Main M C, Bryant S M, Hart G
Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, UK.
Exp Physiol. 1998 Nov;83(6):747-61. doi: 10.1113/expphysiol.1998.sp004156.
Regional differences in action potential characteristics and membrane currents were investigated in subendocardial, midmyocardial and subepicardial myocytes isolated from the left ventricular free wall of guinea-pig hearts. Action potential duration (APD) was dependent on the region of origin of the myocytes (P < 0.01, ANOVA). Mean action potential duration at 90 % repolarization (APD90) was 237 +/- 8 ms in subendocardial (n = 30 myocytes), 251 +/- 7 ms in midmyocardial (n = 30) and 204 +/- 7 ms in subepicardial myocytes (n = 36). L-type calcium current (ICa) density and background potassium current (IK1) density were similar in the three regions studied. Delayed rectifier current (IK) was measured as deactivating tail current, elicited on repolarization back to -45 mV after 2 s step depolarizations to test potentials ranging from -10 to +80 mV. Mean IK density (after a step to +80 mV) was larger in subepicardial myocytes (1.59 +/- 0.16 pA pF-1, n = 16) than in either subendocardial (1.16 +/- 0.12 pA pF-1, n = 17) or midmyocardial (1. 13 +/- 0.11 pA pF-1, n = 21) myocytes (P < 0.05, ANOVA). The La3+-insensitive current (IKs) elicited on repolarization back to -45 mV after a 250 ms step depolarization to +60 mV was similar in the three regions studied. The La3+-sensitive tail current, (IKr) was greater in subepicardial (0.50 +/- 0.04 pA pF-1, n = 11) than in subendocardial (0.25 +/- 0.05 pA pF-1, n = 9) or in midmyocardial myocytes (0.38 +/- 0.05 pA pF-1, n = 11, P < 0.05, ANOVA). The contribution of a Na+ background current to regional differences in APD was assessed by application of 0.1 microM tetrodotoxin (TTX). TTX-induced shortening of APD90 was greater in subendocardial myocytes (35.7 +/- 7.1 %, n = 11) than in midmyocardial (15.7 +/- 3. 8 %, n = 10) and subepicardial (20.2 +/- 4.3 %, n = 11) myocytes (P < 0.05, ANOVA). Regional differences in action potential characteristics between subendocardial, midmyocardial, and subepicardial myocytes isolated from guinea-pig left ventricle are attributable, at least in part, to differences in IK and Na+-dependent currents.
研究了从豚鼠心脏左心室游离壁分离出的心内膜下、心肌中层和心外膜下心肌细胞动作电位特征和膜电流的区域差异。动作电位持续时间（APD）取决于心肌细胞的起源区域（P<0.01，方差分析）。心内膜下心肌细胞（n = 30个心肌细胞）在90%复极化时的平均动作电位持续时间（APD90）为237±8毫秒，心肌中层（n = 30）为251±7毫秒，心外膜下心肌细胞（n = 36）为204±7毫秒。在所研究的三个区域中，L型钙电流（ICa）密度和背景钾电流（IK1）密度相似。延迟整流电流（IK）作为失活尾电流进行测量，在2秒的阶跃去极化至-10至+80 mV的测试电位后，复极化回到-45 mV时引发。心外膜下心肌细胞（1.59±0.16 pA pF-1，n = 16）中平均IK密度（在阶跃至+80 mV后）大于心内膜下（1.16±0.12 pA pF-1，n = 17）或心肌中层（1.13±0.11 pA pF-1，n = 21）心肌细胞（P<0.05，方差分析）。在250毫秒阶跃去极化至+60 mV后复极化回到-45 mV时引发的La3 +不敏感电流（IKs）在所研究的三个区域中相似。La3 +敏感尾电流（IKr）在心外膜下（0.50±0.04 pA pF-1，n = 11）大于心内膜下（0.25±0.05 pA pF-1，n = 9）或心肌中层心肌细胞（0.38±0.05 pA pF-1，n = 11，P<0.05，方差分析）。通过应用0.1微摩尔河豚毒素（TTX）评估Na +背景电流对APD区域差异的贡献。TTX诱导的APD90缩短在心内膜下心肌细胞（35.7±7.1%，n = 11）中大于心肌中层（15.7±3.8%，n = 10）和心外膜下（20.2±4.3%，n = 11）心肌细胞（P<0.05，方差分析）。从豚鼠左心室分离的心内膜下、心肌中层和心外膜下心肌细胞之间动作电位特征的区域差异至少部分归因于IK和Na +依赖性电流的差异。
