Carrier-mediated uptake and release of histamine by cultured rat cerebral endothelial cells

The present study demonstrates that histamine could be taken up by and released from endothelial cells of brain capillaries. Incubation of cultured endothelial cells, with low (0.01-0.50 microM) concentrations of [3H]histamine, resulted in a rapid uptake of the amine. The uptake was saturable, Na(+)-dependent and yielded an apparent Km 0.3 +/- 0.02 microM and a Vmax 4.6 +/- 0.04 pmol/mg protein per min. After a 10-min incubation in a histamine-free medium, about 65% of [3H]histamine was released from the cells. Na(+)-deprivation and high K+, as well as the treatment of the cells with ouabain affected the release, resulting in significantly higher rates of the efflux. The ability of cerebral endothelial cells to take up histamine from both luminal and abluminal sides but to release it mainly luminally, may function as an important mechanism to protect the neural tissue from the harmful effects of this endogenous mediator of inflammation.