Dissociation of action potentials from contraction in single crab muscle fibers.
In single crab fibers (Callinectes danae) bathed in Ca2+-free media, Ba2+ action potentials did not elicit tension. In contrast, Sr2+ spikes evoked twitches similar in amplitude to those accompanying the control Ca2+ spikes. Tension development in these fibers, therefore, depends on the ionic species carrying the inward current during membrane excitation. The Ca2" or Sr2+ influx appears insufficient to evoke the observed twitch tensions, and it seems necessary to postulate mobilization of an intracellular source of Ca1+. Procaine, which suppresses release of Ca2+ from sarcoplasmic reticulum, depressed twitch tension but did not reduce the overshoot or duration of Ca2+ or Sr2+ spikes. This finding is compatible with the suggestion that the contractions results from release of Ca2+ from the sarcoplasmic reticulum initiated by signals given by the influx of Ca2+ or Sr2+, but not Ba2+.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001464:Barium / Q000494:pharmacology; D003386:Brachyura; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D005071:Evoked Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D011343:Procaine / Q000494:pharmacology; D013324:Strontium / Q000494:pharmacology
D001464:Barium; D011343:Procaine; D002118:Calcium; D013324:Strontium