A non-invasive vibrating calcium-selective electrode measures acetylcholine-induced calcium flux across the sarcolemma of a smooth muscle.
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 cucumber Sclerodactyla 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.
Devlin
C L
CL
Department of Biology, Penn State University Abington 19001, USA.
Smith
P J
PJ
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D007811:Lanthanum / Q000494:pharmacology; D008094:Lithium / Q000494:pharmacology; D008839:Microelectrodes; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism*; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism; D012616:Sea Cucumbers / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; C028521:lanthanum chloride; D003035:Cobalt; D007811:Lanthanum; D008094:Lithium; D014700:Verapamil; D004110:Diltiazem; C018021:cobaltous chloride; D000109:Acetylcholine; D002118:Calcium