Changes of of extracellular potassium concentration induced by neuronal activity in the spinal cord of the cat

Abstract

1. Changes of extracellular K⁺ concentration, [K]_e, arising in the spinal cord of the cat in response to an afferent stimulation were studied by means of K⁺‐specific micro‐electrodes. 2. In the most active areas of the spinal cord a single volley in a large afferent input like the common peroneal nerve or the posterior tibial nerve produced a transient increase in [K]_e of 0·05–0·1 m M, which reached its peak in 0·2–0·3 sec and it declined in about 3 sec. 3. Much higher increases in [K]_e were found during repetitive stimulation of an afferent input. The highest increase (by 3 m M) was at 100 Hz, but even at 1 Hz a significant increase of 0·25 m M was observed. Equilibration of accumulated K⁺ was slow with a time constant of about 6 sec, which is much longer than could be expected for the same process in free solution. 4. A characteristic distribution of increased [K]_e was found in the spinal cord in response to 100 Hz afferent stimulation. The highest increase of 3 m M was found in and around the intermediate nucleus, but at depths between 0·9–1·8 mm the [K]_e increase exceeded 1 m M. 5. In the ventral horns afferent stimulation (100 Hz) increased [K]_e by 0·25 m M, while the same stimulation of the ventral root resulted in a [K]_e increase of less than 0·05 m M. 6. The consequences of K_e⁺ accumulation after neuronal discharge are discussed in respect to its possible role in the depolarization of primary afferent terminals.