Factors Determining the Decay of K+ Potentials and Focal Potentials in the Central Nervous System

Abstract

Post-tetanic undershoots in extracellular focal potential (ΔV) and K⁺ potential (E_K) 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 ΔE_K and ΔV are recorded and they increase with the frequency and duration of stimulation. The very different time courses of undershoots of ΔV and ΔE_K indicate two hyperpolarizing influences: first, electrogenic pumping, and later, a reduced external K⁺ concentration. The importance of active K⁺ removal in determining the amplitude and duration of ΔE_K and ΔV 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.