Quantification of rat cerebral cortex Na+,K(+)-ATPase: effect of age and potassium depletion.
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 x 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) mumol/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 approximately 10-fold increase within the first 4 weeks of life to reach a plateau of approximately 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.
Schmidt
T A
TA
Department of Medicine B 2142, Rigshospitalet, Copenhagen University School of Medicine, Denmark.
Larsen
J S
JS
Kjeldsen
K
K
D000375:Aging / Q000378:metabolism*; D000818:Animals; D002540:Cerebral Cortex / Q000201:enzymology* / Q000378:metabolism; D006487:Hemostasis; D008297:Male; D009132:Muscles / Q000737:chemistry / Q000378:metabolism; D010042:Ouabain / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis* / Q000378:metabolism; D014316:Tritium
D014316:Tritium; D010042:Ouabain; C045349:3-O-methyl-fluorescein phosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium