Effects of lactic acid and catecholamines on contractility in fast-twitch muscles exposed to hyperkalemia. Export

@article{citeulike:615601, abstract = {Intensive exercise is associated with a pronounced increase in extracellular K+ ([K+]o). Because of the ensuing depolarization and loss of excitability, this contributes to muscle fatigue. Intensive exercise also increases the level of circulating catecholamines and lactic acid, which both have been shown to alleviate the depressing effect of hyperkalemia in slow-twitch muscles. Because of their larger exercise-induced loss of K+, fast-twitch muscles are more prone to fatigue caused by increased [K+]o than slow-twitch muscles. Fast-twitch muscles also produce more lactic acid. We therefore compared the effects of catecholamines and lactic acid on the maintenance of contractility in rat fast-twitch [extensor digitorum longus (EDL)] and slow-twitch (soleus) muscles. Intact muscles were mounted on force transducers and stimulated electrically to evoke short isometric tetani. Elevated [K+]o (11 and 13 mM) was used to reduce force to approximately 20\% of control force at 4 mM K+. In EDL, the beta2-agonist salbutamol (10(-5) M) restored tetanic force to 83 +/- 2\% of control force, whereas in soleus salbutamol restored tetanic force to 93 +/- 1\%. In both muscles, salbutamol induced hyperpolarization (5-8 mV), reduced intracellular Na+ content and increased Na+-K+ pump activity, leading to an increased K+ tolerance. Lactic acid (24 mM) restored force from 22 +/- 4\% to 58 +/- 2\% of control force in EDL, an effect that was significantly lower than in soleus muscle. These results amplify and generalize the concept that the exercise-induced acidification and increase in plasma catecholamines counterbalance fatigue arising from rundown of Na+ and K+ gradients.}, address = {Department of Physiology, University of Aarhus, Ole Worms All\'{e} 160, DK-8000 Arhus C, Denmark.}, author = {Hansen, A. K. and Clausen, T. and Nielsen, O. B.}, citeulike-article-id = {615601}, citeulike-linkout-0 = {http://dx.doi.org/10.1152/ajpcell.00600.2004}, citeulike-linkout-1 = {http://ajpcell.physiology.org/cgi/content/abstract/289/1/C104}, citeulike-linkout-2 = {http://view.ncbi.nlm.nih.gov/pubmed/15743886}, citeulike-linkout-3 = {http://www.hubmed.org/display.cgi?uids=15743886}, doi = {10.1152/ajpcell.00600.2004}, issn = {0363-6143}, journal = {Am J Physiol Cell Physiol}, keywords = {acidose, lactate}, month = {July}, number = {1}, posted-at = {2006-05-05 23:58:46}, priority = {0}, title = {Effects of lactic acid and catecholamines on contractility in fast-twitch muscles exposed to hyperkalemia.}, url = {http://dx.doi.org/10.1152/ajpcell.00600.2004}, volume = {289}, year = {2005} }

TY - JOUR ID - citeulike:615601 L3 - citeulike-article-id:615601 N2 - Intensive exercise is associated with a pronounced increase in extracellular K+ ([K+]o). Because of the ensuing depolarization and loss of excitability, this contributes to muscle fatigue. Intensive exercise also increases the level of circulating catecholamines and lactic acid, which both have been shown to alleviate the depressing effect of hyperkalemia in slow-twitch muscles. Because of their larger exercise-induced loss of K+, fast-twitch muscles are more prone to fatigue caused by increased [K+]o than slow-twitch muscles. Fast-twitch muscles also produce more lactic acid. We therefore compared the effects of catecholamines and lactic acid on the maintenance of contractility in rat fast-twitch [extensor digitorum longus (EDL)] and slow-twitch (soleus) muscles. Intact muscles were mounted on force transducers and stimulated electrically to evoke short isometric tetani. Elevated [K+]o (11 and 13 mM) was used to reduce force to approximately 20% of control force at 4 mM K+. In EDL, the beta2-agonist salbutamol (10(-5) M) restored tetanic force to 83 +/- 2% of control force, whereas in soleus salbutamol restored tetanic force to 93 +/- 1%. In both muscles, salbutamol induced hyperpolarization (5-8 mV), reduced intracellular Na+ content and increased Na+-K+ pump activity, leading to an increased K+ tolerance. Lactic acid (24 mM) restored force from 22 +/- 4% to 58 +/- 2% of control force in EDL, an effect that was significantly lower than in soleus muscle. These results amplify and generalize the concept that the exercise-induced acidification and increase in plasma catecholamines counterbalance fatigue arising from rundown of Na+ and K+ gradients. IS - 1 JF - Am J Physiol Cell Physiol SN - 0363-6143 AD - Department of Physiology, University of Aarhus, Ole Worms Allé 160, DK-8000 Arhus C, Denmark. TI - Effects of lactic acid and catecholamines on contractility in fast-twitch muscles exposed to hyperkalemia. VL - 289 KW - acidose KW - lactate AU - Hansen, AK AU - Clausen, T AU - Nielsen, OB PY - 2005/07// UR - http://dx.doi.org/10.1152/ajpcell.00600.2004 ER -