Ultrastructural localization of voltage-sensitive sodium channels using [125I]alpha scorpion toxin.

The distribution of alpha scorpion toxin (alpha-ScTx) receptors was examined in differentiated mouse neuroblastoma cell cultures (N IE 115 clone) by electron microscope autoradiography using [125I]alpha-ScTx. This neurotoxin binds specifically to voltage-sensitive sodium channels, slowing down the inactivation of the sodium permeability. Quantitative analysis demonstrated that only plasma membranes were labelled. The alpha-ScTx receptors seemed to be randomly dispersed on both cell bodies and cell processes. Microvilli protruding from the cell bodies carried more sodium channels than other parts of the membrane. The specific binding site density for alpha-ScTx varied from 4 (cell body membrane) to 13 (cell process membrane) per square micrometer.