小鼠心室肌细胞外向电流的特征分析

CHARACTERIZAIZATION OF OUTWARD CURREN IN MOUSE VENTRICULAR MYOCYTES

用全细胞膜片箝技术研究了小鼠心室肌细胞去极化激活的非钙依赖性外向电流的特征。短时去极化至－５０ｍＶ以上电位可引发快速上升的外向钾电流，之后缓慢衰减至一平台。在改变保持电位时，该峰电流与平台电流的比值也发生改变，并测得两者翻转电位分别为－６４．３±３．９和－５３．３±２．９ｍＶ。外向电流的衰减过程可用双指数方式很好拟合，而在５００ｍｓ预脉冲刺激后再经去极化刺激的电流时程适合单指数方式。结果提示：小鼠心室肌细胞的外向电流包括两种失活成分（Ｉｋｆ，和Ｉｋｓ），它们对４－氨基吡啶具有相似的敏感性。Ｉｋｆ的稳态失活在测试电位范围内（－８０－＋３０ｍＶ）均不完全，这可能与小鼠心肌动作电位时程很短有关联。

Depolarization -activated,calcium-independentoutward currents(Iout )in enzymat ically dispersed mouse ventricular myocytes were characterized by whole-cell recording technique. During brief depolarizations to potentials postive to- 50 mV, outward K+currents in these cells rise rapidly to a Peak followed by a slower decay to an apparentplateau.The relative peak to plateau amplitudes in a single cell varied as a function of the holding potential (HP) from which the currents were evoked. Reversal potentials for the peak and plateau components were - 64. 3±3. 9 mV and - 53. 3±2. 9 mV,respectively (uncorrected for junction potentials). The outward current decay. is well described by double exponential fits whereas the time course of Peak Iout decay following a 500 ms prepulse is best fitted by single exponential function, indicating the presenceof two distinct components, Ikf and IKs, of the outward currents in mouse ventricular cells. Application of 4-AP were accompanied by a marked attenuation of Peak Iout andplateau Iout, indicating that both IKf and IKs display similar sensitivities to 4-AP. The steady state inactivation of Ikf is found incomplete within the test potential range (80-+ 30 mV) owing probably to the fact that the APD of mouse myocardium is too short.