Ca2+ role in myogenic and neurogenic activities of canine ileum
circular muscle.
Cayabyab, Francisco S., Hubert Debruin, Marcel Jim[acute]enez, and
Edwin E. Daniel.
Departments of Biomedical Sciences and Electrical & Computer
Engineering, McMaster University, 1200 Main Street West, Hamilton,
Ontario L8N 3Z5; and Department of Cell Biology and Physiology,
Universitat Aut[grave]onoma de Barcelona, Bellaterra 08193 Barcelona,
Spain
APStracts 3:0132G, 1996.
Calcium's roles in myogenic and neural activation in canine ileum
circular muscle (CM) were 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. Ca2+-free Krebs abolished inhibitory junction potentials
(IJPs) and contractions prior to changes in CM membrane potentials
and while slow waves (SWs) persisted at lower amplitude and
frequency. This medium abolished SWs more rapidly in isolated CM than
in intact muscle strips and affected slow waves triggered (TSWs) by
100 msec pulses recorded near MyP or near DMP differentially in the
full-thickness preparation; TSWs did not occur in isolated CM. Ni2+,
a non-selective Ca2+ channel antagonist, left IJPs unchanged, reduced
contractions and frequencies and amplitudes of spontaneous and TSWs
but increased their durations. Nifedipine abolished contractions but
SWs, TSWs and IJPs were unaffected. Cyclopiazonic acid (CPA)
increased SW frequency, produced spikes on SW plateaus, and increased
CM tone, but did not affect IJPs or resting membrane potentials. In
nifedipine-pretreated strips, CPA decreased SW frequencies and
amplitudes, evoked less tone, depolarized membrane potentials, and
left IJPs unaltered.The neuronal N-Ca2+ channel blocker, -conotoxin
(GVIA), without affecting SWs or TSWs, abolished IJPs.Conclusion:
Ca2+ influx, not through L- or N-Ca2+ channels, helps initiate ileal
SWs; L-Ca2+ channels provide Ca2+ for contraction and N-Ca2+ channels
provide Ca2+ for IJP mediator release. Frequencies of SWs may be
modulated by uptake of Ca2+ into pacemaker stores.
Received 18 December 1995; accepted in final form 1 July 1996.
APS Manuscript Number G523-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996