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Department of Physiology and Cell Biology, University of Nevada, Reno, Nevada 89557
The present study investigated the spatial
organization of electrical activity in the canine rectoanal region and
its relationship to motility patterns. Contraction and resting membrane
potential (Em) were measured from strips of
circular muscle isolated 0.5-8 cm from the anal verge. Rapid
frequency [25 cycles/min (cpm)] Em
oscillations (MPOs, 12 mV amplitude) were present across the thickness
of the internal anal sphincter (IAS; 0.5 cm) and
Em was constant (
52 mV). Between the IAS and
the proximal rectum an 18 mV gradient in Em
developed across the muscle thickness with the submucosal edge at
70
mV and MPOs were replaced with slow waves (20 mV amplitude, 6 cpm).
Slow waves were of greatest amplitude at the submucosal edge.
Nifedipine (1 µM) abolished MPOs but not slow waves. Contractile
frequency changes were commensurate with the changes in pacemaker
frequency. Our results suggest that changing motility patterns in the
rectoanal region are associated with differences in the characteristics
of pacemaker potentials as well as differences in the sites from which
these potentials emanate.
interstitial cells of Cajal; smooth muscle; membrane potential; internal anal sphincter; rectum
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