Propagation speed in myelinated nerve. I. Experimental dependence on external Na and on temperature

Conduction speed (theta) in single myelinated Rana pipiens sciatic nerve fibers has been precisely measured using intracellular recording and on-line digital computer techniques. The dependence of relative speed on external Na concentration at 15 degrees C has been found to be ln(theta(1)/theta(2)) = 0.524 (+/-0.018) ln ([Na(+)](1)/[Na(+)](2)) + 0.003. Thus theta has very close to a square root dependence on [Na(+)](0) for these fibers. This experimental finding is not in complete agreement with a theoretical prediction based on a solution of the Hodgkin-Huxley (H.H.) equations. The effect of small temperature variations around 15 degrees C on theta has also been measured for Rana fibers in Ringer's solution. theta has close to an exponential dependence on T and a Q(10) of 2.95 has been estimated.