Fig. 2. Muscarinic receptor–mediated tyrosine phosphorylation and activation of extracellular signal-regulated kinase (ERKs). PC12 cells were treated with the absence (−) or the presence (+) 50 μM atropine (Atro) for 10 min and then stimulated with 1 mM carbachol for 2 min. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis and Western blot analysis with anti-phosphotyrosine antibody or anti-ERK antibody were performed. ( A ) The presence of atropine abolished tyrosine phosphorylation of 44- and 42-kd proteins. The molecular mass markers of p44 and p42 expressed in kilodaltons are indicated on the left. ( B ) Atropine completely blocked the activation of ERK1 and ERK2. The upper two arrows on the left indicate ERK1 ( 
, active forms of ERK1) and the lower two indicate ERK2 ( 
, active forms of ERK2).
