Cell volume regulation of cerebrovascular endothelium in vitro.

Regulation of cell volume as a fundamental cellular function of high biological priority was studied in cultured cerebrovascular endothelium. The use of a multiparameter flow cytometric system allowed simultaneous measurements of cell volume, viability, and membrane potential or intracellular pH. Endothelium, the cellular constituent of the blood-brain barrier (BBB), swells immediately on exposure to low osmolality. This is associated with membrane depolarization and a fall of intracellular pH. Within 30-60 min, cell volume and membrane potential recover completely, although the extracellular osmolality is kept low. Intracellular pH does not normalize fully. Measurements of intracellular K+ and Na+ concentrations reveal their involvement in the regulatory process. The findings strongly suggest that the cerebrovascular endothelium has a highly effective built-in capacity for homeostatic control essential for normal BBB function.