Further Study on the Active Transport of Sodium across the Motoneuronal Membrane.

Following a previous paper tw o m ethods were em ployed in a fu rth e r investigation of the sodium pum p in ca t spinal m otoneurons: (1) to com pare th e ra te of sodium ex trusion a t different levels of th e resting po ten tia l, and (2) to depress th e sodium pum p by th e elec tro­ phoretic in jection of m etabolic inhibitors in to th e cells. The ra te of sodium extrusion was found to be independent of th e resting po ten tia l level, which suggests th a t th e diffusion channels were no t a m ain rou te for th e sodium extrusion. A successful tem porary block of the sodium pum p was m ade by th e in tracellu lar in jection of azide ions.