Unaccustomed eccentric contractions impair plasma K+ regulation in the absence of changes in muscle Na+,K+-ATPase content

Regulation of muscle potassium: exercise performance, fatigue and health implications

This review integrates from the single muscle fibre to exercising human the current understanding of the role of skeletal muscle for whole-body potassium (K⁺) regulation, and specifically the regulation of skeletal muscle [K⁺]. We describe the K⁺ transport proteins in skeletal muscle and how they contribute to, or modulate, K⁺ disturbances during exercise. Muscle and plasma K⁺ balance are markedly altered during and after high-intensity dynamic exercise (including sports), static contractions and ischaemia, which have implications for skeletal and cardiac muscle contractile performance. Moderate elevations of plasma and interstitial [K⁺] during exercise have beneficial effects on multiple physiological systems. Severe reductions of the trans-sarcolemmal K⁺ gradient likely contributes to muscle and whole-body fatigue, i.e. impaired exercise performance. Chronic or acute changes of arterial plasma [K⁺] (hyperkalaemia or hypokalaemia) have dangerous health implications for cardiac function. The current mechanisms to explain how raised extracellular [K⁺] impairs cardiac and skeletal muscle function are discussed, along with the latest cell physiology research explaining how calcium, β-adrenergic agonists, insulin or glucose act as clinical treatments for hyperkalaemia to protect the heart and skeletal muscle in vivo. Finally, whether these agents can also modulate K⁺-induced muscle fatigue are evaluated.

Effects of Futsal Demands on Serum and Salivary Levels of Trace Elements and Minerals Detected by Total Reflection X-Ray Fluorescence

The aim of this study was to monitor the circulating and salivary ion concentrations by total reflection X-ray fluorescence (TXRF) in futsal players submitted to the futsal-specific intermittent shuttle protocol (FISP). TXRF may allow identification of changes in ion concentrations induced by physical efforts. Saliva and blood samples of 13 male futsal players were collected before (Pre) and after (Post) the FISP. Salivary and plasma ion levels were detected by TXRF, and differences from Pre to Post (paired t test or Wilcoxon test) and correlations between both biological fluids were determined (P < 0.05). All saliva samples presented phosphorus (P), sulfur (S), chlorine (Cl), potassium (K), calcium (Ca), iron (Fe), zinc (Zn), bromine (Br), and rubidium (Rb). S, Cl, Ca, Fe, Cu, Zn, Br, and Rb were detected in all blood samples. K, Cu, Br, and Rb presented reduced secretion rate from Pre to Post samples (P < 0.05). The salivary concentrations of K (r = - 0.53) and Zn (r = 0.54) were correlated with plasmatic concentrations. After FISP, salivary secretion of S (r = - 0.76), Cl (r = - 0.64), P (r = - 0.67), Mn (r = - 0.74), and Zn (r = 0.69) were correlated with plasma levels. We concluded that TXRF may be used to monitor salivary (P, S, Cl, K, Ca, Fe, Zn, Br, and Rb) and circulating (S, Cl, Ca, Fe, Cu, Zn, Br, and Rb) levels of several elements in futsal athletes. However, an acute bout of futsal-specific physical effort did not significantly imbalance ion concentrations in saliva or plasma.

Leucine-Enriched Essential Amino Acids Augment Muscle Glycogen Content in Rats Seven Days after Eccentric Contraction

Eccentric contractions induce muscle damage, which impairs recovery of glycogen and adenosine tri-phosphate (ATP) content over several days. Leucine-enriched essential amino acids (LEAAs) enhance the recovery in muscles that are damaged after eccentric contractions. However, the role of LEAAs in this process remains unclear. We evaluated the content in glycogen and high energy phosphates molecules (phosphocreatine (PCr), adenosine di-phosphate (ADP) and ATP) in rats that were following electrically stimulated eccentric contractions. Muscle glycogen content decreased immediately after the contraction and remained low for the first three days after the stimulation, but increased seven days after the eccentric contraction. LEAAs administration did not change muscle glycogen content during the first three days after the contraction. Interestingly, however, it induced a further increase in muscle glycogen seven days after the stimulation. Contrarily, ATP content decreased immediately after the eccentric contraction, and remained lower for up to seven days after. Additionally, LEAAs administration did not affect the ATP content over the experimental period. Finally, ADP and PCr levels did not significantly change after the contractions or LEAA administration. LEAAs modulate the recovery of glycogen content in muscle after damage-inducing exercise.