AJP - Gastrointestinal and Liver Physiology, Vol 254, Issue 6 808-G813, Copyright © 1988 by American Physiological Society
Sources of calcium for contraction of distal circular muscle or taenia coli in the rabbit
N. Sevy and W. J. Snape Jr
Department of Medicine, Harbor-UCLA Medical Center, Torrance 90502.
Studies were performed on proximal taenia coli and distal circular muscle
from the rabbit to determine if the source of Ca2+ required for bethanechol
stimulation of contraction was similar after permeabilizing the tissues
with saponin. The EC50 for Ca2+ stimulation of contraction was pCa 6.1 +/-
0.1 for both tissues. The peak response occurred at pCa 4.5. The addition
of 1 microM calmodulin did not alter the Ca2+ EC50 or the peak response.
Caffeine (20 mM) stimulated contraction of both taenia coli and distal
circular muscle. The caffeine-stimulated contractile response was threefold
greater in the taenia than in the distal circular muscle (P less than
0.05). Perfusion of thin strips of colonic muscle with buffer, containing
10(-7) M Ca2+, reduced the amplitude of bethanechol-stimulated contraction.
The perfusion time to reduce the contraction by 50% was greater in the
proximal muscle (2.4 +/- 0.1 min) than in the distal muscle (1.1 +/- 0.5
min) (P less than 0.001). These data suggest that 1) the intracellular Ca2+
concentration necessary for contraction is similar in the proximal and
distal colon and 2) the intracellular Ca2+ stores appear to be greater in
proximal taenia coli compared with distal circular muscle.
