Excitation-contraction coupling in skeletal muscle: blockade by high extracellular concentrations of calcium buffers

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Science  16 Jun 1978:
Vol. 200, Issue 4347, pp. 1270-1272
DOI: 10.1126/science.96524


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.