The aim of this study was to determine if the structural integrity of a region in the cytoplasmic loop (amino acids 119–144; region “L2”) of connexin43 (Cx43) is necessary to maintain normal channel function.

Cx43 is the most abundant gap junction protein in the heart. The ability of these channels to close under pathologic conditions such as ischemia may be a key substrate for cardiac arrhythmias. Previous studies have shown that Cx43 regulation involves the intramolecular interaction of its carboxyl terminal domain (a “gating particle”) with a separate region of the molecule acting as a receptor. We recently proposed that a region in the cytoplasmic loop of Cx43 (amino acids 119–144; region “L2”) might function as a receptor.

Using site-directed mutagenesis and patch clamp analysis, as well as fluorescent microscopy, we examined gap junction plaque formation and channel properties of Cx43 L2 mutants.

Deletions of 5 to 6 amino acids within the L2 domain interfered with the formation of functional gap junction channels, although gap junction plaques were clearly visible. Selected point mutations in the region (including those present in patients with oculodentodigital dysplasia) caused modifications ranging from complete channel closure to changes in unitary conductance.

These results show that the L2 region is essential for maintenance of the normal architecture of the channel pore. This information is consistent with the notion that the L2 region could be a receptor for the carboxy terminal domain; the latter interaction would lead to channel closure under conditions such as myocardial ischemia and infarction.