Casis O, Iriarte M, Gallego M, Sánchez-Chapula J A
University of the Basque Country, School of Pharmacy, Department of Physiology, Bilbao, Spain.
Life Sci. 1998;63(5):391-400. doi: 10.1016/s0024-3205(98)00287-2.
The objective of the present work is to study the ionic mechanisms for the regional differences in action potential duration in rat ventricle. This regional diversity has been related to differences in the regional distribution of some potassium currents in several species. Single cells were obtained by enzymatic dispersion of tissue segments from rat ventricular muscle. Whole cell voltage-clamp methods were used to identify the K+ currents involved in action potential repolarisation in the different regions. 4-Aminopiridine, TEA and voltage protocols were used to isolate the following potassium currents: transient outward, Ito, delayed rectifier, Ik, and sustained current, Iss. In the present work, we have studied the distribution of these three repolarising currents, and that of the inward rectifier, Ikl, in the free wall of the right ventricle, the subepicardium of the apex of the left ventricle and in the subendocardium of the base of the left ventricle. Action potential duration was longer in the left than in the right ventricle, and in the former it was longer in the subendocardium of the base than in the subepicardium of the apex. The main difference was in the phase 1, suggesting the implication of Ito. This was confirmed with voltage-clamp experiments. In conclusion, this work shows that Ito current density is higher in the regions with the shorter action potential, whereas there are no differences in the regional distribution of Ik, Iss or Ikl.
本研究的目的是探讨大鼠心室动作电位时程区域差异的离子机制。这种区域多样性与几种物种中某些钾电流区域分布的差异有关。通过酶解大鼠心室肌组织片段获得单细胞。采用全细胞电压钳技术来确定不同区域动作电位复极化过程中涉及的钾电流。使用4-氨基吡啶、四乙铵和电压方案来分离以下钾电流：瞬时外向电流（Ito）、延迟整流电流（Ik）和持续电流（Iss）。在本研究中，我们研究了这三种复极化电流以及内向整流电流（Ikl）在右心室游离壁、左心室心尖部的心外膜下和左心室基部的心内膜下的分布情况。左心室的动作电位时程比右心室长，并且在左心室中，基部的心内膜下比心尖部的心外膜下的动作电位时程更长。主要差异在第1期，提示Ito参与其中。电压钳实验证实了这一点。总之，本研究表明，动作电位时程较短的区域中Ito电流密度较高，而Ik、Iss或Ikl的区域分布没有差异。
