Transport of carnitine in RBE4 cells - an in vitro model of blood-brain barrier

Accumulation of carnitine was studied in immortalized rat brain capillary endothelial cells RBE4, as an in vitro model of blood-brain barrier. Both uptake and efflux phenomena were found independent on [Na+] gradient. A quick acylation of carnitine in RBE4 cells was observed, especially leading to formation of long-chain acylcarnitines (46%), while 38% of the accumulated compound was found in the form of free carnitine. Exposure of basolateral membrane to carnitine-free medium induced a quick efflux, leaving, however, about 50% of accumulated carnitine inside the cells. The process of accumulation was found to be sensitive to butyrobetaine and cysteine, but not to choline or Hemicholinium-3, pointing to sterical demands of a transporter responsible for carnitine uptake.