Differential effects of glucose and potassium lack in conduction block of myelinated and unmyelinated axons.

The effect of potassium on conduction in myelinated and unmyelinated axons lacking glucose was investigated in vitro. In the presence of ambient potassium neural excitability was lost after the same period of time in both myelinated and unmyelinated fibers. In the absence of potassium in the incubation solution however, the extinction times of the unmyelinated axons only (p less than 0.01), but not those of the myelinated ones were delayed. It is suggested that unmyelinated C fibers are more energy efficient than myelinated A axons.