The mechanism of reversible osmotic opening of the blood-brain barrier: role of intracellular calcium ion in capillary endothelial cells.
Despite clinical and experimental interest in the osmotic opening of the blood-brain barrier (BBB), the mechanism underlying the phenomenon remain undetermined. The aim of this study is to investigate the mechanism of intracellular Ca2+ change in brain microvascular endothelial cells subjected to hyperosmotic stress. Cultured rat brain capillary endothelial cells were obtained by two-step enzymatic purification. Intracellular Ca2+ was measured by a confocal laser scanning microscope. After exposing the endothelial cells to 1.4 M mannitol for 30 seconds, the change of intracellular Ca2+ concentration was monitored. Intracellular Ca2+ concentration increased rapidly and reached its peak value within 10 seconds after the application of mannitol. The Ca2+ concentration returned to the basal level within 200 seconds. A calcium channel blocker nifedipine (100 microM, 10 microM) did not block the increase. A specific blocker (KB-R7943) of Na+/Ca2+ exchange did not affect the rapid elevation of intracellular Ca2+. However, it blocked the return phase almost completely. The results indicated that the Na+/Ca2+ exchanger pumped out the increased intracellular Ca2+ during the return phase. Reversible osmotic disruption and reconstruction of the BBB is not due to simple mechanical shrinkage of the endothelial cells but is due to the intracellular Ca(2+)-activated complex mechanism. The manipulation of the reconstruction phase, which depends on Na+/Ca2+ exchanger, may have clinical implications.
Nagashima
T
T
Department of Neurosurgery, Kobe University School of Medicine, Japan.
Ikeda
K
K
Wu
S
S
Kondo
T
T
Yamaguchi
M
M
Tamaki
N
N
D000818:Animals; D001812:Blood-Brain Barrier / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology*; D008297:Male; D018613:Microscopy, Confocal; D009997:Osmotic Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D015290:Second Messenger Systems / Q000502:physiology*
D002118:Calcium