title: Aging: stimulation rate on cardiac intracellular Na+ activity and developed tension.
abstract: Previous reports suggested that Na,K-ATPase activity and Na(+)-pump capacity decrease with senescence in left atrial myocardium of F344 rats. Current experiments were designed to determine if this reduction in the Na(+)-pump affects free intracellular Na+ levels. Mean intracellular Na+ ion activity (aiNa) was measured with Na-selective microelectrodes in left atrial muscle isolated from hearts of 4-, 14- and 25-month-old F344 rats. Preparations were stimulated randomly at frequencies between 0 and 12 h. There were no age-associated differences in aiNa measured at any frequency or in the decay of Na+ activity following discontinuation of electrical stimulation. These data indicate that the aging-related decline in Na,K-ATPase does not result in elevated aiNa even at extremely high stimulation frequencies, thus suggesting that other routes of Na+ influx and efflux are also altered in atrial muscle.
authors.affiliation: Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock 72205.
authors.forename: S
authors.initials: S
authors.lastname: Ruch
authors.forename: W B
authors.initials: WB
authors.lastname: Im
authors.forename: R H
authors.initials: RH
authors.lastname: Kennedy
authors.forename: E
authors.initials: E
authors.lastname: Seifen
authors.forename: T
authors.initials: T
authors.lastname: Akera
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism / Q000502:physiology
chemical_list: D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase