ABSTRACT
INTRODUCTION Gap junctions have been first described by electron microscopy and electrophysiology as aggregates of electrically conductive cell-to-cell channels that were permeable for ions and metabolites. During the last 15 years the subunit proteins and corresponding genes of gap junctions have been characterized, but only indirect evidence for the functional relevance of gap junction channels in mammalian cells could be obtained. The discovery of the first inherited human mutation that affected a gap junctional gene (Bergoffen et al., 1993) and, especially, the generation and characterization of mice that lack gap junctional proteins made it possible to understand the consequences of gap junctional functions in whole organisms. Thus, we are at the beginning of an exciting period when long standing hypotheses regarding gap junctional functions can be directly tested in targeted mouse mutants. Here we have attempted to summarize the present insights into the biological function of gap junctions, based mainly on investigations of connexin defective mice and humans.
