Excitation-contraction coupling in skeletal muscle: blockade by high extracellular concentrations of calcium buffers.
High concentrations (80 to 90 millimolar) of the calcium buffers EGTA and citrate (less than 10(-7) molar free calcium ion) reversibly block excitation-contraction coupling in intact frog skeletal fibers, but do not block caffeine-induced contractures. Solutions containing the same free calcium concentration but lower concentrations of calcium buffer (1 millimolar) do not block excitation-contraction coupling. These results suggest that excitation-contraction coupling requires the presence of calcium in a "protected" extracellular compartment, probably the transverse tubular network, and that calcium is actively transported into this compartment from the muscle cell cytoplasm.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001001:Anura; D001693:Biological Transport, Active; D002118:Calcium / Q000502:physiology*; D002951:Citrates / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000502:physiology*; D011894:Rana pipiens; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D002951:Citrates; D004533:Egtazic Acid; D002118:Calcium