title: Aging augments interstitial K+ concentrations in active muscle of rats.
abstract: 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+ concentration ([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 with adult skeletal muscle. Twitch muscle contraction was induced by electrical stimulation of the sciatic nerves of 8- and 32-mo-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 and 50% 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 reuptake of K+ into the cells 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 with adult skeletal muscle, and the data 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.
authors.affiliation: Division of Cardiology, Pennsylvania State College of Medicine, Milton S. Hershey Medical Center, 500 University Dr., Hershey, PA 17033, USA.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Li
authors.forename: Lawrence I
authors.initials: LI
authors.lastname: Sinoway
authors.forename: Yuk-Chow
authors.initials: YC
authors.lastname: Ng
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D012584:Sciatic Nerve; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium