AJP - Gastrointestinal and Liver Physiology, Vol 263, Issue 2 261-G268, Copyright © 1992 by American Physiological Society
Two-dimensional coupling by gap junctions in cultured gastric smooth muscle monolayers
D. M. Larson, R. J. Gilbert and E. C. Beyer
Mallory Institute of Pathology, Boston University School of Medicine 02118.
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.
