Sodium transport in capillaries isolated from rat brain.
Brain capillary endothelial cells form a blood-brain barrier (BBB) that appears to play a role in fluid and ion homeostasis in brain. One important transport system that may be involved in this regulatory function is the Na+, K+-ATPase that was previously demonstrated to be present in isolated brain capillaries. The goal of the present study was to identify additional Na+ transport systems in brain capillaries that might contribute to BBB function. Microvessels were isolated from rat brains and 22Na+ uptake by and efflux from the cells were studied. Total 22Na+ uptake was increased and the rate of 22Na+ efflux was decreased by ouabain, confirming the presence of Na+, K+-ATPase in capillary cells. After inhibition of Na+, K+-ATPase activity, another saturable Na+ transport mechanism became apparent. Capillary uptake of 22Na+ was stimulated by an elevated concentration of Na+ or H+ inside the cells and inhibited by extracellular Na+, H+, Li+, and NH4+. Amiloride inhibited 22Na+ uptake with a Ki between 10(-5) and 10(-6) M but there was no effect of 1 mM furosemide on 22Na+ uptake by the isolated microvessels. These results indicate the presence in brain capillaries of a transport system capable of mediating Na+/Na+ and Na+/H+ exchange. As a similar transport system does not appear to be present on the luminal membrane of the brain capillary endothelial cell, it is proposed that Na+/H+ exchange occurs primarily across the antiluminal membrane.
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D001812:Blood-Brain Barrier; D001921:Brain / Q000098:blood supply*; D002196:Capillaries / Q000378:metabolism; D004727:Endothelium / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011522:Protons; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D011522:Protons; D010042:Ouabain; D000584:Amiloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase