Figure 5. Paraoxon does not alter expression of M2 muscarinic receptor protein.

Rat sympathetic neurons in cell culture (A) or Cos-7 cells transfected with full length cDNA encoding human M2 receptor (B) were treated with paraoxon (1–1000 nM) or vehicle (0.1% DMSO) for 24 hr in the absence or presence of carbachol (1 mM). Muscarinic receptor expression was determined as specific binding of [³H]-NMS (1 nM; surface receptors) or [³H]-QNB (1 nM; total receptors) in the absence (total) or presence (non-specific binding) of atropine (0.1 M). In both cell types, carbachol significantly decreased [³H]-NMS (A and B, open bars), but not [³H]-QNB (C, open bars) binding. In both sympathetic neurons (A) and Cos-7 cells (B), paraoxon had no effect on [³H]-NMS or [³H]-QNB binding in the absence or presence of carbachol. Data are represented as mean ± SE; n = 3–5.