Heterogeneous distribution of a gap junction protein, connexin43, in the gastroduodenal junction of the guinea pig.

The gastroduodenal junction differs in morphology and function from the stomach and the duodenum. We studied the immunohistochemical distribution of the gap junction protein, connexin43, and the nerve terminal proteins, SNAP-25 and synaptotagmin, in the musculature of the guinea pig gastroduodenal junction. Connexin43-immunopositive structures were distributed throughout the circular layer of the gastroduodenal junction, most densely in the duodenal circular layer. The difference in the distribution patterns of these structures between the stomach and the duodenum was readily observed in the gastroduodenal junction. In the inner part of the circular muscle layer of the gastroduodenal junction, the connexin43-immunopositive structures were relatively few or non-existent, whereas the SNAP-25-containing nerve fibers and synaptotagmin-containing nerve terminals, clearly observed, were numerous. These findings show a heterogeneous distribution of the gap junctions and nerves in the gastroduodenal junction. The results suggest that the gastroduodenal junction has heterogeneous electrical connections among smooth muscle cells via gap junctions, and specific nerve innervation, which regulates gastroduodenal motility.