Diazoxide, a sulfonylurea receptor-transient receptor potential melastatin-4 (SUR-TRPM4) activator, did not increase voltage step-induced cation currents sensitive to 9-phenanthrol in detrusor smooth muscle (DSM) cells. A: depicted are representative current traces obtained for the control, 100 μM diazoxide, 100 μM 9-phenanthrol applied in the presence of 100 μM diazoxide, and washout of both diazoxide and 9-phenanthrol. The DSM cell was held at −74 mV and stepped to voltages ranging from −94 to +106 mV for 400 ms in 10-mV increments and returned to −74 mV. Gray dotted line and arrow indicate the level of steady-state current for the control at +106 mV. B: summary graph illustrates normalized responses for the control (n = 14, N = 12; n = no. of DSM cells patched, and N = no. of guinea pigs used), 100 μM diazoxide (n = 14, N = 12), 100 μM 9-phenanthrol added in the presence of 100 μM diazoxide (n = 5, N = 5), and washout (n = 6, N = 6) expressed as means with error bars for SE normalized to the control current density at +106 mV. Two-way ANOVAs revealed significant interactions for 1) the effects of voltage and diazoxide presence [control vs. 100 μM diazoxide, F(20, 260) = 2.906, P < 0.0001] and 2) the effects of voltage and the presence of 9-phenanthrol [9-phenanthrol + diazoxide vs. diazoxide vs. control in the same matched cells; n = 5, N = 5, F(40, 160) = 52.37, P < 0.0001]. Note that in two experiments (N = 2) the washout occurred after the addition of diazoxide only. The symbols (+, *, $, and #) indicate statistical differences (P < 0.05, two-way ANOVA post hoc Sidak multiple comparison test) at each voltage for: control vs. diazoxide (+), 9-phenanthrol + diazoxide vs. both diazoxide and control (*), 9-phenanthrol + diazoxide vs. control ($), and 9-phenanthrol+diazoxide vs. diazoxide (#). See Supplemental Fig. S8 for data displayed as current density vs. voltage relationships.