The kinetic properties of wild-type rat brain IIa sodium channels in excised macropatches were studied using step depolarizations and ramp depolarizations to imitate the slow settling-time of voltage in two-electrode voltage clamp. Ramp depolarizations longer than 1 ms produce an increasing suppression of peak sodium current (I[Na]). Two rates of inactivation can be seen in macroscopic sodium current records from excised patches following both step and ramp depolarizations. During slow ramp depolarizations, reduction in peak I[Na] is associated with selective loss of the fastest rate of test-pulse inactivation. This change can be interpreted as resulting from inactivation of a separate sub-population of 'fast mode' channels. The slow rate of test-pulse inactivation is relatively unaffected by changing ramp durations. These results are sufficient to explain the typically slow inactivation kinetics seen in two-electrode voltage clamp recordings of sodium channels in Xenopus oocytes. Thus, the kinetics of sodium channels expressed in Xenopus oocytes are not readily characterizable by two-electrode clamp because of the large membrane capacitance and resulting slow clamp settling time which artifactually selects for slow mode channels.

译文

使用逐步去极化和斜坡去极化来模拟两电极电压钳位中电压的缓慢建立时间,研究了切除的大斑块中野生型大鼠脑IIa钠通道的动力学特性。长于1 ms的斜坡去极化会增加对峰值钠电流 (I[Na]) 的抑制。在阶跃和斜坡去极化之后,从切除的斑块的宏观钠电流记录中可以看到两种失活速率。在缓慢的斜坡去极化过程中,峰值I[Na] 的降低与最快的测试脉冲失活速率的选择性损失有关。此更改可以解释为由于 “快速模式” 通道的单独子种群的失活而导致。测试脉冲失活的缓慢速度相对不受斜坡持续时间变化的影响。这些结果足以解释非洲爪蟾卵母细胞中钠通道的两电极电压钳制记录中看到的典型的缓慢失活动力学。因此,非洲爪蟾卵母细胞中表达的钠通道的动力学不容易通过两电极钳来表征,因为膜电容大,并且会导致人为选择慢模式通道而产生的慢钳建立时间。

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