ABSTRACT
Abstract-To elucidate the functional importance of histamine at the blood-brain barrier (BBB), we discuss recent findings regarding the transport characteristics and metabolism of L-histidine, a precursor of histamine, in cultured rat brain microvascular endothelial cells (BMECs) which are major structural components of the BBB. L-Histidine was uptaken by rat BMECs via both Na+-dependent system N and Na+-independent system L transporters. Zinc ion had an enhancing effect on the BBB transport of L-histidine. L-Histidine is biotransformed to histamine by L-histidine decarboxylase (HDC). The presence of HDC protein and the expression of HDC mRNA were confirmed in rat BMECs, and the HDC activity of the BMECs was estimated to be 0.14 ± 0.05 pmol/mg protein/min. These findings indicated that L-histidine uptaken by rat BMECs was shown to be converted to histamine, suggesting that HDC may play an important role in the regulation of paracellular permeability through tight junctions in BBB.
