The na+ and k+ effect on the contractility of frog sartorius muscle;
implication for the mechanism of fatigue..
Bouclin, R., E. Charbonneau, and J. M. Renaud.
University of Ottawa, Department of Physiology, 451 Smyth Rd., Ottawa,
Ontario, Canada, K1H 8M5
APStracts 2:0065C, 1995.
Although a decrease in extracellular Na+ and an increase in K+ concentration
is believed to contribute to the decrease in force during fatigue, the force
of unfatigued muscle decreases only with quite large changes in Na+ and K+
concentration. The objective of this study was to determine if concomitant
and smaller changes in Na+ and K+ concentration have greater effects on
muscle contractility than individual changes. At 3 mmolelambda-1 K+, a large
decrease in Na+ from 120 to 60 mmolelambda-1 had no effect on the twitch
force, while the tetanic force decreased by 31.2%. At 120 mmole.lambda-1 Na+,
an increase in K+ from 3 to 9 mmole lambda-1 potentiated the twitch force by
41.1%, had no effect on the tetanic force at 7 mmole.lambda-1 and decreased
the tetanic force by 40.4% at 9 mmole lambda-1; both the twitch and tetanic
force was completely abolished at 11 mmole lambda-1 K+. The potentiation of
the twitch force between 3 and 9 mmole lambda-1 K+ was less at 60, 80 and 100
than at 120 mmole lambda-1 Na+. A reduction in Na+ concentration also reduced
the K+ concentration at which the twitch and tetanic force decreased and was
completely abolished. It is shown that the combined effects of Na+ and K+ on
the twitch and tetanic contraction were greater than the sum of their
individual effect. Furthermore it is proposed that neither Na+ nor K+ alone
can be considered as an important factor in the decrease in force during
fatigue, whereas together they are important for the tetanic contraction, but
not for the twitch contraction.
Received 29 August 1994; accepted in final form 3 January 1995.
APS Manuscript Number C505-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 27 February 1995.