Can. J. Physiol. Pharmacol. 1975.53:923-934. Downloaded from www.nrcresearchpress.com by Calif Dig Lib - Davis on 01/03/15. For personal use only.

Factors Determining the Decay of K' Potentials and Focal Potentials in the Central Nervous System Dcpurtnzent ofResearch in Anaesthesia, McGill University, Morztreal, Q~4ebt.c.F13G I Y6 Received May 13, 1975

K R N J E V IK., ~ , and MORRIS.M. E. 1975. Factors determining the decay of K+ potentials and focal potentials in the central nervous system. Can. J . Physiol. Pharmacol. 53.923-934. Post-tetanic undershoots in extracellular focal potential (AV) and K+ potential (EK)can be recorded in the cuneate nucleus and dorsal horn of Dial-anaesthetized or decerebrate cat. They are seen best at depths where the largest AEK and AV are recorded and they increase with the frequency and duration of stimulation. The very different time courses of undershoots of A V and AEK indicate two hyperpolarizing influences: first. electrogenic pumping, and later, a reduced external K+ concentration. The importance of active Kt removal in determining the amplitude and duration of AEKand AV is illustrated by their marked potentiation (as well as the disappearance of post-tetanic undershoots) induced by a lowering of blood pressure or local application of strophanthidin.

K K N J E VK. ~ ~et , MORRIS.M. E. 1975. Factors determining the decay c~fK+ potentials and focal potentials in the central nervous system. Can. J. Physiol. Pharmacol. 53,923-934. Chez le chat decerebre ou anesthesie au Dial, on enregistre dans le noyau de Burdach et les cornes dorsales unrebond post-tetanique positif du potentiel local (AV)et negatif dupotentiel de K+ ( E K ) .Ces rebonds atteignent un maximum a la profondeur ou I'on enregistre les plus fortes hatnsses de AEKet AV pendant la stimulation, et ils augmentent avec la frequence et la duree du tetanos. Deux influences hyperpolarisantes distinctes sont indiquees par les differentes latences des rebonds de AV et ~ E Kd'abord, : un effet electrogene de la pompe Na-K, et ensuite une baisse a reabsorption active du K' sur du niveau de K+ extracellulaire. L'influence dkterminante de B I'amplittlde et la duree de AEK et AV est bien demontree par leur forte augmentation ainsi que la disparition des rebonds post-tetaniques qui ensuite une chute de la tension arterielle ou l'application locale de la strophanthidine.

IntroducQion In an accompanying paper, we have emphasized the markcd general correspondcnce between negative slow potentials recorded extraeellularly near primary afferent terminals during repetitive activity, particularly in the cuneate nucleus, and the extracellular accumulation of K + observed simultaneously at the same site (Krnjevie and Morris 1 9 7 5 ~ ) .Such good agreement made it likely that the focal potentials were caused by the depolarizing effect of K + . Howevcr, thcrc was a consistent discrepancy between the rates of dccay of the K" potential change ( A E ~ ~and ) the focal potential change ( A V ) , the latter being usually much more rapid and followed by a clear undershoot, which is not shown so regularly by LIE,

Factors determining the decay of K+ potentials and focal potentials in the central nervous system.

Post-tetanic undershoots in extracellular focal potential (deltaV) and K+ potential (EK) can be recorded in the cuneate nucleus and dorsal horn of Dia...
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