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

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Abstract
1 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. 2 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 mm Mg2+, the above all bound to a single site with IC50s of 0.1–0.4 nm. 3 The fragment CGRP(8–37) acted as a competitive antagonist of CGRP stimulation of adenylyl cyclase with a calculated Kd of 5 nm. The Kd determined in membrane binding assays was lower (0.5 nm). 4 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 (EC50 for cyclase = 12 nm, IC50 for binding = 4 nm). 5 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.

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