Figure 4
Effect of D 4 receptor on insulin receptor expression in A10 cells. A. Concentration-dependent effect of the D4 receptor agonist PD168077 on insulin receptor protein expression in A10 cells. A10 cells were incubated with insulin in the absence or presence of varying concentrations of the D4 receptor agonist PD168077 (PD, 10-10 mol/L - 10-6 mol/L) for 24 hrs. Insulin receptor expression was determined by immunoblotting. Distilled water (dH2O), instead of insulin, was used as control. Results are expressed as the ratio of insulin receptor to α-actin densities (n = 5, *P < 0.05 vs. control). B. Time-course of the effect of the D4 receptor agonist PD168077 on insulin receptor protein expression in A10 cells. The cells were incubated at the indicated times with PD168077 (PD, 10-7 mol/L). dH2O, instead of insulin, was used as control. Results are expressed as the ratio of insulin receptor to α-actin densities (n = 5, *P < 0.05 vs. control). C and D. Specificity of D4 receptor effect on insulin receptor expression in A10 cells. A10 cells were incubated with the indicated reagents: (dH2O [Control], PD, PD168077, 10-7 mol/L, L,L745870, 10-7 mol/, or PD + L) for 24 hrs. The insulin receptor protein or mRNA expressions were determined by immunoblotting (C) or RT-PCR (D). Results are expressed as the ratio of insulin receptor (as a fraction of 100%) to α-actin for immunoblotting or β-actin densities for RT-PCR (as a fraction of 100%) individually (n = 5, *P < 0.05 vs. others).