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1 Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
* To whom correspondence should be addressed. E-mail: edaniel{at}ualberta.ca.
Abstract: Pacing of mouse is dependent on the spontaneous activity of interstitial cells of Cajal
in the myenteric plexus (ICC-MP). These ICC, as well as intestinal smooth muscle, contain
small membrane invaginations called caveolae. Caveolae are signaling centers formed by
insertions of caveolin proteins in the inner aspect of the plasma membrane. Caveolins bind
signaling proteins and thereby negatively modulate their signalling. We disrupted caveolae by
treating intestinal segments with methyl 
clodextrin (CD) to remove cholesterol or with water
soluble cholesterol (WSC) to load cholesterol. Both of these treatments reduced pacing
frequencies and these effects were reversed by the other agent. These treatments also inhibited
paced contractions, but complete reversal was not observed. To evaluate the specificity of the
effects of CD and WSC, additional studies were made of their effects on responses to carbamoyl
choline and to stimulation of cholinergic nerves. Neither of these treatments affected these sets
of responses compared to their respective time controls. Immunochemical and ultrastructural
studies showed that caveolin 1 was present in smooth muscle membranes and ICC-MP. CD
depleted both caveolin 1 and caveolae, while WSC increased the amount of caveolin 1
immunoreactivity and altered its distribution but failed to increase the number of caveolae. The
effects of each agent were reversed in major part by the other. We conclude that signaling
through caveolae may play a role in pacing by ICC, but does not affect responses to
acetylcholine from nerves or added exogenously.
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