Stimulation and inhibition of window contraction. A: Representative example of isometric contractions of a segment depolarized with cumulative K+ concentrations in the absence (C, black) and presence of 30 nM BAY K8644 (B, blue), 200 nM levcromakalim (L, green), or their combination (B + L, red). B: “Steady-state” force at each step was plotted as function of [K+] with values at 50 mM K+ as 100%. Results show mean ± s.e.m, n = 4. *, ***: P<0.05, 0.001 versus control. C: Change of basal tension (Δ force in mN) for repolarization and depolarization of Vm by changing extracellular K+ to attain Vm within the physiological range for non-stimulated VSMCs (K+ from 5.9 mM to 2 (white) or 10 (grey) or 15 (black) mM) in control conditions (C) and in the presence of 30 nM BAY K8644 (B). Instead of the actual K+ concentration, the estimated Vm of the VSMCs is indicated: -77 mV for 2 mM, -66 mV for 5.9 mM, (not shown), -59 mV for 10 mM and −51 mV for 15 mM K+. Results show mean ± s.e.m, n = 5. *, **, ***: P<0.05, 0.01, 0.001 versus 5.9 mM K+.