Figure 6.

Effect of PTX and CTX on SKF- or RAMH-induced ERK1/2 phosphorylation (P-ERK). SK-N-MC cells expressing H₃ receptors and D₁ receptors (SK-N-MC/D₁H₃) were treated with PTX (100 ng·mL⁻¹) for 16 h or with CTX (1 µg·mL⁻¹) for 30 min prior to the addition of the H₃ receptor agonist, RAMH (1 µmol·L⁻¹), or the D₁ receptor agonist, SKF 81297 (1 µmol·L⁻¹, SKF). ERK1/2 phosphorylation was determined as indicated in Methods. A representative Western blot is shown. The immunoreactive bands from four experiments were quantified, and values represent the mean ± SEM of fold increase of phosphorylation over basal levels found in untreated cells. Significant differences were calculated by Student's t-test for unpaired samples (*P < 0.05 and **P < 0.01). CTX, cholera toxin; ERK, extracellular signal-regulated kinase; RAMH, R-α-methyl histamine; PTX, Pertussis toxin; Veh, vehicle.