Agonist-induced reduction in both the number of ml muscarinic receptors and the mRNA coding for the receptor protein was investigated in Chinese hamster ovary (CHO) cells which were transfected with the ml muscarinic receptor gene. Receptor concentration was measured by the specific binding of the muscarinic ligand, [3H]quinuclidinyl benzilate ([3H]QNB), and Northern blot hybridization analysis was used to evaluate the levels of receptor mRNA. Incubation of cells with 1 mM of the muscarinic agonist, carbamylcholine (CBC), for 24 h decreased receptor density and mRNA levels in cells by 65% and 73%, respectively. These results indicate that agonist-induced down-regulation of ml muscarinic receptors might be due to, at least in part, a decrease in receptor synthesis resulting from a reduction in the steady-state level of their mRNA.
Bibliographical noteFunding Information:
AcknowledgementTs:h is work wass upportedin partb y NIH Grants NS-25743a ndA G-07118a ndby contractD AAL-03-88-0078fr om the US Army ResearchO ffice. E.E.E. is the recipiento f a Research Career DevelopmentA ward from NIH (AG-00344).T he authors would like to thankM r Mike Gentrya nd MS Donna Betheaf or their invaluablea ssistance.
- Chinese hamster ovary cell
- Muscarinic receptor
- Northern blot analysis
- Receptor down-regulation
- mRNA regulation