Role of Na (+) -K+ pump and Na+ channel concentrations in the contractility of rat soleus muscle
Harrison, A.P.; Nielsen, O.B.; Clausen, T.
American Journal of Physiology 272(5 Pt 2): R1402-R1408
1997
ISSN/ISBN: 0002-9513 PMID: 9176330 Document Number: 474833
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 lt 0.001) during stimulation at 90 Hz and reduced subsequent force recovery (-34 and -38%, respectively; both P lt 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 lt 0.05), significantly hastened the initial rate of force decline (19%; P lt 0.05 for aconitine and 69%; P lt 0.001 for veratridine) and slowed recovery (-59 and -86%, respectively, both P lt 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.