Distinct recognition of OX1 and OX2 receptors by orexin peptides

In this study, we have compared the abilities of orexin-A and orexin-B and variants of orexin-A to activate different Ca2 responses (influx and release) in human OX1 and OX2 receptor-expressing Chinese hamster ovary cells. Responses mediated by activation of both receptor subtypes with either orexin-A or-B were primarily dependent on extracellular Ca2, suggesting similar activation of Ca2 influx as we have previously shown for orexin-A and OX1 receptors. Amino acid-wise truncation of orexin-A reduced its ability to activate OX1 and OX2 receptors, but the response mediated by the OX2 receptor was more resistant to truncation than the response mediated by the OX1 receptor. We also performed a sequential replacement of amino acids 14 to 26 with alanine in the truncated orexin-A variant orexin-A14–33. Replacement of the same amino acids produced a fall in the potency for each receptor subtype, bu