Chronic Fatigue Syndrome Research Today is a free monthly online journal that collates and summarizes the latest research about Chronic Fatigue Syndrome, including details on myalgic encephalomyelitis (me), diagnosis, gradual and sudden onset. | ||||||||
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Na+-K+ pumps in the transverse-tubular system of skeletal muscle fibers preferentially use ATP from glycolysis.Dutka TL, Lamb GD Zoology, La Trobe University, Bundoora, Victoria, Australia. The Na(+)-K(+) pumps in the transverse tubular (T-) system of a muscle fiber play a vital role keeping [K(+)] in the T-system sufficiently low during activity so as to prevent chronic depolarization and consequent loss of excitability. These Na(+)-K(+) pumps are located in the triad junction, the key transduction zone controlling excitation-contraction (EC-) coupling, a region rich in glycolytic enzymes and likely having high localised ATP usage and limited substrate diffusion. This study examined whether Na(+)-K(+) pump function was dependent on ATP derived via the glycolytic pathway locally within the triad region. Single fibers from rat fast-twitch muscle were mechanically skinned, sealing off the T-system but retaining normal EC-coupling. Intracellular composition was set by the bathing solution, and action potentials (APs) triggered in the T-system, eliciting intracellular Ca(2+) release and twitch and tetanic force responses. Conditions were selected such that increased Na(+)-K(+) pump function could be detected from the consequent increase in T-system polarization and resultant faster rate of AP repriming. Na(+)-K(+) pump function was not adequately supported by maintaining cytoplasmic [ATP] at its normal resting level (~8 mM), even with 10 mM or 40 mM creatine phosphate (CP) present. Addition of as little as 1 mM of phospho(enol)pyruvate (PEP) resulted in a marked increase in Na(+)-K(+) pump function, supported by endogenous pyruvate kinase (PK) bound within the triad. These results demonstrate that the triad junction is a highly restricted micro-environment, where glycolytic re-synthesis of ATP is critical to meet high demand of the Na(+)-K(+) pump and maintain muscle excitability. Key words: Muscle fatigue, Na+/K+ -ATPase, Excitation-contraction coupling, T-system, Excitability. Published 7 June 2007 in Am J Physiol Cell Physiol.
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