A non-invasive vibrating calcium-selective electrode measures acetylcholine-induced calcium flux across the sarcolemma of a smooth muscle |
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Authors: | C. L. Devlin P. J. S. Smith |
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Affiliation: | (1) Department of Biology, Penn State University Abington, 19001 Abington, PA, USA;(2) Marine Biological Laboratory, NIH National Vibrating Probe Facility, 02543 Woods Hole, MA, USA |
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Abstract: | To determine possible sources of Ca2+ during excitation-contraction coupling in smooth muscle, a vibrating Ca2+-selective electrode was used to measure Ca2+ flux during the process of contraction. The smooth muscle model was the longitudinal muscle of the body wall of a sea cucumberSclerodactyla briareus. Because acetylcholine caused slow contractions of the muscle that were inhibited by Ca2+ channel blockers diltiazem and verapamil in earlier mechanical studies, we chose a vibrating Ca2+-selective electrode as our method to test the hypothesis that acetylcholine may be stimulating Ca2+ influx across the sarcolemma, providing a Ca2+ source during excitation-contraction coupling. Acetylcholine treatment stimulated a net Ca2+ efflux that was both dose and time dependent. We then tested two L-type Ca2+ channel blockers, diltiazem and verapamil, and two non-specific Ca2+ blockers, cobalt (Co2+) and lanthanum (La3+) on acetylcholine-induced Ca2+ flux. All four Ca2+ blockers tested potently inhibited Ca2+ efflux induced by physiological doses of acetylcholine. We propose that the acetylcholine-induced Ca2+ efflux was the result of, first, Ca2+ influx through voltage-sensitive L-type Ca2+ channels, then the rapid extrusion of Ca2+ by an outwardly directed carrier such as the Na–Ca exchanger as suggested by Li+ substitution experiments. The vibrating Ca2+ electrode has provided new insights on the active and complex role the sarcolemma plays in Ca2+ homeostasis and regulating Ca2+ redistribution during excitation-contraction coupling.Abbreviations ACh acetylcholine - E-C coupling excitation-contraction coupling - LMBW longitudinal muscle of the body wall |
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Keywords: | Ca2+ channel blockers Cobalt chloride Diltiazem Excitation-contraction coupling Lanthanum chloride Smooth muscle Verapamil Vibrating Ca2+-selective electrode |
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