Table 3

Binding properties of guanidines at hH2R-GsαS and gpH2R-GsαS expressed in Sf9 cell membranes

AgonistKhKl%RhKhGTPγSKlGTPγS%RhGTPγS
nM nM
hH2R-GsαS
5(IMP)64 (48–85)234 (167–327)
8(ARP)11 (6.2–18)461 (200–1055)63.7 (50.7–76.8)296 (216–404)
10(BU-E-48)7.2 (3.4–15.5)248 (129–475)46.0 (31.8–60.3)368 (288–469)
gpH2R-GsαS
5(IMP)27 (21–36)14.4 (3.4–62)236 (109–510)33.2 (5.8–60.7)
8(ARP)12 (5.6–25)152 (5–4700)78.4 (33.6–123.1)10 (3.6–28)164 (43–627)53.3 (19.6–87.1)
10(BU-E-48)0.02 (0.01–0.08)31 (20–47)43.9 (14.5–67.9)49 (41–60)

Agonist competition binding was determined as described underExperimental Procedures. The data shown in Fig. 7 were analyzed by nonlinear regression for best fit to monophasic or biphasic competition curves. Data shown are the means of four to six experiments performed in duplicate. Numbers in parentheses represent the 95% confidence intervals. K h and K ldesignate the dissociation constants for the high- and low-affinity state of H2Rs, respectively. %R h indicates the percentage of high-affinity binding sites. The corresponding values obtained in the presence of GTPγS (10 μM) are referred to asK hGTPγS, K lGTPγS and %R hGTPγS, respectively. If data were best fit to monophasic competition curves, data are listed underK l and K lGTPγS, respectively.