Bouclin R, Charbonneau E, Renaud J M
Department of Physiology, University of Ottawa, Ontario, Canada.
Am J Physiol. 1995 Jun;268(6 Pt 1):C1528-36. doi: 10.1152/ajpcell.1995.268.6.C1528.
Although a decrease in extracellular Na+ and an increase in K+ concentration are 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 whether concomitant and smaller changes in Na+ and K+ concentration have greater effects on muscle contractility than individual changes. At 3 mM K+, a large decrease in Na+ from 120 to 60 mM had no effect on the twitch force, while the tetanic force decreased by 31.2%. At 120 mM Na+, an increase in K+ from 3 to 9 mM potentiated the twitch force by 41.1%, had no effect on the tetanic force at 7 mM, and decreased the tetanic force by 40.4% at 9 mM; both the twitch force and tetanic force were completely abolished at 11 mM K+. The potentiation of the twitch force between 3 and 9 mM K+ was less at 60, 80, and 100 mM than at 120 mM Na+. A reduction in Na+ concentration also reduced the K+ concentration at which the twitch force and tetanic force decreased and were completely abolished. It is shown that the combined effects of Na+ and K+ on the twitch and tetanic contractions were greater than the sum of their individual effects. 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.
尽管细胞外钠离子减少和钾离子浓度增加被认为是疲劳期间力量下降的原因，但未疲劳肌肉的力量仅在钠离子和钾离子浓度发生相当大的变化时才会下降。本研究的目的是确定钠离子和钾离子浓度同时发生的较小变化是否比单独变化对肌肉收缩力有更大影响。在钾离子浓度为3 mM时，钠离子浓度从120 mM大幅降至60 mM对单收缩力没有影响，而强直收缩力下降了31.2%。在钠离子浓度为120 mM时，钾离子浓度从3 mM增加到9 mM使单收缩力增强了41.1%，在钾离子浓度为7 mM时对强直收缩力没有影响，而在钾离子浓度为9 mM时使强直收缩力下降了40.4%；在钾离子浓度为11 mM时，单收缩力和强直收缩力均完全消失。在钠离子浓度为60、80和100 mM时，钾离子浓度在3至9 mM之间单收缩力的增强幅度小于在钠离子浓度为120 mM时。钠离子浓度降低也降低了单收缩力和强直收缩力下降及完全消失时的钾离子浓度。结果表明，钠离子和钾离子对单收缩和强直收缩的联合作用大于它们各自作用的总和。此外，有人提出，钠离子和钾离子单独都不能被视为疲劳期间力量下降的重要因素，而它们共同作用对强直收缩很重要，但对单收缩不重要。
