COMPARISON OF PARATHYROID-HORMONE RECEPTORS IN RAT OSTEOSARCOMA CELLS AND KIDNEY

Parathyroid hormone/parathyroid-hormone-related peptide (PTH/PTHrP) receptors have been characterized with chicken parathyroid hormone related protein [Tyr(36)]chPTHrP(1-36)amide (chPTHrP(1-36)) as radioligand in rat UMR-106 osteosarcoma (UMR) cells and in rat renal cortical membranes (RCM). Binding of 125 pM [I-125][Tyr(36)]chPTHrP(1-36) was displaced by chPTHrP(1-36) with ID50 values of 2.6 +/- 0.22 nM (mean +/- S.E.) and 0.9 +/- 0.03 nM in UMR cells and RCM, respectively. ID50 values in membranes from UMR cells and RCM were the same in the presence and absence of 10 mu M guanosine-5'-O-(3-thiotriphosphate). Rat [Nle(8,18)] PTH(1-34) was 5-fold more potent than chPTHrP(1-36) in RCM, but not in UMR cells. Hill coefficients derived from binding inhibition were 0.93 and 0.35 in UMR and RCM, respectively. For affinity labeling, N-hydroxysuccinimidyl-4-azidobenzoate-modified [I-125]chPTHrP(1-36) was used. Specifically-labeled PTH/PTHrP-binding proteins had a molecular mass of 83 kDa in UMR cells and RCM. Treatment with N-endoglycosidases lowered the molecular mass of chPTHrP binding proteins to 54 kDa in UMR and RCM. In conclusion, skeletal UMR-106 cells and renal cortical membranes of the rat reveal PTH/PTHrP receptors with no apparent tissue specific differences in molecular mass of the polypeptide backbone and polysaccharide chains. Higher affinity of rat PTH(1-34) binding and lower Hill coefficients in kidney compared to bone are consistent with tissue specific receptor-ligand interactions.