Gap junctions: New tools, new answers, new questions

The big news is that gap junctions of different kinds are formed by a number of homologous proteins termed connexins, which are encoded by a gene family. Specific connexins are expressed in more than one tissue, and a single cell type may express more than one connexin. Differences between gap junctions can result from differences between the connexin or connexins forming them, as well as from differences between the cells expressing a given connexin. Specific antibodies and nucleotide probes for the connexins are allowing study of distribution, function, and differential regulation of their expression. Moreover, their conductance can now be studied at the single-channel level. Finally, exogenous expression systems permit analysis in controlled environments and with specifically modified cDNAs and cRNAs.