title: Contractile activation and recovery in skinned frog muscle stimulated by ionic substitution.
abstract: Contractile activation of skinned (sarcolemma removed) skeletal muscle fibers stimulated by ionic substitution has been studied. Stimulating solutions contained varying amounts of Cl- and K+ with the [K+] x [Cl-] product kept constant at 368 mM2. Activation is a graded function of the ionic content of the stimulating solution. Mechanical threshold is reached when the [Cl-] is changed from 4 to 6.5 mM. Maximal activation occurs at 20 mM Cl-. After stimulation, fibers do not respond to a second stimulus unless allowed to recover. Contractile height reaches 50% of control levels after 30 s in the standard recovery solution (4 mM Cl). Full recovery is reached after approximately 2-4 min. The degree of contractile recovery after a constant interval (30 s) depends on the ionic composition of the recovery solution. Contractile recovery decreases 50% when the [Cl-] of the recovery solution is raised from 4 to 5.5 mM. The activation and recovery phenomena described for skinned fibers stimulated by ionic substitution are similar to those described for intact cells stimulated by elevated [K+]. This finding is consistent with the hypothesis that depolarization of resealed transverse tubules triggers release of Ca2+ from the sarcoplasmic reticulum of skinned fibers.
authors.affiliation: Department of Physiology and Biophysics, University of Illinois, Urbana 61081.
authors.forename: M D
authors.initials: MD
authors.lastname: Fill
authors.forename: P M
authors.initials: PM
authors.lastname: Best
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology*; D007474:Ion Exchange; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology*; D011894:Rana pipiens; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013268:Stimulation, Chemical; D013997:Time Factors
chemical_list: D002712:Chlorides; D011188:Potassium; D002118:Calcium