Abstract
Changes in extracellular K+ levels were measured during repetitive stimulation of the excitor axon of the opener muscle of the crayfish walking leg. K+ accumulates extracellularly during axon stimulation. The extent of this accumulation is reduced by active uptake mechanisms. This accumulation probably cannot directly block action potential conduction, for neither the magnitude nor the kinetics of K+ build-up approach values shown to reduce excitability.