the gap junctional channel hexamer known as a connexon. The cytoplasmic surface component is localized at the carboxy-terminal of the subunit. Within the cytoplasmic surface component, rat cardiac gap junctions are cross-linked by disulfide linkages between subunits of the same connexon and between subunits of adjacent connexons. By contrast, the Mr 28,000 liver gap junctional subunit lacks a comparably large cytoplasmic surface component, cytoplasmic surface fuzz, cytoplasmic surface particles, and intra- and interconnexon disulfide linkages. Most of these unique characteristics of cardiac gap junctions were discovered in junctions isolated from rat ventricles. Unlike liver and lens gap junctions, cardiac gap junctions from humans, non-human primates, or other large mammals have not previously been isolated and characterized. Here we report the isolation of unproteolyzed gap junctions from the ventricle of a 24 year-old man with advanced cardiomyopathy whose heart was removed for replacement by a transplanted heart.(ABSTRACT TRUNCATED AT 250 WORDS)