Effects of two truncated forms of human calcitonin-gene related peptide: implications for receptor classification

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Abstract

We investigated the possibility that human α-calcitonin-gene related peptide (CGRP)-(8–37) and human βCGRP-(8–37) show some selectivity as antagonists of CGRP1 and CGRP2 receptor-mediated responses. Bindings assays showed that human αCGRP, human αCGRP-(8–37) and human βCGRP-(8–37) showed high affinity (in the nanomolar concentration range) for CGRP receptors expressed in SK-N-MC cells and also in rat brain membrain preparations. Both human αCGRP-(8–37) and human βCGRP-(8–37) were potent antagonists of human αCGRP-stimulated cAMP accumulation in SK-N-MC cells. However, both human αCGRP-(8–37) and human βCGRP-(8–37) were weakly effective in antagonizing human αCGRP-stimulated responses in guinea-pig atria and rat vas deferens. In rat vas deferens, but not guinea-pig atria, the effects of human αCGRP and human αCGRP-(8–37) (but not human βCGRP-(8–37)) were potentiated by thirophan. Neither human α- nor human βCGRP-(8–37) showed selectivity for supposedly CGRP1 and CGRP2 receptor-mediated responses. Furthermore, differences in the effects of the truncated CGRP analogues may reflect differences in enzyme distribution rather than the existence of CGRP receptor subtypes.

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