title: Role of Na(+)-K+ pump and Na+ channel concentrations in the contractility of rat soleus muscle.
abstract: The dependence of contractile performance on the leak-to-pump ratio for Na+ has been examined. In isolated rat soleus muscle the concentration of Na(+)-K+ pumps was shown to decrease with age (-57%) or K+ deficiency (-69%), whereas Na+ channel concentration remained constant. This relative increase in the ratio between Na+ channels and Na(+)-K+ pumps was associated with a markedly faster rate of force decline (58 and 97%, respectively; both P < 0.001) during stimulation at 90 Hz and reduced subsequent force recovery (-34 and -38%, respectively; both P < 0.001). Similar effects were elicited by acute inhibition of Na(+)-K+ pump activity with ouabain. Preincubation with aconitine and veratridine, resulting in a 91 and 118% increase in Na+ influx per contraction, respectively (both P < 0.05), significantly hastened the initial rate of force decline (19%; P < 0.05 for aconitine and 69%; P < 0.001 for veratridine) and slowed recovery (-59 and -86%, respectively, both P < 0.001). It is concluded that the ratio between excitation-induced Na+ influx and Na(+)-K+ pump capacity is an important determinant for endurance and rate of recovery of force in skeletal muscle.
authors.affiliation: Department of Physiology, University of Aarhus, Denmark.
authors.forename: A P
authors.initials: AP
authors.lastname: Harrison
authors.forename: O B
authors.initials: OB
authors.lastname: Nielsen
authors.forename: T
authors.initials: T
authors.lastname: Clausen
mesh_terms: D000157:Aconitine / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D018482:Muscle, Skeletal / Q000502:physiology*; D010042:Ouabain / Q000378:metabolism; D011191:Potassium Deficiency / Q000503:physiopathology*; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D012530:Saxitoxin / Q000378:metabolism; D062687:Sodium Channel Agonists; D015222:Sodium Channels / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
chemical_list: D062687:Sodium Channel Agonists; D015222:Sodium Channels; D012530:Saxitoxin; D010042:Ouabain; D014701:Veratridine; D000254:Sodium-Potassium-Exchanging ATPase; D000157:Aconitine