ISOFORMS OF THE RAT CALCITONIN RECEPTOR - CONSEQUENCES FOR LIGAND-BINDING AND SIGNAL-TRANSDUCTION

Abstract

Two rat calcitonin (CT) receptor isoforms; C1a and C1b, are identical except for the presence of a 37-amino acid insert in the second extracellular domain of C1b. The functional consequences of this insert were examined after stable expression of these receptors into HEK-293 cells. In binding competition studies, dissociation of [125I]salmon CT ([125I]sCT) from C1b cells was rapid and complete, in contrast to dissociation from C1a cells, which was slow and incomplete, as seen with other CT receptor preparations. In these studies, C1a receptors displayed high affinity for salmon CT (Kd, 0.5 +/- 1.3 nM) and a slightly lower affinity for pig CT. Human CT competed more weakly for binding of [125..