Quantification of Rat Cerebral Cortex Na+,K+‐ATPase: Effect of Age and Potassium Depletion

Thomas Andersen Schmidt, Jim Stenfatt Larsen, Keld Kjeldsen

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    Abstrakt

    Abstract: Na+,K+‐ATPase concentration in rat cerebral cortex was studied by vanadate‐facilitated [3H]ouabain binding to intact samples and by K+‐dependent 3‐O‐methylfluorescein phosphatase activity determinations in crude homogenates. Methodological errors of both methods were evaluated. [3H]Ouabain binding to cerebral cortex obtained from 12‐week‐old rats measured incubating samples in buffer containing [3H]ouabain, and ouabain at a final concentration of 1 × 10–6 mol/L gave a value of 11,351 ± 177 (n = 5) pmol/g wet weight (mean ± SEM) without any significant variation between the lobes. Evaluation of affinity for ouabain was in agreement with a heterogeneous population of [3H]ouabain binding sites. K+‐dependent 3‐O‐methylfluorescein phosphatase activity in crude cerebral homogenates of age‐matched rats was 7.24 ± 0.14 (n = 5) μmol/min/g wet weight, corresponding to a Na+,K+‐ATPase concentration of 12,209 ± 236 pmol/g wet weight. It was concluded that the present methods were suitable for quantitative studies of cerebral cortex Na+,K+‐ATPase. The concentration of rat cerebral cortex Na+,K+‐ATPase showed ∼10‐fold increase within the first 4 weeks of life to reach a plateau of ∼11,000–12,000 pmol/g wet weight, indicating a larger synthesis of Na+,K+ pumps than tissue mass in rat cerebral cortex during the first 4 weeks of development. K+ depletion induced by K+‐deficient fodder for 2 weeks resulted in a slight tendency toward a reduction in K+ content (6%, p > 0.5) and Na+,K+‐ATPase concentration (3%, p > 0.4) in cerebral cortex, whereas soleus muscle K+ content and Na+,K+‐ATPase concentration were decreased by 30 (p < 0.02) and 32% (p < 0.001), respectively. Hence, during K+ depletion, cerebral cortex can maintain almost normal K+ homeostasis, whereas K+ as well as Na+,K+ pumps are lost from skeletal muscles.

    OriginalsprogEngelsk
    Sider (fra-til)2094-2104
    Antal sider11
    TidsskriftJournal of Neurochemistry
    Vol/bind59
    Udgave nummer6
    DOI
    StatusUdgivet - dec. 1992

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