Calcitonin receptor (CTR) is a class B G-protein coupled receptor (GPCR) that signals via activation of cAMP and protein kinase C (PKC). It is one of 15 human class B GPCRs. Apart from CTR, calcitonin receptor-like receptor (CTLR) is the only other B-class GPCR to bind calcitonin. To date, there are three known human CTR mRNA isoforms arising from alternative splicing.