The expanded pharmacological profile of histamine H2 receptor (H2R) species isoforms with respect to the interaction with new squaramide H2R ligands, in the GTP-ASE assay.

We comprehensively characterized the human (h), guinea pig (gp), canine (c) and rat (r) H2R species isoforms on Spodoptera frugiperda (Sf9) cell membranes expressing H2R-G(Salpha) with respect to the interaction with new ligands derived from squaramide. Antagonist potencies were determined in the GTPase assay. Non-linear curve fitting was performed using the computer program Prism 4.0 (GraphPad-Prism). An interesting result was obtained for the squaratepentylamine compound in comparison with famotidine. Furthemore, the analysis of the new squaramide ligands, under the same experimental conditions, at the four H2R species isoforms, indicates that the rH2R exhibits increased constitutive activity, compared with hH2R, gpH2R and cH2R. The present study validates the notion that quantitative comparison of species isoforms of GPCRs provides unique insights into the molecular mechanisms of GPCR activation.