Pharmacological characterization of a receptor for calcitonin gene‐related peptide on rat, L6 myocytes

The L6 myocyte cell line expresses high affinity receptors for calcitonin gene‐related peptide (CGRP) which are coupled to activation of adenylyl cyclase. The biochemical pharmacology of these receptors has been examined by radioligand binding or adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) accumulation.In intact cells at 37°C, human and rat α‐ and β‐CGRP all activated adenylyl cyclase with EC50s of about 1.5 nm. A number of CGRP analogues containing up to five amino acid substitutions showed similar potencies. In membrane binding studies at 22°C in 1 mmMg2+, the above all bound to a single site with IC50s of 0.1–0.4 nm.The fragment CGRP(8–37) acted as a competitive antagonist of CGRP stimulation of adenylyl cyclase with a calculatedKdof 5 nm. TheKddetermined in membrane binding assays was lower (0.5 nm).The N‐terminal extended human α‐CGRP analogue Tyro‐CGRP activated adenylyl cyclase and inhibited [125I]‐iodohistidyl‐CGRP binding less potently than human α‐CGRP (EC50for cyclase = 12 nm, IC50for binding = 4 nm).The pharmacological profile of the L6 CGRP receptor suggests that it most closely resembles sites on skeletal muscle, cardiac myocytes and hepatocytes. The L6 cell line should be a stable homogeneous model system in which to study CGRP mechanisms and pharmacology.