Ladilov Y V, Siegmund B, Balser C, Piper H M
Physiologisches Institut, Justus-Liebig-Universität, Giessen, Germany.
Circ Res. 1997 Jan;80(1):69-75. doi: 10.1161/01.res.80.1.69.
The hypothesis that rat cardiomyocytes become susceptible to hypercontracture after anoxia/reoxygenation was investigated. The cells were gradually overloaded with Ca2+ after different periods of simulated ischemia (substrate-free anoxia, medium at pH 6.4) followed by 20 minutes of reoxygenation. The cytosolic Ca2+ concentration (measured with fura 2) at which the cells developed maximal hypercontracture (Camax) was used as an index for their susceptibility to hypercontracture (SH). SH was increased in cardiomyocytes after prolonged periods of simulated ischemia; ie, these cells developed hypercontracture at significantly lower cytosolic Ca2+ levels than did normoxic cells (Camax, 0.80 +/- 0.05 mumol/L versus 1.27 +/- 0.05 mumol/L; P < .01). To find the possible cause of increased SH, the influence of Ca2+ overload, acidosis, and protein dephosphorylation were studied. Prevention of cytosolic Ca2+ overload in anoxic cardiomyocytes or imitation of ischemic acidosis in normoxic cells did not influence Camax. In contrast, use of 10 mumol/L cantharidin (inhibitor of protein phosphatases 1 and 2A) during anoxic superfusion prevented the reduction of Camax. Furthermore, treatment of normoxic cardiomyocytes with 20 mmol/L of the chemical phosphatase 2,3-butanedione monoxime reduced Camax. Therefore, prolonged simulated ischemia increases susceptibility of cardio-myocytes to hypercontracture. This seems to be due to protein dephosphorylation.
研究了大鼠心肌细胞在缺氧/复氧后易发生超收缩的假说。在不同时间段的模拟缺血（无底物缺氧，pH 6.4的培养基）后，细胞逐渐被Ca2+超载，随后复氧20分钟。将细胞出现最大超收缩时的胞质Ca2+浓度（用fura 2测量）（Camax）用作其对超收缩敏感性（SH）的指标。长时间模拟缺血后，心肌细胞的SH增加；即，这些细胞在明显低于常氧细胞的胞质Ca2+水平时就出现超收缩（Camax，0.80±0.05 μmol/L对1.27±0.05 μmol/L；P<.01）。为了找出SH增加的可能原因，研究了Ca2+超载、酸中毒和蛋白质去磷酸化的影响。防止缺氧心肌细胞的胞质Ca2+超载或在常氧细胞中模拟缺血酸中毒对Camax没有影响。相反，在缺氧灌注期间使用10 μmol/L的斑蝥素（蛋白磷酸酶1和2A的抑制剂）可防止Camax降低。此外，用20 mmol/L的化学磷酸酶2,3-丁二酮单肟处理常氧心肌细胞可降低Camax。因此，长时间的模拟缺血增加了心肌细胞对超收缩的敏感性。这似乎是由于蛋白质去磷酸化。
