Calcium requirement for axoplasmic transport in mammalian nerve

Abstract

TO account for fast axoplasmic transport, the movement of materials in nerve fibres, a model has been advanced in analogy to the sliding filament mechanism of muscle contraction¹. We have shown in in vitro studies that transport is closely dependent on oxidative metabolism and a continual supply of ATP which could be hydrolysed by the Mg²⁺–Ca²⁺ ATPase present in nerve². One might, therefore, expect a dependence of transport on either Ca²⁺ or Mg²⁺. But, in previous studies of axoplasmic transport in vitro, we and others found transport to continue as usual when nerves were placed in incubation media free of divalent cations^3–5. Some support for the involvement of Ca²⁺ in transport was provided by the fact that a block of transport was found with 50 mM oxalate, presumably by a binding of intracellular Ca²⁺ (ref. 1) and the block of organelle movement observed in single fibres exposed to 10 mM EDTA⁶. We report here that clear evidence for a participation of Ca²⁺ in axoplasmic transport was revealed when a desheathed nerve preparation was used.