Role of low and high-voltage activated Ca2+-dependent K+ currents in the control of alpha-motoneuron discharge and its implication in hyperreflexia

Sharmila Venugopal,Ranu Jung,Thomas M Hamm

doi:10.1186/1471-2202-11-s1-p158

Sharmila Venugopal, Ranu Jung + Show 1 more

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https://doi.org/10.1186/1471-2202-11-s1-p158

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Abstract

Specificity of calcium-activated potassium (K+) currents to different sources of calcium has been noted in many neurons (e.g.1). Recently, in spinal alpha-motoneurons (α-MN), it was shown that the low-voltage activated L-type calcium currents (also known as persistent calcium currents) activate an exclusive subset of small conductance K+ currents (SKL)2. The SKL currents were distinct from the medium after-hyperpolarization (mAHP) producing N/P-type calcium activated K+ currents (SKAHP currents). The same study further suggested that an enhancement of persistent calcium current often observed after chronic spinalization can in part be due to reduced availability of the SKL channels albeit mAHP remained unchanged. While mAHP has been suggested to be integral in controlling motoneuron firing frequencies and grading L-Ca activation, the role of SKL currents in motoneuron discharge is unknown. The goal of this study is to characterize the influence of SKAHP and SKL currents on motoneuron firing frequencies. Here we test the hypothesis that SKAHP and SKL currents play differential roles in the control of persistent inward currents that are key determinants of motoneuron excitability.

Highlights

Specificity of calcium-activated potassium (K+) currents to different sources of calcium has been noted in many neurons (e.g.1)
The model a-MN shows counter-clockwise hysteresis in the injected current-frequency (I-f) relationship (Fig. 1, control) as observed in many chronic spinal sacrocaudal motoneurons. This hysteresis is mediated by the dendritic L-Ca and persistent sodium currents
A selective blockade of somatic SKAHP greatly increases the spike frequencies consistent with experimental findings that medium after-hyperpolarization (mAHP) is integral for controlling a-MN frequencies

Summary

Introduction

Specificity of calcium-activated potassium (K+) currents to different sources of calcium has been noted in many neurons (e.g.1). Currents are confined to the soma along with action potential causing fast sodium and delayed rectifier K+ currents. Model simulations are performed using the XPPAUT software.

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