Characterization of a putative calcitonin receptor in IMR 32 human neuroblastoma cells

In this study we characterized calcitonin (CT) receptors in human neuroblastoma IMR 32 cells. Saturation binding assays indicated that [ 125I]-human CT bound with high affinity to IMR 32 cell membranes ( K d=253.6 pM; B max=3.84 fmol/mg protein). In competition binding studies, human adrenomedullin displayed high affinity for these sites (IC 50=30 nM) whereas human α calcitonin-gene related peptide ( αCGRP; IC 50=145 nM) and human amylin (IC 50=415 nM) showed lower affinity. These peptides increased cAMP levels in viable cells; the relative potencies were: human CT > human adrenomedullin > human αCGRP ≥ human amylin. The expression of mRNA coding for the published sequences of the human calcitonin receptor and of the human calcitonin receptor-like receptor was evaluated by reverse transcriptase- polymerase chain reaction. Electrophoretic analysis did not confirm the occurrence of mRNA coding for the above mentioned receptors in these cells. This study suggests the presence of a novel, putative CT receptor in IMR 32 cells.