Properties of the Sodium Extrusion Mechanism Controlled by Nerve Growth Factor in Chick Embryo Dorsal Root Ganglionic Cells

Cell dissociates from embryonic chick dorsal root ganglia, incubated for 6 h with 22Na+, accumulated four to six times more radioactivity in the absence than in the presence of Nerve Growth Factor (NGF). The accumulation of radioactivity paralleled the external Na+ concentration, indicating that the cells may have been reaching equilibrium with the medium. Delayed presentation of NGF to 22Na+‐loaded cells caused a rapid loss of radioactivity, even with extracellular 22Na+ still present, demonstrating that NGF caused an overall efflux of Na+ rather than an accelerated equilibration. The Na+ exclusion from 22Na+‐loaded cells was dependent upon NGF concentration. Use of nutrient‐rich medium, serum, and certain hormones and other proteins did not prevent the Na+ accumulation in the absence of NGF or its reversion by delayed NGF administration. Incubation of the ganglionic cells with ouabain or dinitrophenol during the 22Na+ loading period (no NGF) increased the rate, but not the magnitude, of loading. The same incubation carried out in a Na+‐free medium and followed by 22Na+ presentation resulted in fast radioactive loading that was identical to that occurring in drug‐free, NGF‐deprived cells and was not prevented by presentation of NGF together with the 22Na+. These data are consistent with a model in which NGF acts through a Na+ pump rather than by restricting Na+ influxes.