Two-dimensional coupling by gap junctions in cultured gastric smooth muscle monolayers.

We studied intercellular transfer in cultured rabbit gastric smooth muscle cell monolayers after microinjection of electrotonic current or the fluorescent probe Lucifer yellow CH. Because cultured gastric muscle cells proliferate in vitro and form regular arrays of parallel spindle-shaped cells, we sought to assess the role of cell shape and orientation in determining two-dimensional coupling properties. With the use of electron microscopy, gap junctions were identified between adjacent cells. Northern blot analyses using specific cDNA probes demonstrated expression of mRNA for the gap junction protein connexin43. Dye injection of Lucifer yellow resulted in 97% transfer to at least one adjacent cell, and 88% of adjacent cells received dye. Electrophysiological studies were performed using two intracellular microelectrodes to measure electrotonic current flow between cells at varying interelectrode distances. Current flow in the monolayers was modeled using a modified two-dimensional analysis. Initial assessment showed that the ratio of calculated space constants (longitudinal axis/perpendicular axis) was 4.4, indicating anisotropic conditions. However, when a geometric transform was used to normalize the spindle-shaped cells to regular hexagons, the space constants became statistically equivalent (200 microns longitudinal, 256 microns perpendicular). These results suggest that anisotropy of current flow in the monolayer of gastric smooth muscle cells was due primarily to the shape of the cells and not to intrinsic membrane properties or the distribution of gap junctions.