Berman N D, Wang L Y, Ahmed A
Department of Medicine, University of Toronto, Ontario.
Can J Cardiol. 1990 Nov;6(9):423-30.
Using standard microelectrode techniques, the authors compared the effects of 15 to 125 microM concentrations of mexiletine, 31 to 500 microM concentrations of sotalol and 15 to 125 microM of mexiletine combined with 125 microM sotalol, on the beat-to-beat action potential duration and refractoriness of porcine papillary muscles and Purkinje fibres stimulated by 30 beat trains at a frequency of 1 Hz. Sotalol alone prolonged action potential duration and effective refractory period without altering their ratio. Mexiletine shortened action potential duration while prolonging refractoriness. When the two drugs were combined, action potential duration was shortened to the same extent as with mexiletine alone, but refractoriness, particularly in papillary muscle, was further prolonged. These changes suggest additive inhibition of the sodium window current by both drugs. Purkinje action potential duration was longest in the first beat of the train, while in papillary muscle, this beat was shortest. Exposure to either or both drugs eliminated the prolongation of duration of the first beat of the train in Purkinje fibre. Thus, the phenomenon of restitution, which prolongs the duration of the first beat after a long diastolic interval, appears also to be related to the sodium window current.
作者采用标准微电极技术，比较了15至125微摩尔浓度的美西律、31至500微摩尔浓度的索他洛尔以及15至125微摩尔美西律与125微摩尔索他洛尔联合使用时，对以1赫兹频率的30次搏动序列刺激的猪乳头肌和浦肯野纤维逐搏动作电位持续时间和不应期的影响。单独使用索他洛尔可延长动作电位持续时间和有效不应期，而不改变它们的比值。美西律缩短动作电位持续时间，同时延长不应期。当两种药物联合使用时，动作电位持续时间缩短至与单独使用美西律时相同的程度，但不应期，尤其是在乳头肌中，进一步延长。这些变化表明两种药物对钠窗电流具有相加抑制作用。浦肯野纤维动作电位持续时间在序列的第一个搏动中最长，而在乳头肌中，这个搏动最短。暴露于其中一种或两种药物均可消除浦肯野纤维序列第一个搏动持续时间的延长。因此，在长舒张间期后延长第一个搏动持续时间的复极现象似乎也与钠窗电流有关。
