The role of na+-k+ pump and na+-channel concentrations in the
contractility of rat soleus muscle .
Harrison, A. P., O. B. Nielsen, and T. Clausen.
Department of Physiology, University of Aarhus, 8000
[angstrom]arhus C, Denmark
APStracts 3:0441R, 1996.
The dependence of contractile performance on the leak: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.
Received 9 September 1996; accepted in final form 13 December
1996.
APS Manuscript Number R547-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996