Figure 4.

Effects of the α₁-adrenoceptor subtype selective antagonists 5-methylurapidil (5-MU) and chloroethylclonidine (CEC) on phenylephrine (PE) or A-61603 stimulated ERK1/2 in SMG-C10 cells. (A) Bar graph of α₁-adrenoceptor subtype selective antagonist effects on PE stimulated ERK1/2. Cells were incubated with either 5-MU for 30 min, CEC for 12 min, or 5-MU for 30 min followed by 5-MU plus CEC for 12 min. Samples treated with the irreversible antagonist CEC were extensively washed to remove non-bound antagonists. Cells were then treated with 10 μM PE for 7 min to stimulate ERK1/2. Data are plotted as % of Control (10 μM PE stimulated) ERK1/2. PE stimulated ERK1/2 was only inhibited by treatment with the α_1B-subtype selective antagonist CEC. (B) Mean concentration-response curves for A-61603 stimulation of ERK1/2 in the absence and the presence of an α_1A-adrenoceptor blocking concentration of 5-MU. SMG-C10 cells were incubated without or with 5-MU for 30 min and then stimulated for 7 min with increasing concentrations of A-61603. Each point on the concentration-response curve is the percentage of the maximal ERK1/2 stimulation produced by A-61603. The dashed line is the mean basal level of ERK1/2 activation in the absence of drugs. Only higher concentrations of A-61603 that stimulate α_1B-adrenoceptors activated ERK1/2 and this stimulation was not affected by α_1A-adrenoceptor blockade by 5-MU. All data are means ± S.E.M. of 4-5 individual experiments, each using different SMG-C10 cell cultures. *Significantly different from Control (10 μM PE alone), p < 0.05.