Ole Bækgaard Nielsen

Determination of cable parameters in skeletal muscle fibres during repetitive firing of action potentials

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Recent studies in rat muscle fibres indicate that repetitive firing of action potentials causes changes in fibre resting membrane conductance (Gm) that reflect regulation of ClC-1 Cl(-) and KATP K(+) ion channels. Methodologically, these findings were obtained by inserting two microelectrodes at close proximity in the same fibres enabling measurements of fibre input resistance (Rin) in between action potential trains. Since the fibre length constant (λ) could not be determined, however, the calculation of Gm relied on the assumptions that the specific cytosolic resistivity (Ri) and muscle fibre volume remained constant during the repeated action potential firing. Here we present a three-microelectrode technique that enables determinations of multiple cable parameters in action potential firing fibres including Rin and λ as well as waveform and conduction velocities of fully propagating action potentials. It is shown that in both rat and mouse EDL fibres, action potential firing leads to substantial changes in both muscle fibre volume and Ri. The analysis also showed, however, that regardless of these changes, rat and mouse EDL fibres both exhibited initial decreases in Gm that eventually was followed by a ∼3-fold, fully reversible increase in Gm after the firing of 1450-1800 action potentials. Using this three-electrode method we further show that the latter rise in Gm was closely associated with excitation failures and loss of action potential signal above -20 mV. This article is protected by copyright. All rights reserved.

Original languageEnglish
JournalThe Journal of Physiology
Pages (from-to)4417-4429
Number of pages13
Publication statusPublished - 15 Oct 2014

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