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.

No abstract

In the summers of 1858 and 1859, the Scot Sir James Lamont of Knockdow embarked on two cruises to Svalbard (referred to by Lamont as Spitzbergen [sic]) to hunt, make geographical surveys, and collect geological and biological specimens. Lamont's return from these voyages coincided with the publication of the joint Charles Darwin-Alfred Russel Wallace paper, ‘On the tendency of species to form varieties; on the perpetuation of varieties and species by natural means of selection’ by the Linnean Society in August 1858 and, a year later, the publication of Darwin's On the origin of species (Darwin 1958). Profoundly influenced by Darwin's ideas, Lamont initiated a correspondence with the naturalist, relating examples of what he considered to be natural selection, observed during his hunting expeditions. In his Svalbard travelogue, Seasons with the sea-horses (1861), Lamont expounded specifically upon walrus and polar bear evolution, ideas inspired by sporadic yet encouraging letters from the renowned naturalist.