A cloned porcine renal calcitonin receptor couples to adenylyl cyclase and phospholipase C.

The signal transduction pathways of the recently cloned porcine kidney calcitonin (CT) receptor were evaluated. This receptor, when stably transfected into MC-3T3 cells, avidly bound salmon CT (SCT) [dissociation constant (Kd) = 4 nM]. Incubation with SCT resulted in a dose-dependent accumulation of adenosine 3',5'-cyclic monophosphate (cAMP) [50% effective concentration (EC50) = 0.02 nM] in transfected cells (referred to as PC-1 cells). Binding kinetics and cAMP dose response relationships were similar to those of the native receptor in LLC-PK1 cells. PC-1 cells also responded to calcitonin gene-related peptide (CGRP), but the EC50 value for cAMP accumulation was more than three orders of magnitude higher than for SCT. Exposure of PC-1 cells to SCT (5 nM to 1 microM) produced a dose-dependent rise in cytosolic free Ca2+ concentration ([Ca2+]i), whereas CGRP did not. The initial rise in [Ca2+]i was not dependent on extracellular Ca2+, suggesting that SCT induced release of Ca2+ from intracellular stores. SCT also increased inositol trisphosphate production in PC-1 cells. In conclusion, the cloned, transfected porcine CT receptor functionally couples to and activates both adenylyl cyclase and phospholipase C. This dual coupling is also a characteristic of the parathyroid hormone receptor, which has significant homology in amino acid sequence with the CT receptor.