Summary
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1.
The extracellular potassium concentration in the lumbar cord of low spinal cats has been measured by means of potassium sensitive microelectrodes.
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2.
There was a transient elevation of the potassium level above its resting activity (2.5–3.0 meq/l) as a result of stimulation of peripheral nerves. The amplitude of the K+-transient increased with increasing stimulus strength, stimulation in the group II and III range being particularly effective. With increasing stimulus frequency, there was a nonlinear summation of K+-transients, the amplitude corresponding to an increase of about 1–4 mM upon a train of 20 shocks (150/s).
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3.
A roughly parallel behavior of K+-transients and focal potentials was seen, indicating that the accumulation of potassium was bound mainly to the terminal areas of the nerve under stimulation. Ventral root stimulation on the other hand usually resulted in only a small increase in the potassium level.
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4.
The excitability increase of primary afferent terminals, as evoked by conditioning volleys, and the K+-transients as evoked by the same conditioning volleys often were parallel.
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5.
In contrast to their effects on the DRP, nembutal decreased and picrotoxin increased the amplitude of K+-signals. Whereas conditioning volleys in the FRA were able to block group I evoked DRPs, they were unable to block the K+-signals evoked by the same test stimulus.
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6.
The results indicate that factors other than a K+-increase are probably also involved in the process of presynaptic inhibition. An elevation in the potassium level may, however, contribute to the excitability increase in primary afferents.
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ten Bruggencate, G., Lux, H.D. & Liebl, L. Possible relationships between extracellular potassium activity and presynaptic inhibition in the spinal cord of the cat. Pflugers Arch. 349, 301–317 (1974). https://doi.org/10.1007/BF00588416
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DOI: https://doi.org/10.1007/BF00588416