Kodama I, Toyama J, Yamada K
Jpn Circ J. 1981 Apr;45(4):410-8. doi: 10.1253/jcj.45.410.
Effects of high frequency (HF) stimulation on membrane potential were examined in ventricular muscle and Purkinje fibers, which were isolated from canine and rabbit hearts, by using microelectrode techniques. When the stimulating frequency of preparations was increased abruptly from basic frequency (BF, 0-30/min) to high frequency (HF, 60-150/min), the maximum diastolic potential (MDP) of both ventricular muscle and Purkinje fibers decreased with each beat and reached a minimal value (initial depolarization). Then, MDP gradually increased beyond the steady state level at BF (hyperpolarization). On returning the stimulating frequency from HF to BF, a further terminal hyperpolarization ensued, and finally MDP decayed back (both depolarization and hyperpolarization) was apparently greater in ventricular muscle than in Purkinje fibers. A significant increase of threshold current for excitation and a slight increase of membrane input resistance were also observed at the hyperpolarized period after HF stimulation. Lowering the temperature of the perfusate from 37 degrees C (control) to 31 degrees C or 26 degrees C led to an augmentation of initial depolarization and also a decrease in the intensity of ensuing hyperpolarization. The decay time of the hyperpolarization after HF stimulation was much prolonged. In the presence of ouabain, HF stimulation caused a monotonic decline in MDP and no hyperpolarization was recorded during and after HF stimulation. These results suggest that an active ion transport through the sodium pump contributes significantly to the electrical properties of ventricular muscle as well as the Purkinje fibers when the firing rate of the fibers is abruptly changed.
采用微电极技术，研究了高频（HF）刺激对从犬和兔心脏分离出的心室肌和浦肯野纤维膜电位的影响。当标本的刺激频率从基础频率（BF，0 - 30次/分钟）突然增加到高频（HF，60 - 150次/分钟）时，心室肌和浦肯野纤维的最大舒张电位（MDP）随每次搏动而降低，并达到最小值（初始去极化）。然后，MDP逐渐增加，超过BF时的稳态水平（超极化）。当刺激频率从HF恢复到BF时，会出现进一步的终末超极化，最终MDP衰减恢复（去极化和超极化），心室肌的变化明显大于浦肯野纤维。在HF刺激后的超极化期，还观察到兴奋阈值电流显著增加，膜输入电阻略有增加。将灌流液温度从37℃（对照）降至31℃或26℃，会导致初始去极化增强，随后超极化强度降低。HF刺激后超极化的衰减时间大大延长。在哇巴因存在的情况下，HF刺激导致MDP单调下降，在HF刺激期间和之后未记录到超极化。这些结果表明，当纤维的放电频率突然改变时，通过钠泵的主动离子转运对心室肌和浦肯野纤维的电特性有显著贡献。
