Cation pumps in skeletal muscle: potential role in muscle fatigue.

Abstract

Two membrane bound pumps in skeletal muscle, the sarcolemma Na+-K+ adenosine triphosphatase (ATPase) and the sarcoplasmic reticulum Ca2+-ATPase, provide for the maintenance of transmembrane ionic gradients necessary for excitation and activation of the myofibrillar apparatus. The rate at which the pumps are capable of establishing ionic homeostasis depends on the maximal activity of the enzyme and the potential of the metabolic pathways for supplying adenosine triphosphate (ATP). The activity of the Ca2+-ATPase appears to be expressed in a fibre type specific manner with both the amount of the enzyme and the isoform type related to the speed of contraction. In contrast, only minimal differences exist between slow-twitch and fast-twitch fibres in Na+-K+ ATPase activity. Evidence is accumulating that both active transport of Na+ and K+ across the sarcolemma and Ca2+-uptake by the sarcoplasmic reticulum may be impaired in vivo in a task specific manner resulting in loss of contractile function. In contrast to the Ca2+-ATPase, the Na+-K+ ATPase can be rapidly upregulated soon after the onset of a sustained pattern of activity. Similar programmes of activity result in a downregulation of Ca2+-ATPase but at a much later time point. The manner in which the metabolic pathways reorganize following chronic activity to meet the changes in ATP demand by the cation pumps and the degree to which these adaptations are compartmentalized is uncertain.

A combination of poloxamers increases gene expression of plasmid DNA in skeletal muscle

“…35 The muscular tissues are also characterized by a high ATPase activity that is required for their normal functioning. 36 Therefore, the effect of SP1017 on DNA expression in muscles may be related to this similarity between MDR tissues and muscles. We have recently observed that SP1017 significantly increases DNA uptake into MDR cells that are normally poorly transfectable with both naked DNA and DNA complexed with cationic carriers (manuscript in preparation).…”

El acoplamiento excitación-contracción en el músculo esquelético: preguntas por responder a pesar de 50 años de estudio

“…En la fatiga se ha observado alteración de la captación máxima de Ca 2+ por el retículo sarcoplásmico (97,110,111). El trabajo reciente de Verburg y colaboradores (112), sin embargo, sugiere que no es el aumento del Ca 2+ i basal, sino el aumento localizado del Ca 2+ cerca a la tríada asociado a cada tétanos, el factor más importante para que se produzca el desacoplamiento.…”

Human neuromuscular fatigue is associated with altered Na+-K+-ATPase activity following isometric exercise

“…Accumulating evidence suggests that an impairment in excitation-contraction coupling can be a primary source of force failure with severe fatigue (49); however, other sites may contribute to varying degrees (19). More specifically, the role of the sarcolemma and t-tubular membranes in conducting repetitive action potentials has been identified as a possible contributor to fatigue in humans during voluntary exercise (20,43). Failure at the level of the sarcolemma could occur because the reduction in the transmembrane gradients for Na ϩ and K ϩ during exercise reduces the ionic membrane potential.…”