Recent advances in understanding brain capillary function.

The endothelial cells in brain capillaries form a blood-brain barrier which limits and controls the movement of solutes between blood and brain. These cells contain continuous tight junctions and exhibit a low rate of pinocytosis, resulting in formation of a permeability barrier to macromolecules and many polar compounds. However, brain capillary endothelial cells also contain specialized transport systems that facilitate blood-to-brain transfer of some solutes and actively pump other solutes from brian to blood. Several investigators have developed methods to isolate microvessels from brain or to grow brain capillary endothelial cells in tissue culture. This review summarizes progress made with these model systems and discusses their usefulness in increasing our knowledge of brain capillary function.