Abstract
The fully activated I–V relation (ĪK) for the potassium current (IK) in the Ranvier node was obtained in two ways: (a) by measuring IK values on stepping to various potentials, at the end of a depolarizing clamp pulse which fully activated IK; (b) by dividing the time dependent change in IK seen on depolarizing to a certain potential, by the time dependent change in IK seen on repolarizing from that potential to the holding potential. In solutions of high external [K+], the true ĪK curve (method a) and the current ratio ĪK curve (method b) were similar. At low external [K+], the current ratio ĪK curve was greatly distorted from the true ĪK curve. This discrepancy is attributed to K+ accumulation and depletion just outside the nodal membrane.
Using the true ĪK curves, we calculated the distortion of the current ratio ĪK curves expected on the basis of extra-cellular [K+] changes. The magnitude of diffusion barrier between the nodal membrane and the bulk solution which was necessary to give the observed distortion, is attributable to the position of the nodal membrane between the paranodal myelin.
These data support the idea that extra-cellular [K+] changes are an important determinant of the magnitude and time course of IK.
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Attwell, D., Dubois, JM. & Ojeda, C. Fully activated potassium current-voltage relationship in the Ranvier node. Pflugers Arch. 384, 49–56 (1980). https://doi.org/10.1007/BF00589513
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DOI: https://doi.org/10.1007/BF00589513