Carmeliet E
Laboratory of Physiology, University of Leuven, Belgium.
Circ Res. 1993 Nov;73(5):857-68. doi: 10.1161/01.res.73.5.857.
A voltage-clamp analysis of the effect of almokalant on the delayed rectifier K+ current (IK) was made in rabbit ventricular myocytes. The two-suction pipette method was used, and appropriate voltage-clamp protocols were used to study more specifically use dependence, block development, and recovery from block. Almokalant interacted with the IK in two ways: it shifted the activation curve in the hyperpolarizing direction (stimulatory effect) and blocked the open IK channel in a use-dependent way (inhibitory effect). For 2-second voltage clamps to +20 mV, half-maximum block was obtained at 5 x 10(-8) mol/L, with a Hill coefficient of 1.76. Use-dependent block was related to an open-channel block that occurred at 0 mV with a time constant of 1.07 second and a rather slow recovery from block: at -50 mV, recovery time constant was approximately 10 seconds; at -75 mV, recovery was practically absent. The absence of an important recovery at negative membrane potentials is consistent with the hypothesis of the drug being trapped in the channel. A limited frequency-dependent block could be demonstrated. Use-dependent unblock was demonstrated by a rapid recovery from block during stimulation following complete washout of the drug. It is concluded that almokalant shifts the activation curve of IK in the hyperpolarizing direction, blocks the open channel, and is trapped by the closure of the activation gate.
在兔心室肌细胞中对almokalant对延迟整流钾电流（IK）的影响进行了电压钳分析。采用双吸移液管法，并使用适当的电压钳方案更具体地研究使用依赖性、阻断发展和从阻断中恢复的情况。Almokalant以两种方式与IK相互作用：它使激活曲线向超极化方向移动（刺激作用），并以使用依赖性方式阻断开放的IK通道（抑制作用）。对于2秒的+20 mV电压钳，在5×10（-8）mol/L时获得半数最大阻断，希尔系数为1.76。使用依赖性阻断与在0 mV发生的开放通道阻断有关，时间常数为1.07秒，且从阻断中恢复相当缓慢：在-50 mV时，恢复时间常数约为10秒；在-75 mV时几乎没有恢复。在负膜电位下没有重要的恢复与药物被困在通道中的假设一致。可以证明存在有限的频率依赖性阻断。通过在药物完全洗脱后的刺激期间从阻断中快速恢复来证明使用依赖性解阻断。结论是almokalant使IK的激活曲线向超极化方向移动，阻断开放通道，并被激活门的关闭所捕获。
