An morphological analysis of the intestinal pacemaker cells by connexin45 knock-out mice

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By using heterozygous animals of our Cx45 knockout mice, in which Cx45 exon was replaced with Lac-Z gene as a marker, we analyzed the distribution pattern in organs and tissues of the whole body. The homozygous animals of the mutated gene die at around the embryonic day 10 because of malformation of the heart and heart failure, however, heterozygous animals are viable and fertile with normal structure. We have already reported that Cx45 was expressed in fibroblast-like cells, supposedly pacemaker cells for intestinal movements, at DMP of the small intestine. Adding to those cells, we have observed that smooth muscle cells around the pacemaker cells are expressing Cx45. Other smooth muscle cells, such as viscelral smooth muscle cells surrounding air way, urinary tract, sphincter and dilator muscle cells of the iris, ciliary body as well as vascular smooth muscle cells are also Lac-Z positive. It is important that we could detect Cx45 expressing cells that we used to be unable to identify because of their small amount of Cx45 expression. In the central nervous system, at least two types of morpholocally identified neurons were Lac-Z positive. We developed a new technique to observe three dimensional distribution pattern effectively in a thick slice. We identified 5 and 6th layers of cerebral cortex, thalamic nuclei, lateral and medial geniculate bodies, transition area of cortex to hippocampus, and habenular nuclei. Lac-Z positive neurons were distributed continuously along those nuclei. Further analysis is required for the understanding functional significance of those Cx45 expressing cells and their distribution pattern.