Release of Calcium-45 from Frog Nerves during Electrical Activity

Abstract

Shanes and Bianchi¹ have demonstrated that stimulation of frog sartorius muscle accelerates the release of calcium-45 loaded on muscles, although Harris² had failed to observe this effect. Koketsu and Miyamoto³ recently confirmed an increase in the output of calcium-45 during muscle activity. An important problem remains, however, whether acceleration of calcium output during activity is caused by the mechanism specific of the contractile system or actually is responsible for the electrical membrane phenomena. Hodgkin and Keynes⁴ have reported that no change in calcium efflux can be detected during stimulation of squid axon, concluding that calcium movement during nervous activity is wholly inward. Furthermore, the 30-fold greater influx of calcium per impulse in muscle than in nerve despite the near equality of the resting influxes has been noted as consistent with a special role for calcium in contraction⁵.