Ca2+ role in myogenic and neurogenic activities of canine ileum circular muscle
Cayabyab, F.S.; deBruin, H.; Jiménez, M.; Daniel, E.E.
American Journal of Physiology 271(6 Pt 1): G1053-G1066
1996
ISSN/ISBN: 0002-9513 PMID: 8997250 Document Number: 466230
The role of Ca-2+ in myogenic and neural activation in canine ileum circular muscle (CM) was studied during simultaneous recordings of contractile and electrical activity in cross-sectioned slabs of muscularis externa or of isolated CM with deep muscular plexus (DMP) intact. Ca-2+-free Krebs solution abolished inhibitory junction potentials (IJP) and contractions before changes in CM membrane potentials and while slow waves (SW) persisted at lower amplitude and frequency. This medium abolished SW more rapidly in isolated CM than in intact muscle strips and affected triggered SW (TSW) by 100-ms pulses recorded near myenteric plexus or near DMP differentially in the full-thickness preparation; TSW did not occur in isolated CM. Ni-2+, a nonselective Ca-2+ channel antagonist, left IJP unchanged and reduced contractions, frequencies, and amplitudes of spontaneous SW and TSW, but increased their durations. Nifedipine abolished contractions but SW, TSW, and IJP were unaffected. Cyclopiazonic acid (CPA) increased SW frequency, produced spikes on SW plateaus, and increased CM tone, but did not affect IJP or resting membrane potentials. In nifedipine-pretreated strips, CPA decreased SW frequencies and amplitudes, evoked less tone, depolarized membrane potentials, and left IJP unaltered. The neuronal N-type Ca-2+, channel blocker omega-conotoxin GVIA abolished IJP, without affecting SW or TSW We conclude that Ca-2+ influx, not through L- or N-type Ca-2+ channels, helps initiate ileal SW; L-type Ca-2+ channels provide Ca-2+ for contraction and N-type Ca-2+ channels provide Ca-2+ for IJP mediator release. Frequencies of SW may be modulated by uptake of Ca-2+ into pacemaker stores.