AJP - Gastrointestinal and Liver Physiology, Vol 260, Issue 3 390-G398, Copyright © 1991 by American Physiological Society
Correlation between electrical and morphological properties of canine pyloric circular muscle
F. Vogalis, S. M. Ward and K. M. Sanders
Department of Physiology, University of Nevada, School of Medicine, Reno 89557.
Electrical slow waves decay in amplitude as they conduct from the myenteric
to the submucosal regions of the circular muscle layer in the canine
pyloric sphincter. We used the partitioned chamber method to study the
passive and active properties of pyloric muscles, and we found that length
constants of circular muscles of myenteric region were significantly longer
than muscles near the submucosal surface. These data suggested differences
in either membrane resistance, junctional resistance, or cytoplasmic
resistance. The first parameter was evaluated by measuring time constants
in intact tissues and single cells isolated from the submucosal and
myenteric regions. Membrane time constants were not different in the two
regions, nor were differences found in the input resistances of isolated
cells. Morphological studies failed to demonstrate differences in cell
diameters in the two regions suggesting that cytoplasmic resistances are
similar. These findings suggest that the different cable properties in the
two regions may be due to differences in electrical coupling. Morphological
examination revealed similar numbers of gap junctions between cells in the
two regions, but large differences were noted in the size of muscular
bundles. Muscles of the myenteric region were arranged into large, tightly
packed bundles, whereas muscles of the submucosal region consisted of small
bundles with an extensive extracellular space filled with connective
tissue. We suggest that the difference in cable properties may be due to
differences in electrical coupling between bundles. These data suggest that
submucosal muscles function more like a multiunit smooth muscle, whereas
myenteric muscles behave as a single unit.
