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. 1992 Sep;455:307–319. doi: 10.1113/jphysiol.1992.sp019303

Dependence of electrical slow waves of canine colonic smooth muscle on calcium gradient.

S M Ward 1, K M Sanders 1
PMCID: PMC1175646  PMID: 1282930

Abstract

1. The ionic dependence of the upstroke and plateau components of slow waves of canine colonic circular muscles was studied. 2. Reduced extracellular Ca2+ caused a decrease in the amplitude of the upstroke and plateau components, a decrease in the depolarization velocity, and a decrease in frequency. The reduction in the upstroke phase per 10-fold reduction in external Ca2+ was close to the value predicted by the Nernst relationship, suggesting that the membrane permeability to Ca2+ increases steeply during this phase. 3. Nifedipine (10(-9)-10(-6)) reduced the plateau component, but concentrations of 10(-6) M did not abolish the upstroke component. The data suggest that a nifedipine-resistant component of Ca2+ current may be involved in the upstroke. 4. Inorganic Ca2+ channel blockers (Mn2+ and Ni2+) blocked spontaneous slow waves at concentrations of 1.0 mM or less. 5. The upstroke component was more sensitive to Ni2+ than to Mn2+; a concentration of 0.040 mM-Ni2+ caused more than a 50% reduction in upstroke velocity. Ni2+ also reduced the plateau phase of slow waves. 6. The results suggest that the upstroke and plateau components of slow waves are dependent upon activation of voltage-dependent Ca2+ currents. The current responsible for the upstroke is partially resistant to dihydropyridines (at least at 10(-6) M). The current responsible for the plateau component is nifedipine-sensitive.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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