AJP - Gastrointestinal and Liver Physiology, Vol 255, Issue 5 647-G652, Copyright © 1988 by American Physiological Society
Functional gradients in muscle cells isolated from gallbladder, cystic duct, and common bile duct
C. Severi, J. R. Grider and G. M. Makhlouf
Department of Medicine, Medical College of Virginia, Richmond 23298-0711.
The existence of a gradient inherent to muscle cells of the biliary tract
was examined in muscle cells isolated separately from the fundus of the
gallbladder, cystic duct, and common bile duct of the dog. Muscle cells,
measured in suspension or as single perfused cells, exhibited a
proximal-to-distal gradient expressed by the magnitude of response and the
sensitivity to hormonal cholecystokinin octapeptide and neural
(acetylcholine and methionine-enkephalin) contractile agonists.
Measurements in suspensions showed that cells from the fundus 1) were 7-40
times more sensitive to contractile agonists than cells from the cystic
duct and 13-200 times more sensitive than cells from the common bile duct
and 2) generated greater maximal contraction. The latter was expressed by
the ratio of maximal responses (fundus: cystic duct cells, 1.90 +/- 0.12, P
less than 0.001; fundus: common bile duct cells, 1.50 +/- 0.07 P less than
0.001), which was independent of sensitivity to agonists. Similar results
were obtained in measurements on single cells with respect to relative
sensitivity and to ratio of maximal responses (fundus: cystic duct cells,
1.80 +/- 0.08, P less than 0.001; fundus: common bile duct cells, 1.49 +/-
0.06, P less than 0.001). The ratio of responses to low concentrations of
agonists was even higher (three- to fourfold), reflecting both the greater
sensitivity and the greater contraction of muscle cells of the fundus. We
conclude that a proximal-to-distal biliary gradient exists that is an
inherent property of muscle cells from various regions of the biliary
tract; the gradient would act to facilitate gallbladder emptying in
response to hormonal and neural stimulation.
