Human muscarinic receptors expressed in A9L and CHO cells: activation by full and partial agonists.
1. A comparative study of receptor activation by ten full and partial muscarinic agonists was undertaken on the five subtypes of human muscarinic receptors expressed at similar receptor densities in Chinese hamster ovary (CHO-K1) cells. In addition, m1, m2 and m3 receptors were expressed in mouse fibroblast A9L cells in order to compare the influences of cell type on agonist activation of these receptors. 2. Receptor-effector coupling efficiencies were greater in CHO than A9L cells and agonists displayed greater potencies and similar or greater intrinsic activities at CHOm1 and CHOm3 than A9Lm1 and A9Lm3 receptors. Although m2 receptor density was 6 fold higher in A9L than CHO cells, carbachol elicited significantly greater inhibition of adenosine 3':5'-cyclic monophosphate (cyclic AMP) formation in CHOm2 cells. These data suggest that not only receptor density but receptor-effector coupling and/or coupling efficiencies play significant roles in agonist-induced responses. 3. In CHO cells, receptor-effector coupling efficiencies were m3 = m1 > m5. Although CHOm5 receptors were the least efficiently coupled, some partial agonists displayed higher intrinsic efficacies at m5 than m3 receptors suggesting that, in CHO cells, m5 and m3 receptors may activate different G proteins and/or effectors to stimulate inositol monophosphate ( IP1) formation. 4. McN-A-343 was a functionally selective m4 agonist. It had little or no agonist activity at m3 receptors expressed in either A9L or CHO cells.(ABSTRACT TRUNCATED AT 250 WORDS)[1]References
- Human muscarinic receptors expressed in A9L and CHO cells: activation by full and partial agonists. Richards, M.H., van Giersbergen, P.L. Br. J. Pharmacol. (1995) [Pubmed]
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