Transport of Na+ inside the giant axon of squid.

The transport mechanism of Na ions within the nerve cell was studied by measuring the radioactivity distribution profile of 22Na that had been intracellularly injected into the giant axon. Specifically, we tested whether or not the movement of Na ions is coupled with the process of "fast axonal transport." Results of our measurements indicate that the intracellular transport of Na+ and the fast axonal transport are two independent processes. Very few Na ions are irreversibly sequestered into the axoplasmic vesicles involved in axonal transport. The movement of Na+ inside the axon can be modeled by a one-dimension diffusion. The effective diffusion coefficient of the intracellular Na+ was determined in this study.