Table 1

Comparison of antagonist binding to human PTH1 and PTH2 receptors

LigandPTH1 ReceptorPTH2 ReceptorPTH2 IC50/PTH1 IC50
−logIC50 (IC50, nM)Pseudo Hill Slope−logIC50 (IC50, nM)Pseudo Hill Slope
TIP39(7-39)8.21  ± 0.071-a 1-b 1.30  ± 0.167.02  ± 0.040.98  ± 0.0116
(6.2)(95)
[d-Trp12,Tyr34]PTH(7-34)7.35  ± 0.221-a 1.10  ± 0.036.88  ± 0.060.96  ± 0.142.9
(45)(130)
PTHrP(7-34)7.19  ± 0.081-b 0.93  ± 0.246.76  ± 0.051.05  ± 0.162.9
(65)(170)

Radioligand binding to membranes prepared from HEK293 cells stably expressing the receptors was measured as described underMaterials and Methods. Data were fitted to a four-parameter logistic equation (eq. 1) to obtain estimates of logIC50 and pseudo Hill slope. Values are mean ± S.E.M. from three experiments except for the values for [d-Trp12,Tyr34]PTH(7-34) at the PTH2 receptor which are mean ± range (n = 2).

  • Statistical significance between the mean IC50 value for the three peptides at the PTH1 receptor was tested by single-factor analysis of variance followed by post hoc analysis with the Newman-Keuls test:

  • ↵1-a  values are significantly different (P < .01);

  • ↵1-b  P < .005.