Fig. 4.

Examples of effect of perfusion of NFA and CK on the action of KN93 on the smooth muscle membrane potential and ETP on the same cell. A: during perfusion of NFA, smooth muscle had membrane potential of −69 mV and ETP of 14.5 mV. Addition of KN93 did not change either the membrane potential or the ETP, suggesting that NFA blocked the action of KN93 by saturation block of Cl⁻ channels. B: after perfusion of cromakalim, the smooth muscle was hyperpolarized (membrane potential: −78 mV) and had small amplitude ETP of 3.7 mV. Addition of KN93 further hyperpolarized the membrane by 8 to −86 mV, and increased the amplitude of the ETP, suggesting that CK hyperpolarization does not block the action of KN93, which can still act to close Cl⁻ channels (membrane potential values in representative strips are indicated).