Muscarinic antagonist control of myopia: A molecular search forthe M1 receptor in chick

[摘要] Purpose: Pirenzepine, an M1 selective muscarinic antagonist, iseffective in slowing the progression of myopia in both humans andexperimental animals, including chick. As an M1 selective antagonist,pirenzepine is considered to mediate its effect through M1 receptors.However, there is currently no report of the M1 receptor in chicken.Therefore, if the mechanism of action of pirenzepine is similar acrossspecies, either the drug mediates its effect through a non-M1 mechanism,or M1 muscarinic receptors are present in chicken. The aim of thepresent study was to determine whether a genetic template for the M1receptor was expressed, or even present, in chick.Methods: Polymerase Chain Reaction (PCR), and Southern and northernblotting analyses were used to search for M1 mRNA in chick ocular andbrain tissues. PCR and Southern analyses were then used for searchingthe chick M1 gene and promoter. Appropriate rat positive controls wereincluded throughout the study.Results: Direct mRNA detection by northern analysis showed noevidence of M1 mRNA expression in the chick ocular and brain tissuesstudied. Identical results were obtained from PCR amplification and werefurther confirmed by Southern analysis. Similarly, no M1 gene orpromoter sequences were detected by PCR or Southern analyses. Ourmethods were validated in every case by a positive finding in equivalentrat tissue and by detection of M2 and M4 mRNA expression in chickretina.Conclusions: Findings in this study suggest that the chick does notpossess an M1 receptor. This finding is of primary interest to visionresearchers in that it suggests pirenzepine is unlikely to mediate itsinhibitory effect on the progression of myopia through an M1 receptor inchick. Alternative mechanisms of action are discussed.

[学科分类] 生物化学/生物物理