Restricted diffusion of extracellular potassium at the neuromuscular junction of aged rats.

Changes in the extracellular K+ activity, aK, were recorded at the neuromuscular junction in aged and young rats. After the onset of stimulation, aK rose to a peak value which was maintained until stimulation was terminated. The peak value was greater in the older rats at any given distance. Also, it took longer for aK to attain one-half its peak value in the older animals. It is concluded that diffusion of K+ away from the end plate is probably slower in aged than in young rats.