Skeletal muscle Na,K-pump concentration in children and its relationship to cardiac glycoside distribution

Skeletal muscle Na,K-pump (cardiac glycoside receptor) concentration was quantified in 18 O- to 8-year-old human subjects by vanadate faciliated [³H]ouabain binding to intact vastus lateralis samples obtained at autopsy. No age-dependent change in [³H]ouabain binding site concentration was observed. Mean value ± S.E.M. was 268 ± 17 pmol/g wet wt. (n = 18), range 182 to 433 pmol/g wet wt. At the age of 1 day, 3.5 month and 8 years and 8 months, unspecific uptake and retention of [³H]ouabain was 1.6, 1.4 and 1.5% of the total uptake and retention; release of specifically bound [³H]ouabain during the washout procedure took place with T( 1/2 ) of 97, 90 and 73 hr; and apparent affinity constants for [³H]ouabain binding (K(D)) was 1.3 x 10^-8, 0.9 x 10^-8 and 1.2 x 10^-8 mol/l. [³H]Ouabain binding site concentrations and kinetics were in agreement with values from adults except that in children apparent affinity constant (K(D)) was 1.7 times the value in adults. The observation of no age-dependent changes in human skeletal musle Na,K-adenosine triphosphatase concentration was at variance with the observations of such changes in animals. The total number of Na,K-pumps in the pool of skeletal muscles increased from 10 to 50 times that in the heart from birth to old age. The skeletal muscle pool of Na,K-pumps seems to constitute a distribution volume of importance during digitalization in children as well as adults. The larger distribution volume for cardiac glycosides in children as compared to adults did not seem to be due to a relatively larger binding of cardiac glycosides to the Na,K-pump in skeletal muscles in young age.