Clay J R, Shrier A
Ion Channel Biophysics Unit, Division of Intramural Research, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
J Membr Biol. 2002 Jun 1;187(3):213-23. doi: 10.1007/s00232-001-0165-3.
Raising the intracellular pH (pHi) above 7.7 in intracellularly perfused squid giant axons causes spontaneous firing of action potentials. The firing frequency ranged from 20 Hz at 0 degrees C to 200 Hz at 23 degrees C. Above 23 degrees C, the axons were quiescent. They were bistable for 13 <T <23 degrees C. That is, they were either quiescent or spontaneously firing. Below 13 degrees C, spontaneous firing was the only stable element. The primary effects of changes in temperature on the underlying ionic currents were on gating of the delayed rectifier potassium channel IK, and the sodium ion channel INa. The kinetics of IK had a Q10 of 3.63. The effect of T on INa was more complicated in that the peak INa amplitude increased with T, as demonstrated in earlier reports. This effect, as well as the changes in INa kinetics produced by changes in T, were mimicked in the context of a model of INa gating in which activation and inactivations are coupled. Electrical activity was simulated in a model of the action potential with appropriate temperature-dependent modifications for INa and IK. The model predicts a change from monostability (spontaneous firing) at relatively low temperatures to bistability (quiescence and spontaneous firing) as the temperature is raised, followed by change back to monostability (quiescence) as the temperature is further increased, which is consistent with the experimental results.
在细胞内灌流的枪乌贼巨大轴突中，将细胞内pH（pHi）提高到7.7以上会引发动作电位的自发放电。放电频率范围为0℃时20Hz至23℃时200Hz。在23℃以上，轴突处于静止状态。在13℃<T<23℃时它们是双稳态的。也就是说，它们要么静止，要么自发放电。在13℃以下，自发放电是唯一的稳定状态。温度变化对潜在离子电流的主要影响在于延迟整流钾通道IK和钠离子通道INa的门控。IK的动力学Q10为3.63。T对INa的影响更为复杂，因为如早期报告所示，INa峰值幅度随T升高。在激活和失活相互耦合的INa门控模型中，模拟了这种效应以及由T变化产生的INa动力学变化。在动作电位模型中模拟电活动，并对INa和IK进行适当的温度依赖性修改。该模型预测，随着温度升高，会从相对低温下的单稳态（自发放电）转变为双稳态（静止和自发放电），随后随着温度进一步升高又变回单稳态（静止），这与实验结果一致。
