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Articles in PresS, published online ahead of print October 16, 2002
Am J Physiol Gastrointest Liver Physiol, 10.1152/ajpgi.00291.2002
Submitted on July 19, 2002
Accepted on October 3, 2002
1 Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV, USA
* To whom correspondence should be addressed. E-mail: tks{at}physio.unr.edu.
The role of the longitudinal muscle layer during the peristaltic reflex in the small and large intestine is unclear. In this study, we have made double and quadruple simultaneous intracellular recordings from longitudinal muscle (LM) and circular muscle (CM) cells of guinea-pig distal colon, to correlate the electrical activities in the two different muscle layers, during circumferential stretch. Simultaneous recordings from LM and CM cells (<200µm apart) at the oral region of colon showed that excitatory junction potentials (EJPs) discharged synchronously in both muscle layers for periods of up to 6 hours. Similarly, at the anal region of colon, inhibitory junction potentials (IJPs) discharged synchronously in the two muscle layers. Quadruple recordings from LM and CM orally at the same time as LM and CM anally, revealed that IJPs occurred synchronously in the LM and CM anally at the same time as EJPs in LM and CM located 20mm orally. Oral EJPs and anal IJPs were linearly related in amplitude between the two muscle layers. Spatio-temporal maps generated from simultaneous video imaging of the movements of the colon, combined with intracellular recordings, revealed that some LM contractions orally could be correlated in time with IJPs in CM cells anally. L-NA (100µM) abolished the IJP in LM, whereas a prominent L-NA-resistant "fast" IJP was always observed in CM. In summary, in stretched preparations, synchronized EJPs in both LM and CM orally are generated by synchronized firing of many ascending interneurons, which simultaneously activate excitatory motor neurons to both muscle layers. Similarly, synchronized IJPs in both LM and CM anally, are generated by synchronized firing of many descending interneurons, which simultaneously activate inhibitory motor neurons to both muscle layers. This synchronized motor activity ensures that both muscles around the entire circumference are excited orally at the same time as inhibited anally, thus producing net aboral propulsion.
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