Histamine receptor expression in human renal tubules: a comparative pharmacological evaluation.

Objective and Design: The aim of this study is to evaluate the expression of the histamine receptors, particularly focusing on the H4R in human renal tubules.
Material: The ex vivo evaluation was carried on specimens from human renal cortex. Primary and immortalized tubular epithelial cells (TECs) and the HK-2 cell line were used as in vitro models.
Treatment: Cells were pretreated for 10 min with chlorpheniramine maleate 10 μM (H1R antagonist), ranitidine 10 µM (H2R antagonist), GSK189254 1 µM (H3R antagonist) or JNJ7777120 10 µM (H4R antagonist), and then exposed to histamine (3 pM-10 nM) for 30 min.
Methods: The ex vivo evaluation on specimens from human renal cortex was performed by immunohistochemistry. The expression of histamine receptors on primary and immortalized TECs and the HK-2 cell line was evaluated at both gene (RT-PCR) and protein (immunocytofluorescence) levels. The pharmacological analysis was performed by TR-FRET measurements of second messenger (IP3 and cAMP) production induced by histamine with or without the selective antagonists.
Results: Our data revealed the presence of all histamine receptors in human tubules; however, only TECs expressed all the receptors. Indeed, histamine elicited a sigmoid dose-response curve for IP3 production, shifted to the right by chlorpheniramine maleate, and elicited a double bell-shaped curve for cAMP production, partially suppressed by the selective H2R, H3R and H4R antagonists when each added alone, and completely ablated when combined together.
Conclusions: Herein, we report the identification of all four histamine receptors in human renal tubules.