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1 Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada
* To whom correspondence should be addressed. E-mail: edaniel{at}ualberta.ca.
Pacing of mouse intestine is driven by spontaneous activity of a network of interstitial cells of Cajal (ICC-MP) in the myenteric plexus. So far, highly dissected circular muscle (CM) strips from control and mutant mice lacking ICC-MP and isolated, cultured ICC from newborn control mice were used to analyse its properties. Using intact circular and longitudinal segments of intestine, we recently reported that there were both significant similarities and differences between pacing studied in segments and from isolated, dissected tissues. Here we report additional similarities and differences in our model from those in highly reduced systems. Similar to cultured or dissected intestine, blockade of SERCA pumps with thapsigargin or CPA reduced pacing frequency, but thapsigargin was less effective than in isolated, cultured ICC. Moreover, inhibition of IP3 receptors with xestospongin C, a putative inhibitor of IP3 receptors, failed to affect pacing, but successfully blocked increased pacing frequency by phorbol ester. 2-APB, a putative blocker of IP3-mediated calcium release, caused a significant decrease in the amplitude and frequency of contractions. The mitochondrial uncoupler FCCP blocked pacing and KCl-induced contractions at a concentration of 1 µM. The cyclic nucleotide agonists SNP, forskolin and 8-bromo-cGMP inhibited pacing in CM. In LM SNP and forskolin had little effect on pacing. Furthermore, dibutyryl-cAMP did not affect pacing in CM or LM. These results suggest that pacing in intact intestine is under partly similar regulatory control as in more reduced systems. However, pacing in intact intestine is not affected by xestospongin C, which abolishes pacing in isolated, cultured ICC, and exhibits attenuated responses to thapsigargin. Also, major differences between LM and CM suggest a separate pacemaker may drive LM.
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