<Originals>SD-3212 blocks the inward rectifier potassium channel in guinea pig ventricular myocytes

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SD-3212 inhibited the calcium current, the sodium current and the muscarinic acetylcholine-receptor-operated potassium current. Inward rectifier potassium current (I_K1)is considered to contribute to both the repolarization phase of the ventricular action potential and the maintenance of the resting potential. However, the kinetics of blocking effects of multiple channel blockers on the I_K1 are unclear. In the present study, we investigated the effects of SD-3212 on the I_K1 channel in isolated guinea pig ventricular myocytes. Male guinea pig heart was perfused by Langendorff's method to prepare isolated ventricular myocytes using collagenase. Membrane currents of the isolated ventricular myocytes were recorded using the patch clamp technique. The peak and steadystate I_K1 were constantly inhibited by 100 μM SD-3212 irrespective of the potentials applied (the steady-state current was 36±4% blocked and the peak current was 28±2% blocked) under whole cell clamp conditions. Slope conductance 35±3pS was unchanged. SD-3212 (1mM) decreased the open probability from 92.5±0.8% in the control to 90.2±l.8% after 2 min, 85.5±2.4% after 3 min, 64.7±3.2% after 4 min, and to 22.6±2.4% after 5 min of exposure. Mean open time and mean closed time were unchanged after 5 min of exposure. SD-3212 decreased the open probability from 92.5±0.8% under control conditions to 91.6±1.4% in the presence of 100μM SD-3212,63.3±2.4% with 500μM SD-3212 and 22.6±3.l% with 1mM SD-3212 after 5 min of exposure under single channel recordings. In conclusions, SD-3212 blocks the I_K1 channels in a high dose concentration-dependent manner. SD-3212 blocks I_K1 channels via a hydrophobic pathway in accordance with a slow blocking mode.
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<Originals>SD-3212 blocks the inward rectifier potassium channel in guinea pig ventricular myocytes

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