Figure 1.

Time-course of agonist-promoted down-regulation of mAChRs in MEF. MEF wt cells were transfected with eGFP-M₁ (◆) or HA-M₂ (■) mAChR. 24 hr following transfection, cells were treated with 1 mM carbachol for the indicated time. Down-regulation was determined using [³H]-QNB binding (fmol/mg protein) in crude membranes as described in methods. The M₁ mAChR displays nearly threefold the down-regulation of the M₂ subtype over the same time course. Data are expressed as percent down-regulation compared to t = 0 control and are presented as mean ± standard error of the mean for three independent experiments with duplicate data points. Total mAChR expressed (fmol/mg) at t = 0 was 4000 for both M₁ and M₂ mAChRs.