English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

In skeletal muscle, excitation leads to increased [Na(+)](i), loss of K(+), increased [K(+)](o), depolarization, and Cl(-) influx. This study quantifies these changes in rat extensor digitorum longus (EDL) muscles in vitro and in vivo using flame photometric determination of Na(+) and K(+) and (36)Cl as a tracer for Cl(-). In vitro, 5-Hz stimulation for 300 s increased intracellular Na(+) content by 4.6 ± 1.2 µmol/g wet wt (P &lt; 0.002) and decreased intracellular K(+) content by 5.5 ± 2.3 µmol/g wet wt (P &lt; 0.03). This would increase [K(+)](o) by 28 ± 12 mM, sufficient to cause severe loss of excitability as the result of inactivation of Na(+) channels. In rat EDL, in vivo stimulation at 5 Hz for 300 s or 60 Hz for 60 s induced significant loss of K(+) (P &lt; 0.01), sufficient to increase [K(+)](o) by 71 ± 22 mM and 73 ± 15 mM, respectively. In spite of this, excitability may be maintained by the rapid and marked stimulation of the electrogenic Na(+),K(+) pumps already documented. This may require full utilization of the transport capacity of Na(+),K(+) pumps, which then becomes a limiting factor for physical performance. In buffer containing (36)Cl, depolarization induced by increasing [K(+)](o) to 40-80 mM augmented intracellular (36)Cl by 120-399% (P &lt; 0.001). Stimulation for 120-300 s at 5-20 Hz increased intracellular (36)Cl by 100-188% (P &lt; 0.001). In rats, Cl(-) transport in vivo was examined by injecting (36)Cl, where electrical stimulation at 5 Hz for 300 s or 60 Hz for 60 s increased (36)Cl uptake by 81% (P &lt; 0.001) and 84% (P &lt; 0.001), respectively, indicating excitation-induced depolarization. Cl(-) influx favors repolarization, improving K(+) clearance and maintenance of excitability. In conclusion, excitation-induced fluxes of Na(+), K(+), and Cl(-) can be quantified in vivo, providing new evidence that in working muscles, extracellular accumulation of K(+) is considerably higher than previously observed and the resulting depression of membrane excitability may be a major cause of muscle fatigue.

Excitation-induced exchange of Na+, K+, and Cl− in rat EDL muscle in vitro and in vivo: Physiology and pathophysiology