Schouten V J
J Mol Cell Cardiol. 1986 Oct;18(10):1033-45. doi: 10.1016/s0022-2828(86)80291-7.
Action potential duration at 50% of the amplitude (APD50) and peak force of isometric contractions were recorded from right ventricular trabeculae of rat heart at 26 degrees C. When the preparation was in the steady state at 0.2 Hz, a varied test interval was interposed. The premature contraction after a test interval of 0.25 s showed reduced force and increased APD50. Gradual prolongation of the interval from 0.25 to 80 s led to a gradual increase of force and shortening of APD50. At longer intervals force decreased and APD50 increased. This gave a negative APD50-force correlation. In the presence of the Ca2+ antagonists nifedipine or Mn2+, force was reduced to about 70%. APD50 was shortened to about 50% and was almost independent of the test interval. The slope of the negative APD50-force relationship was only 20% of that under control conditions. It is concluded that the inward Ca2+ current, isi, is a prerequisite for the interval-dependent changes in APD50 and for the negative APD50-force relationship. A reduction of the stimulation frequency from 0.2 to 0.003 Hz resulted in a gradual reduction of force and prolongation of APD50. Both force and APD50 were then almost independent of interposed test intervals. In low [Na+], at 0.2 Hz, force was almost maximal and APD50 was short at all test intervals. Thus, throughout these two interventions all changes in force were associated with opposite changes in APD50. The causal factor underlying the negative APD50-force relationship is probably an intracellular release of Ca2+ which activates the contractile filaments and inactivates isi.
在26摄氏度下，记录大鼠心脏右心室小梁的动作电位持续时间（50%振幅时，APD50）和等长收缩的峰值力。当标本在0.2 Hz频率下处于稳态时，插入不同的测试间期。0.25 s测试间期后的早搏显示力降低，APD50增加。将间期从0.25 s逐渐延长至80 s导致力逐渐增加，APD50缩短。在更长的间期时，力降低，APD50增加。这呈现出APD50与力的负相关关系。在存在钙拮抗剂硝苯地平或锰离子的情况下，力降低至约70%。APD50缩短至约50%，且几乎与测试间期无关。APD50与力的负相关关系的斜率仅为对照条件下的20%。结论是内向钙电流isi是APD50间期依赖性变化以及APD50与力的负相关关系的前提条件。刺激频率从0.2 Hz降至0.003 Hz导致力逐渐降低，APD50延长。此时力和APD50几乎都与插入的测试间期无关。在低钠浓度下，0.2 Hz时，在所有测试间期力几乎最大，APD50较短。因此，在这两种干预过程中，力的所有变化都与APD50的相反变化相关。APD50与力的负相关关系的潜在因果因素可能是细胞内钙释放，它激活收缩细丝并使isi失活。
