Cells were preincubated with either 1 μM β-PMA or 0.1 μM MCh for 30 min. Uptake assays were performed using 20 nM of radiolabeled substrate as described in “Methods.” Nonspecific uptake was determined by substituting choline for Na⁺ in KRH buffer. Atropine, 4-DAMP, pirenzepine and hexamethonium were added 10 min before the addition of MCh. Data are presented as mean ± S.E.M. of three separate experiments performed in duplicate. Asterisks denote significant difference as compared to control NE transport, P < .05 (Student’s t test).