Rapid loss of the twitch of frog's skeletal muscle fibers in OCa ++ bicarbonate-buffered ringer's solution

Abstract

In experiments using preparations containing 1, 2, or 3 twitch fibers dissected from the semitendinosus muscle, the twitch was eliminated or greatly reduced (i.e., <10% of control) when the preparations were exposed for < 10 min to a OCa ++, bicarbonate-buffered Ringer's solution (37 out of 41 experiments). Replacing the bicarbonate buffer by a tris buffer delayed the loss of the twitch in OCa ++ solutions. An even greater delay was produced by substituting a phosphate buffer for the bicarbonate. In 7 out of 12 experiments, twitches of control size or larger continued for 8 to 18 min in a OCa ++, phosphate-buffered solution; in the other 5 experiments the twitch was reduced or eliminated < 8 min. The loss of the twitch takes much longer than required for removal of extracellular Ca ++ ions from the t-tubules and much shorter than required for reduction of the sarcoplasmic reticular stores of Ca ++. The results support the ‘trigger Ca ++’ hypothesis which proposes that t-tubular membrane-bound Ca ++ ions play an essential role in excitation-contraction coupling.