Table 1

Binding characteristics of wild-type or mutant H2 receptors after transient expression in HEK-293 cells

H2ReceptorBmax[125I]APT,KDHistamine, Ki
fmol/mg protein nM μM
WT2526  ± 4160.53  ± 0.13369 ± 43
D115N246  ± 55* 0.22  ± 0.035 ± 3**/291 ± 240
(61 ± 14%/39 ± 14%)
D115A305  ± 60* 0.30  ± 0.0627 ± 8**/753 ± 554
(71 ± 20%/29 ± 20%)
R116N59  ± 5* N.D.1-a N.D.
R116A88  ± 83* N.D.N.D.

Cell homogenates of transiently transfected HEK-293 cells were incubated with increasing concentrations of [125I]APT in saturation experiments or with 0.3 nM [125I]APT and increasing concentrations of histamine in competition experiments. The dissociation constant (KD) and maximum number of binding sites (Bmax) were determined by using nonlinear fitting according to a one-site binding mode.Ki values were obtained from the respective IC50 values. For the arginine mutants theBmax was calculated assuming that theKD at these mutant receptors was comparable to theKD at the wild-type receptor. Data shown are mean ± S.E. from at least three independent experiments. Values in parentheses indicate the relative densities of the respective sites. The asterisks indicate a significant difference from HEK-293 cells expressing the wild-type receptor (see Materials and Methods).

  • 1-a N.D., not determined.