title: Unaccustomed eccentric contractions impair plasma K+ regulation in the absence of changes in muscle Na+,K+-ATPase content.
abstract: The Na+,K+-ATPase (NKA) plays a fundamental role in the regulation of skeletal muscle membrane Na+ and K+ gradients, excitability and fatigue during repeated intense contractions. Many studies have investigated the effects of acute concentric exercise on K+ regulation and skeletal muscle NKA, but almost nothing is known about the effects of repeated eccentric contractions. We therefore investigated the effects of unaccustomed maximal eccentric knee extensor contractions on K+ regulation during exercise, peak knee extensor muscle torque, and vastus lateralis muscle NKA content and 3-O-MFPase activity. Torque measurements, muscle biopsies, and venous blood samples were taken before, during and up to 7 days following the contractions in six healthy adults. Eccentric contractions reduced peak isometric muscle torque immediately post-exercise by 26±11% and serum creatine kinase concentration peaked 24 h post-exercise at 339±90 IU/L. During eccentric contractions, plasma [K+] rose during Set 1 and remained elevated at ∼4.9 mM during sets 4-10; this was despite a decline in work output by Set 4, which fell by 18.9% at set 10. The rise in plasma [K+] x work(-1) ratio was elevated over Set 2 from Set 4- Set 10. Eccentric contractions had no effect on muscle NKA content or maximal in-vitro 3-O-MFPase activity immediately post- or up to 7 d post-exercise. The sustained elevation in plasma [K+] despite a decrease in work performed by the knee extensor muscles suggests an impairment in K+ regulation during maximal eccentric contractions, possibly due to increased plasma membrane permeability or to excitation-contraction uncoupling.
authors: Institute of Sport, Exercise and Active Living (ISEAL), Muscle, Ions and Exercise Group, Victoria University, Melbourne, Victoria, Australia; Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors: Craig A
authors: CA
authors: Goodman
authors: Institute of Sport, Exercise and Active Living (ISEAL), Muscle, Ions and Exercise Group, Victoria University, Melbourne, Victoria, Australia.
authors: Jason A
authors: JA
authors: Bennie
authors: Institute of Sport, Exercise and Active Living (ISEAL), Muscle, Ions and Exercise Group, Victoria University, Melbourne, Victoria, Australia; Department of Nephrology, Royal Melbourne Hospital, Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia.
authors: Murray J
authors: MJ
authors: Leikis
authors: Institute of Sport, Exercise and Active Living (ISEAL), Muscle, Ions and Exercise Group, Victoria University, Melbourne, Victoria, Australia.
authors: Michael J
authors: MJ
authors: McKenna
mesh_terms: D000328:Adult; D015444:Exercise; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000737:chemistry*; D011188:Potassium / Q000097:blood*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium