Juel C
Zoophysiological Laboratory B, August Krogh Institute, University of Copenhagen, Denmark.
Acta Physiol Scand. 1988 Oct;134(2):209-16. doi: 10.1111/j.1748-1716.1988.tb08481.x.
The resting membrane potential (RMP), the intracellular free Na+ concentration ([Na+]i) and the intracellular free K+ concentration ([K+]i), were measured with double-barrelled ion-selective microelectrodes in mouse soleus muscles in vitro. In addition, the Na+ contents and K+ contents have been measured with the flame photometric technique. At rest the beta 2-selective adrenoceptor agonist terbutaline (10(-5) M) increased the membrane potential and [K+]i, and decreased [Na+]i when compared with control muscles. During a 5 min stimulation period the muscles, which were incubated with the beta 2-adrenoceptor agonist, showed a smaller depolarization, a smaller decrease in [K+]i and a smaller increase in [Na+]i than stimulated control muscles. This difference was probably associated with an increased rate of Na-K-pumping in the beta 2-adrenoceptor stimulated muscles. The beta 2-agonist treated muscles were more resistant to fatigue than control muscles. This effect was significant with 10(-6) M terbutaline (25 degrees C). A depolarization obtained by increasing [K+]o was shown to reduce the maximal tension. It is postulated, that the K+ shifts, which are responsible for the depolarization during muscle activity, are one of the mechanisms underlying muscle fatigue.
采用双管离子选择性微电极在体外测定小鼠比目鱼肌的静息膜电位（RMP）、细胞内游离钠离子浓度（[Na⁺]i）和细胞内游离钾离子浓度（[K⁺]i）。此外，还用火焰光度法测定了钠离子含量和钾离子含量。静息时，与对照肌肉相比，β₂选择性肾上腺素能受体激动剂特布他林（10⁻⁵ M）可增加膜电位和[K⁺]i，并降低[Na⁺]i。在5分钟的刺激期内，与受刺激的对照肌肉相比，用β₂肾上腺素能受体激动剂孵育的肌肉去极化程度较小，[K⁺]i降低幅度较小，[Na⁺]i升高幅度较小。这种差异可能与β₂肾上腺素能受体刺激的肌肉中钠钾泵速率增加有关。用β₂激动剂处理的肌肉比对照肌肉更抗疲劳。在10⁻⁶ M特布他林（25℃）时，这种作用很显著。通过增加细胞外钾离子浓度（[K⁺]o）获得的去极化显示会降低最大张力。据推测，在肌肉活动期间负责去极化的钾离子转移是肌肉疲劳的潜在机制之一。
