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Comparison of parathyroid hormone receptors in rat osteosarcoma cells and kidney

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Abstract

Parathyroid hormoneparathyroid-hormone-related peptide (PTHPTHrP) receptors have been characterized with chicken parathyroid hormone related protein [Tyr36]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 [125I][Tyr36]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 μM guanosine-5′-O-(3-thiotriphosphate). Rat [Nle8,18] 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 [125I]chPTHrP(1–36) was used. Specifically-labeled PTHPTHrP-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 PTHPTHrP 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.

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