Modelling action potentials and membrane currents of mammalian skeletal muscle fibres in coherence with potassium concentration changes in the T-tubular system |
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Authors: | W Wallinga S L Meijer M J Alberink M Vliek E D Wienk D L Ypey |
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Institution: | (1) Department of Signals & Systems, BME, Faculty of Electrical Engineering, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands, e-mail: w.wallinga-dejonge@el.utwente.nl, NL;(2) Leiden University Medical Centre, Department of Physiology, Leiden, The Netherlands, NL |
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Abstract: | During prolonged activity the action potentials of skeletal muscle fibres change their shape. A model study was made as to
whether potassium accumulation and removal in the tubular space is important with respect to those variations. Classical Hodgkin-Huxley
type sodium and (potassium) delayed rectifier currents were used to determine the sarcolemmal and tubular action potentials.
The resting membrane potential was described with a chloride conductance, a potassium conductance (inward rather than outward
rectifier) and a sodium conductance (minor influence) in both sarcolemmal and tubular membranes. The two potassium conductances,
the Na-K pump and the potassium diffusion between tubular compartments and to the external medium contributed to the settlement
of the potassium concentration in the tubular space. This space was divided into 20 coupled concentric compartments. In the
longitudinal direction the fibre was a cable series of 56 short segments. All the results are concerned with one of the middle
segments. During action potentials, potassium accumulates in the tubular space by outward current through both the delayed
and inward rectifier potassium conductances. In between the action potentials the potassium concentration decreases in all
compartments owing to potassium removal processes. In the outer tubular compartment the diffusion-driven potassium export
to the bathing solution is the main process. In the inner tubular compartment, potassium removal is mainly effected by re-uptake
into the sarcoplasm by means of the inward rectifier and the Na-K pump. This inward transport of potassium strongly reduces
the positive shift of the tubular resting membrane potential and the consequent decrease of the action potential amplitude
caused by inactivation of the sodium channels. Therefore, both potassium removal processes maintain excitability of the tubular
membrane in the centre of the fibre, promote excitation-contraction coupling and contribute to the prevention of fatigue.
Received: 5 May 1998 / Revised version: 27 October 1998 / Accepted: 19 January 1999 |
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Keywords: | Action potential model Inward rectifier Sodium-potassium pump Tubular potassium concentration Muscle fatigue |
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