Potassium activity, extracellular and intracellular potentials in spinal cord
Combinations of ion selective and conventional microelectrodes were used to record in the gray matter of decapitated cats' spinal cords the responses to repetitive afferent nerve stimulation. A precise correspondence was found in the spatial distribution of the amplitude of shifts of extracellular electrical potential and of elevation of K+ activity. Maximal responses to input by mixed nerves normally occurred near the base of the dorsal horn, but after the administration of convulsive doses of penicillin, the maxima moved into the ventral horn, where convulsive activity also appeared to originate. Changes of transmembrane potential of glia cells were exact replicas of responses of K+ potential recorded near such cells. The relationship of the depolarization of neuroglia to changes of extracellular K+ evoked by afferent nerve stimulation can be described by the Nernst equation (assuming constant [K+](i)). The data are compatible with the proposition that the membrane potential of glia cells is determined by extracellular K+ levels.