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 alpha 3 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 alpha 3 subunit of Na+/K+-ATPase at the blood-brain barrier play a role in maintaining a constant brain microenvironment during fluctuations in plasma composition. (C) 1999 Elsevier Science B.V. All rights reserved.