Blood-brain barrier mechanisms involved in brain calcium and potassium homeostasis.
This study examined the potential roles of the plasma membrane Ca2+-ATPase (PMCA) at the blood-CSF and blood-brain barriers in brain Ca2+ homeostasis and blood-brain barrier Na+/K+-ATPase subunits in brain K+ homeostasis. During dietary-induced hypo- and hypercalcemia (0.59+/-0.06 and 1.58+/-0.12 mM [Ca2+]) there was no significant change in choroid plexus PMCA (Western Blots) compared to normocalcemic rats (plasma [Ca2+]: 1.06+/-0.11 mM). In contrast, PMCA in cerebral microvessels isolated from hypocalcemic rats was 150% greater than that in controls (p<0.001). Comparison of the alpha3 subunit of Na+/K+-ATPase from cerebral microvessels isolated from hypo-, normo- and hyperkalemic rats (2.3+/-0.1, 3.9+/-0.1 and 7. 2+/-0.6 mM [K+]) showed a 75% reduction in the amount of this isoform during hyperkalemia. None of the other Na+/K+-ATPase isoforms varied with plasma [K+]. These results suggest that both PMCA and the alpha3 subunit of Na+/K+-ATPase at the blood-brain barrier play a role in maintaining a constant brain microenvironment during fluctuations in plasma composition.
Keep
R F
RF
Department of Surgery (Neurosurgery), University of Michigan, R5605 Kresge I, Ann Arbor, MI 48109-0532, USA.rkeep@umich.edu
Ulanski
L J
LJ
Xiang
J
J
Ennis
S R
SR
Lorris Betz
A
A
D000818:Animals; D001812:Blood-Brain Barrier / Q000502:physiology*; D001921:Brain / Q000098:blood supply / Q000201:enzymology / Q000502:physiology*; D002118:Calcium / Q000097:blood / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002196:Capillaries / Q000201:enzymology; D002831:Choroid Plexus / Q000201:enzymology; D006706:Homeostasis / Q000502:physiology*; D007527:Isoenzymes / Q000096:biosynthesis; D008297:Male; D011188:Potassium / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis
D007527:Isoenzymes; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D002118:Calcium