Sodium transport from blood to brain: inhibition by furosemide and amiloride.

Brain sodium uptake in vivo was studied 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 X 10(-7) M) and by 1 mM furosemide. The effects of these two inhibitors were additive. Brain uptake of 86Rb+, a K+ analogue, was measured to study interaction of K+ with Na+ transport systems. Relative 86Rb+ extraction was also inhibited by amiloride; however, it was not inhibited by furosemide. The results suggest the presence of two 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.