The frog ventricle in sucrose solution contracts for several hours at 25°C, and for as long as 24 hours at 5°G. The possibility that a fraction of the extracellular fluid remains outside of the excitable membrane was examined by measuring the efflux of tracers. The half-time for the efflux to sucrose solution at 25°C of C14 sucrose is about 1 minute, for Na24 is 6.5 minutes, and for Cl86 is 4 minutes. There is no evidence for the retention of an extracellular Na fraction. The Q10 for Na and Cl efflux is about 1.3. The half-time for K42 efflux is about 180 minutes; the Q10 is 1.7. The efflux rates of Na24, Cl36 and K42 to sucrose and to Ringer's solutions are quite similar. Ca45 efflux is only one-fifth as fast to sucrose solution as to Ringer's; the retention of Ca++ may be important for maintaining excitability in sucrose solution. P32 efflux is five times faster to sucrose solution than to Ringer's solution, and there is a similar increase in the rate of inosine loss to sucrose solution. The Q10 for efflux to sucrose solution is 2.2 for P32O4 and 2.4 for inosine. We suggest that energy metabolism is abnormal in ventricles in sucrose solution and that low temperature prolongs excitability by slowing the metabolic change.

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