Sodium Transport from Blood to Brain: Inhibition by Furosemide and Amiloride

Abstract

Brain Na uptake in vivo was studied in cats using a modified intracarotid bolus injection technique in which the uptake of 22Na+ was compared with that of the relatively impermeable molecule, [3H]L-glucose. At a Na+ concentration of 1.4 mM, Na+ uptake was 1.74 .+-. 0.07 times greater than L-glucose uptake. This decreased to 1.34 .+-. 0.04 at 140 mM Na+, indicating saturable Na+ uptake. Relative Na+ extraction was not affected by pH but was inhibited by amiloride (Ki = 3 .times. 10-7 M) and by 1 mM furosemide. The effects of these 2 inhibitors were additive. Brain uptake of 86Rb+, a K+ analog, was measured to study interaction of K+ with Na+ transport systems. Relative 86Rb+ extraction was also inhibited by amiloride; it was not inhibited by furosemide. Apparently there are 2 distinct transport systems that allow Na+ to cross the luminal membrane of the brain capillary endothelial cell. These transport systems could play an important role in the movement of Na+ from blood to brain.