AJP - Gastrointestinal and Liver Physiology, Vol 243, Issue 2 134-G140, Copyright © 1982 by American Physiological Society
Effect of calcium on neurohumoral stimulation of feline colonic smooth muscle
W. J. Snape Jr
The purpose of this study was to compare the effect of altering the
extracellular calcium ion concentration on bethanechol or octapeptide of
cholecystokinin (OP-CCK) stimulation of the isolated transverse colon of
the cat. Myoelectric activity was recorded with monopolar glass-pore
electrodes. Bethanechol (10(-6) M) stimulated an increase in the number of
slow waves with superimposed spike potentials to 85.5 +/- 5.3% (P less than
0.001) compared with the basal spike activity (8.9 +/- 1.4%). OP-CCK (4 x
10(-9)) also increased spike activity (80.7 +/- 3.8%, P less than 0.001),
which was not inhibited by atropine, phentolamine, or propranolol. Addition
of 0.0 mM calcium solution to the colonic smooth muscle abolished both
slow-wave and spike activity, which returned after replacing 0.25 mM
calcium in the solution. Bethanechol stimulated a greater increase in spike
activity as the concentration of calcium was increased. OP-CCK stimulation
of colonic spike activity was more sensitive to the extracellular calcium
concentration than bethanechol stimulation. Verapamil had a minimal effect
on bethanechol stimulation of colonic spike activity, but it inhibited the
OP-CCK stimulation. These studies suggest that 1) OP-CCK appears to
stimulate colonic smooth muscle directly and 2) OP-CCK requires the
presence of a greater amount of extracellular ionic calcium in order to
stimulate colonic spike activity compared with bethanechol.
