Summary
The effect of hypoxia on K+ uptake activity in cultured rat brain capillary endothelial cells (RBEC) was investigated by using 86Rb+ as a tracer for K+ Exposure of RBEC to hypoxia (95% N2/5% CO2, 24 hr) reduced Na+,K+-ATPase activity by 39%, whereas it significantly increased Na+-K+-Cl- cotransport activity by 48%. Exposure of RBEC to oligomycin, a metabolic inhibitor, led to a complete inhibition of Na+,K+-ATPase and a coordinated increase of Na+-K+-Cl- cotransport activity up to 2-fold. Oligomycin also increased the rate of K+ efflux. The reduction of oligomycin-augmented Na+-K+-Cl- cotransport activity by protein-tyrosine kinase inhibitors (genistein, 50 µM; herbimycin A, 10 µM) and the ineffectiveness of inhibitors of either protein kinase C (bisindolylmaleimide, 500 nM) or protein kinase A (H8, 20 µM) indicate the involvement of protein-tyrosine phosphorylation in this event. The data suggest that under hypoxic conditions when Na+,K+-ATPase activity is reduced, RBEC have the ability to increase K+ uptake through activation of Na+-K+-Cl- cotransport.
Résumé
Nous avons étudié l’effet de l’hypoxie sur la capture du potassium par des cultures de cellules endothéliales de capillaires cérébraux de rat en utilisant le radioélement 86 Rb+ comme traceur du potassium. L’incubation des cultures en milieu hypoxique (95% N2/ 5% CO2) pendant 24 heures réduit l’activité du transporteur Na K ATP- dépendant de 39% tandis qu’elle augmente le cotransport Na,K,C1 de 48%. Le traitement des cellules par l'oligomycine, un inhibiteur métabolique, conduit à une complète inhibition du transporteur Na,K et une augmentation simultanée de 100% du cotransport Na, Cl, K. L’oligomycine augmente aussi l’efflux de potassium. L’induction de l’activité du cotransport Na, K, Cl peut être inhibée par des inhibiteurs de protéine tyrosine kinase (génistéine, 50µM; herbimycine A, 10 µM) mais pas par des inhibiteurs de protéine kinase C (bisindolylmaléimide, 500 nM) ou de protéine kinase A (H8, 20 µM). Ceci semble montrer que la phosphorylation de protéines par des protéine kinases intervient dans l’induction de ce cotransporteur. ces résultats suggèrent que, soumises à des conditions d’hypoxie, les cellules endothéliales cérébrales ont la possibité de compenser la diminution de l’activité du transporteur Na K par l'induction de l’activité du cotransporteur Na K Cl.
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Kawai, N., McCarron, R.M., Spatz, M. (1996). Hypoxia Augments Na+-K+-Cl-Cotransport Activity in Cultured Brain Capillary Endothelial Cells of the Rat. In: Couraud, PO., Scherman, D. (eds) Biology and Physiology of the Blood-Brain Barrier. Advances in Behavioral Biology, vol 46. Springer, Boston, MA. https://doi.org/10.1007/978-1-4757-9489-2_39
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