AJP - Gastrointestinal and Liver Physiology, Vol 260, Issue 4 615-G624, Copyright © 1991 by American Physiological Society
Excitatory and inhibitory responses of Oddi's sphincter in guinea pigs
T. Hirose and Y. Ito
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
We examined the intrinsic motor innervation of the guinea pig
choledochoduodenal junction and actions of cholecystokinin octapeptide
(CCK-OP) on contractile and membrane activity of circular and longitudinal
smooth muscles from three different areas: close to the choledochal
sphincter (I); central area in the ampulla (II); and close to the duodenal
papilla (III). In response to electrical field stimulation, circular muscle
strips showed an initial twitchlike contraction followed by relaxation in
areas I and II and only a transient relaxation in the muscle strips
prepared from area III. In the longitudinal strips, the regional
differences in response to the field stimulation were not prominent, and
biphasic twitchlike contractions were observed in areas I, II, and III.
Electric field stimulation evoked excitatory junction potentials (EJPs),
inhibitory junction potentials (IJPs), or biphasic membrane response
(initial EJP followed by an IJP) in the circular and longitudinal smooth
muscle cells. Prominent regional differences were observed in areas I, II,
and III. Namely, in area III both the circular and longitudinal muscle
layers IJPs predominated, whereas in area I the response was predominantly
excitatory. CCK-OP (greater than 10-8M) evoked repetitive action potentials
in the circular muscle cells, and CCK-OP increased the frequency of slow
waves or the spontaneous action potentials in longitudinal muscle cells.
CCK-OP enhanced the amplitude of the IJPs and EJPs in both muscle layers.
It would thus appear that bile flow is controlled by complex combinations
of contraction and relaxation of the smooth muscle that may be due to
regional differences in excitatory and inhibitory innervations.
