Subtype-specific regulation of muscarinic acetylcholine receptor expression and function in chicken retinal cells

GOIN, J.C.; NATHANSON, N.M.

San Francisco (California), USA

Congreso; 42nd American Society for Cell Biology Annual Meeting; 2002

American Society for Cell Biology

Muscarinic acetylcholine receptors (mAChR) have an important role in the processing of visual information and in retinal development. Three subtypes of mAChR, M2, M3 and M4 are expressed in the embryonic chick retina and have distinct but overlapping patterns of expression. The precise mechanisms that control this subtype-specific regulation of mAChR expression are still unknown. In this work, we examined the effect of long-term agonist exposure on mAChR expression and function in the chicken retina and investigated whether retinal M2, M3 and M4 mAChR are differentially regulated following prolonged agonist treatment. Long-term carbachol exposure induced a time- and concentration dependent decrease in M2, M3 and M4 muscarinic receptor numbers. Kinetic analyses revealed a first order process with similar rate constants for all three subtypes. Both the maximal decrease and the agonist potency for regulation of M3, were significantly higher than those for M2 and M4. Upon agonist removal, M2 and M4 numbers returned to control values, but M3 recovery was no higher than 40%. Receptor inactivation with a covalent alkylating antagonist demonstrated that the partial M3 protein was not due to decreased intrinsic basal rate of synthesis, suggesting that mAChR down-regulation occurs at the post-translational level. Prolonged carbachol exposure induced concomitant decreases in muscarinic-mediated inhibition of cAMP accumulation which were completely reversed. Sustained receptor activation also promoted significant decreases in muscarinic receptor-stimulated phosphoinositide turnover which were only partially reversed after agonist removal. These data demonstrate that mAChR expression and function are subtype-specific regulated by long-term agonist exposure in the embryonic chicken retina.