Comparisons of neural and pacing activities in intestinal segments from W/W++ and W/W(V) mice.

We studied pacing and neurotransmission in longitudinal (LM) and circular muscle (CM) in intestine of W/W++ and W/W(V) mice. Electrical field-stimulation (EFS) of nerves in LM segments was more inhibitory in W/W(V) mice than in W/W++ mice. No inhibitory input to CM segments of W/W(V) mice was found. The EFS, after nerve block, entrained segments of both W/W++ and mutant mice with 10 ms pulses, and entrained those of mutant mice more readily at 1 and 3 ms pulses. Pacing with external electrodes did not depend on interstitial cells of Cajal in the myenteric plexus (ICC-MP). 2-Aminoethoxydiphenyl borate (2-APB), putative antagonist at IP3 receptors, store-operated channels and the Sacro-endoplasmic reticulum Ca2+ ATPase pump, reduced frequency and amplitudes of pacing of LM segments from W/W(V) mice as it did in BALB/c mice. Thus, its actions may not require ICC-MP. SKF 96365, a putative inhibitor of store-operated channels, reduced frequencies and amplitudes of intestinal segments in W/W++ mice at 10 or 30 micromol L-1. This resulted from blocking L-Ca2+-channels. Thus, no evidence was found that store-operated channels play a role in pacing. In LM segments of W/W(V), SKF 96365 had no effects on frequency of contractions. We conclude, results from models of severely reduced systems may not be applicable to intact ICC networks.