EXPRESSION OF MUSCARINIC RECEPTOR SUBTYPE MESSENGER-RNA IN THE HUMAN CILIARY MUSCLE

Purpose. To investigate the expression of the muscarinic receptor (mAC hR) subtypes (m1, m2, m3, m4, and m5) in the human ciliary muscle. Met hods. cDNA probes specific for the m1 to m5 subtypes were used to char acterize the expression of subtype-specific mRNAs by in situ hybridiza tion and Northern blot analysis on a cell line derived from human cili ary muscle tissue (H7CM), sectioned tissue from four donors, and fresh human ciliary muscle tissue from three donors. Results. Messenger RNA for m2, m3, and m5 was detected by in situ hybridization and Northern blot analysis in the H7CM cell line and in human ciliary muscle tissu e from the donors. In human ciliary muscle tissues, the expression of mRNA of the m2 and m3 subtypes was more prominent in the circular port ion than in the longitudinal portion. In contrast, mRNA for the m5 sub type was greater in the longitudinal portion than in the circular port ion. Additionally, Northern blot analysis showed that m1 and m4 were e xpressed in ciliary muscle tissue.Conclusion. These studies show that the human ciliary muscle definitely expresses the mRNA of subtypes m2, m3, and m5, and may also express the mRNA of m1 and m4. Although the expression of mRNA for the m2, m3, and m5 subtypes differed between th e circular and longitudinal portions of the ciliary muscle, the strong expression of all three subtypes of muscarinic receptors by both port ions demonstrates that the differential distribution of muscarinic sub types probably is not responsible for the dissociation between outflow facility and accommodation that can occur under certain conditions.