Keung E C, Toll L, Ellis M, Jensen R A
Cardiology Section, Veterans Affairs Medical Center, San Francisco, CA 94121.
J Clin Invest. 1991 Jun;87(6):2108-13. doi: 10.1172/JCI115241.
Doxorubicin (DXR) is an effective antitumor agent in a wide spectrum of neoplasms. Chronic treatment is associated with cardiomyopathy and characteristic myocardial ultrastructural changes, which include swelling of the t tubules. Accordingly, we investigated excitation-contraction coupling in cardiomyopathic rat heart resulting from chronic DXR treatment. Using the whole-cell patch clamp technique, we studied the L-type calcium channel in single cells enzymatically isolated from normal (CTRL) and DXR rat hearts. Despite similar cell dimensions, the total membrane capacitance was significantly smaller in the DXR cells (138 +/- 9 pF) than in the CTRL cells (169 +/- 11 pF) (mean +/- SEM, n = 9, P less than 0.05). The mean current and the current density-voltage relationships of the CTRL and the DXR cells were significantly different (n = 9, P less than 0.001) with the maximal peak L-type calcium current (ICa) density increased from 6.4 +/- 0.9 in CTRL cells to 10.5 +/- 2.4 microA/cm2 in the DXR cells (P less than 0.05). There was no shift either in the current-voltage relationship or the steady-state inactivation curve in the two cell groups. However, the fast time constant of inactivation was increased at a membrane voltage of -10 to 10 mV. Calcium channel antagonist equilibrium binding assays using [3H]-PN200-110 revealed no difference in the maximal receptor binding capacity (CTRL, 194 +/- 27 and DXR 211 +/- 24 fmol/mg protein; P greater than 0.05, n = 6) and in receptor affinity (CTRL, 0.15 +/- 0.05 and DXR 0.13 +/- 0.03 nM; P less than 0.05). These data suggest that a decrease in effective capacitance might be associated with t-tubular damage. Despite this decrease, ICa was increased in the DXR cells. Such an increase may result from an alteration in the properties of the calcium channels and/or recruitment of "hibernating" channels in the remaining surface and t-tubular membranes.
阿霉素（DXR）是一种对多种肿瘤有效的抗肿瘤药物。长期治疗与心肌病以及特征性的心肌超微结构改变有关，这些改变包括横管肿胀。因此，我们研究了慢性DXR治疗导致的心肌病大鼠心脏中的兴奋-收缩偶联。使用全细胞膜片钳技术，我们研究了从正常（CTRL）和DXR大鼠心脏中酶解分离的单个细胞中的L型钙通道。尽管细胞尺寸相似，但DXR细胞（138±9 pF）的总膜电容明显小于CTRL细胞（169±11 pF）（平均值±标准误，n = 9，P<0.05）。CTRL细胞和DXR细胞的平均电流以及电流密度-电压关系显著不同（n = 9，P<0.001），最大峰值L型钙电流（ICa）密度从CTRL细胞中的6.4±0.9增加到DXR细胞中的10.5±2.4 μA/cm2（P<0.05）。两组细胞的电流-电压关系或稳态失活曲线均无偏移。然而，在-10至10 mV的膜电压下，失活的快速时间常数增加。使用[3H]-PN200-110进行的钙通道拮抗剂平衡结合试验显示，最大受体结合能力（CTRL为194±27，DXR为211±24 fmol/mg蛋白质；P>0.05，n = 6）和受体亲和力（CTRL为0.15±0.05，DXR为0.13±0.03 nM；P<0.05）没有差异。这些数据表明有效电容的降低可能与横管损伤有关。尽管电容降低，但DXR细胞中的ICa增加。这种增加可能是由于钙通道特性的改变和/或剩余表面和横管膜中“休眠”通道的募集所致。
