Submitted on May 31, 2005
Accepted on November 21, 2005
Aging augments interstitial K+ concentrations in active muscle of rats
Jianhua Li1, Lawrence I. Sinoway2, and Yuk-Chow Ng3*
1 Division of Cardiology, The Pennsylvania State University, College Of Medicine, Hershey, PA, USA
2 Division of Cardiology, The Pennsylvania State University, College Of Medicine, Hershey, PA, USA; Lebanon VA Medical Center, Lebanon, PA, USA
3 Department of Pharmacology, The Pennsylvania State University, College of Medicine, Hershey, PA, USA
* To whom correspondence should be addressed. E-mail: ycn1{at}psu.edu.
Skeletal muscle performance declines with advancing age and the underlying mechanism is not completely understood. A large body of convincing evidence has demonstrated a crucial role for interstitial K+ ([K+]o) in modulating contractile function of skeletal muscle. The present study tested the hypothesis that during muscle contraction there is a greater accumulation of [K+]o in aged compared to adult skeletal muscle. Twitch muscle contraction was induced by electrical stimulation of the sciatic nerves of 8- and 32-month old Fischer 344 x Brown Norway rats. Levels of [K+]o were measured continuously by a microdialysis technique with the probes inserted into the gastrocnemius muscle. Stimulation at 1, 3, and 5 Hz elevated muscle [K+]o by 52%, 64%, and 88% in adult rats, and by 78%, 98%, and 104% in aged rats, respectively, and the increase was significantly higher in aged than in adult rats. Recovery for [K+]o, as measured by the time for [K+]o to recover by 20% (T20) and 50% (T50) from peak response after stimulation, was slower in aged rats. Ouabain (5 mM), a specific inhibitor of the Na-K pump, was added in the perfusate to inhibit the re-uptake of K+ into the cells in order to assess the role of the pump in the overall K+-balance. Ouabain elevated muscle [K+]o at rest, and the effect was significantly attenuated in aged animals. The present data demonstrated an augmented [K+]o in aged skeletal muscle compared to adult skeletal muscle, and suggested that an alteration in the function of the Na-K pump may contribute, in part, to the deficiency in K+-balance in skeletal muscle of aged rats.
