期刊
AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY
卷 317, 期 5, 页码 C900-C909出版社
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/ajpcell.00104.2019
关键词
elevated extracellular potassium; force and power potentiation; free cytosolic calcium concentration; subtetanic stimulation frequency
资金
- Danish Council for Independent Research
- Augustinus Foundation
- A.P. Moller Foundation
- Torben and Alice Frimodts Foundation
- Lundbeck Foundation
- Christian and Ottilia Brorsons Travel Grant
- Swedish Research Council [K2014-52X-10842-21-5]
- Swedish Research Council for Sport Science [P2014-0037, P2018-0137]
- Carl and Ellen Hertz's Grant
The extracellular K+ concentration ([K+](o)) increases during physical exercise. We here studied whether moderately elevated [K+] o may increase force and power output during contractions at in vivo-like subtetanic frequencies and whether such potentiation was associated with increased cytosolic free Ca2+ concentration ([Ca2+](i)) during contractions. Isolated whole soleus and extensor digitorum longus (EDL) rat muscles were incubated at different levels of [K+](o), and isometric and dynamic contractility were tested at various stimulation frequencies. Furthermore, [Ca2+](i) at rest and during contraction was measured along with isometric force in single mouse flexor digitorum brevis (FDB) fibers exposed to elevated [K+](o). Elevating [K+](o) from 4 mM up to 8 mM (soleus) and 11 mM (EDL) increased isometric force at subtetanic frequencies, 2-15 Hz in soleus and up to 50 Hz in EDL, while inhibition was seen at tetanic frequency in both muscle types. Elevating [K+](o) also increased peak power of dynamic subtetanic contractions, with potentiation being more pronounced in EDL than in soleus muscles. The force-potentiating effect of elevated [K+](o) was transient in FDB single fibers, reaching peak after similar to 4 and 2.5 min in 9 and 11 mM [K+](o), respectively. At the time of peak potentiation, force and [Ca2+](i) during 15-Hz contractions were significantly increased, whereas force was slightly decreased and [Ca2+](i) unchanged during 50-Hz contractions. Moderate elevation of [K+](o) can transiently potentiate force and power during contractions at subtetanic frequencies, which can be explained by a higher [Ca2+](i) during contractions.
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