Expression of histamine receptor Hrh3 and Hrh4 in rat brain endothelial cells.

BACKGROUND AND PURPOSE: Brain vascular endothelial cells express histamine H1 and H2 receptors, which regulate brain capillary permeability. We tested the hypothesis that also H3 and H4 receptor are expressed in these cells and may thus play roles in permeability regulation. EXPERIMENTAL APPROACH: An immortalized rat brain endothelial cell line RBE4 was used to assess the presence of H3R and H4R. RT-PCR and sequencing were used to identify the receptor mRNAs. Receptor stimulation was done with histamine and immepip, and specific inverse agonists/antagonists ciproxifan and JNJ 7777120 were used to block H3R and H4R, respectively. KEY RESULTS: RT-PCR on mRNA extracted from cultured immortalized RBE4 cells revealed two Hrh4 transcripts, one full length H4 receptor (CDS 1173bp), and one with a 164bp deletion. Also two Hrh3 receptor isoform mRNAs were expressed in RBE4 cells, and sequencing showed them to be the full-length H3R and the 144 bp deletion form. Both histamine and immepip (H3R and H4R agonist) activated the Erk1/2 MAPK pathway in cultured brain microvessel endothelial cells and in vivo in brain blood vessels through histamine H4 receptor activation. In RBE4 cells, the H4R specific inverse agonists / antagonist JNJ 7777120 but not ciproxifan, the H3 receptor antagonist, dose dependently blocked the effect. CONCLUSIONS AND IMPLICATIONS: The results show that both Hrh3 and Hrh4 receptor are expressed in rat brain endothelial cells, and activation of H4R activates the Erk1/2 cascade. H3R and H4R in endothelial cells are potentially important for regulation of BBB permeability, including trafficking of immunecompetent cells. © 2013 The Authors. British Journal of Pharmacology © 2013 The British Pharmacological Society.