Benditt D G, Scheinman M M, Snow T R, Strauss H C
Can J Physiol Pharmacol. 1982 Dec;60(12):1519-25. doi: 10.1139/y82-224.
Using standard microelectrode techniques, we evaluated effects of diminished oxygen tension on the magnitude and time course of frequency dependent changes in maximum diastolic transmembrane potential (MDP) and on alteration of action potential duration (APD) in feline Purkinje fibers. MDP was recorded continuously during a control period (cycle length (CL) = 1000 ms), during a 5-min period of rapid drive (CL = 400 ms) and following return to pacing CL = 1000 ms. Rapid drive resulted in hyperpolarization of MDP from control value; and after return to pacing CL = 1000 ms. MDP gradually depolarized, eventually attaining a steady state value within +/- 0.5 mV of the control value. The difference between hyperpolarized MDP value and final steady-state value was designated VH, and the decline of MDP towards steady-state value approximated an exponential function (time constant = tau VH). Exposure to reduced PO2 (75 +/- 2.1 mmHg vs. control 473 +/- 39.1 mmHg) (1 mmHg = 133.322 Pa) resulted in reduction in the magnitude of VH (6.2 +/- 3.43 mV vs. 7.8 +/- 2.73 mV, mean +/- SD, p less than 0.005) and shortening of APD within 0-24 min, while measurable prolongation of tau VH (75 +/- 18.5 vs. 54 +/- 9.0 s, p less than 0.005) began at 25-49 min following onset of reduced PO2. These observations suggest that rate-related changes of MDP in cardiac tissues are oxygen dependent, and they support previously reported analagous observations in nerve which suggested that frequency dependent potential changes may in part reflect alterations of electrogenic Na-K pump activity.
我们运用标准微电极技术，评估了氧分压降低对猫浦肯野纤维最大舒张跨膜电位（MDP）频率依赖性变化的幅度及时程以及动作电位时程（APD）改变的影响。在对照期（周期长度（CL）=1000毫秒）、快速驱动5分钟期（CL = 400毫秒）以及恢复到起搏CL = 1000毫秒后，持续记录MDP。快速驱动导致MDP相对于对照值发生超极化；恢复到起搏CL = 1000毫秒后，MDP逐渐去极化，最终达到对照值±0.5毫伏内的稳态值。超极化MDP值与最终稳态值之间的差值被定义为VH，MDP向稳态值的下降近似指数函数（时间常数=τVH）。暴露于降低的PO2（75±2.1毫米汞柱，对照为473±39.1毫米汞柱）（1毫米汞柱=133.322帕斯卡）导致VH幅度减小（6.2±3.43毫伏对7.8±2.73毫伏，均值±标准差，p<0.005），并在0 - 24分钟内使APD缩短，而τVH的可测量延长（75±18.5对54±9.0秒，p<0.005）在PO2降低开始后25 - 49分钟开始。这些观察结果表明，心脏组织中与速率相关的MDP变化是氧依赖性的，并且支持先前在神经中报道的类似观察结果，即频率依赖性电位变化可能部分反映了生电钠钾泵活性的改变。
