Hypoxia Augments Na+-K+-Cl-Cotransport Activity in Cultured Brain Capillary Endothelial Cells of the Rat

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.