质子诱导鸡背根神经节细胞中钙通道的转变。
Proton-induced transformation of calcium channel in chick dorsal root ganglion cells.
作者信息
Konnerth A, Lux H D, Morad M
机构信息
Department of Neurophysiology, Max-Planck-Institute for Psychiatry, Planegg, F.R.G.
出版信息
J Physiol. 1987 May;386:603-33. doi: 10.1113/jphysiol.1987.sp016553.
- In dissociated and cultured 2-5-day-old chick dorsal root ganglion cells, a large transient inward current could be activated in response to a 'step' increase in [H+]o. 2. Using the single-electrode patch clamp technique in its whole-cell configuration, the proton-induced current was graded with [H+]o and relaxed in 1-2 s. 3. The pH dependence of the current was sigmoid with activation occurring at around pH 7.0 (at[Ca2+]o = 1 mM) and a maximum at pH 6.0-5.5. 4. Small increases of [H+]o, which by themselves failed to activate a significant amount of current, inactivated the proton-induced current. The half-maximum of inactivation occurred at pH 7.11 at [Ca2+]o = 5 mM, but this changed to pH 7.32 at [Ca2+]o = 1 mM. 5. The proton-induced inward current reversed direction at the Na+ equilibrium potential and was suppressed in the absence of [Na+]o. Measurement of the reversal potential at different [Na+]o and/or [Na+]i showed a linear relation with a slope of 58 mV/decade as predicted from the Nernst equation. Thus, proton-induced current was carried by Na+ and was abbreviated as INa(H). 6. The membrane conductance associated with INa(H) showed no voltage dependence, but did change in parallel with the activation of the current. The membrane conductance increased by a factor of 10-20-fold at the peak of the inward current. 7. INa(H) was blocked by organic and inorganic Ca2+ channel blockers (diltiazem, Cd2+ and Ni2+), but was unaffected by high concentrations of tetrodotoxin (TTX) or steady-state increases of the [Ca2+]i to 10(-4) M or the [H+]i to 10(-6) M. 8. In outside-out membrane patches, the single channel associated with the proton-induced current opened in bursts, with long pauses. The mean open time during the bursts was 1.26 ms and the channel had a conductance of 20-25 pS at -80 mV (120 mM [Na2+]o, 20 mM [Na2+]i). 9. Measurement of the voltage-gated Ca2+ current using short (30-50 ms) depolarizing pulses to zero showed that the Ca2+ current (ICa) but not the fast Na+ current (INa) was completely suppressed during the time course of activation of INa(H). 10. INa(H) was completely blocked by high (35-40 mM) [Ca2+]o. 11. Simultaneous elevation of [H+]o and [Ca2+]o failed to activate INa(H) but enhanced the voltage-gated Ca2+ channel. 12. Our data show that the proton-induced current is carried by Na+ flowing through a transformed Ca2+ channel.(ABSTRACT TRUNCATED AT 400 WORDS)
在解离并培养的2至5日龄鸡背根神经节细胞中，细胞外[H⁺]的“阶跃”增加可激活一个大的瞬时内向电流。
使用全细胞模式的单电极膜片钳技术，质子诱导电流随细胞外[H⁺]浓度分级变化，并在1至2秒内衰减。
电流的pH依赖性呈S形，在pH约7.0时激活（细胞外[Ca²⁺]=1 mM），在pH 6.0 - 5.5时达到最大值。
细胞外[H⁺]的小幅增加本身未能激活大量电流，但却使质子诱导电流失活。失活的半数最大值在细胞外[Ca²⁺]=5 mM时出现在pH 7.11，但在细胞外[Ca²⁺]=1 mM时变为pH 7.32。
质子诱导的内向电流在Na⁺平衡电位处反转方向，且在无细胞外[Na⁺]时受到抑制。在不同的细胞外[Na⁺]和/或细胞内[Na⁺]条件下测量反转电位，显示出与能斯特方程预测相符的线性关系，斜率为58 mV/十倍浓度变化。因此，质子诱导电流由Na⁺携带，简称为INa(H)。
与INa(H)相关的膜电导不显示电压依赖性，但随电流激活而平行变化。内向电流峰值时，膜电导增加10至20倍。
INa(H)被有机和无机Ca²⁺通道阻滞剂（地尔硫卓、Cd²⁺和Ni²⁺）阻断，但不受高浓度河豚毒素（TTX）影响，也不受细胞内[Ca²⁺]稳态增加至10⁻⁴ M或细胞内[H⁺]增加至10⁻⁶ M的影响。
在外侧向外膜片上，与质子诱导电流相关的单通道呈爆发式开放，有长时间的间断。爆发期间的平均开放时间为1.26毫秒，在-80 mV（细胞外[Na⁺]=120 mM，细胞内[Na⁺]=20 mM）时通道电导为20至25 pS。
使用短（30至50毫秒）去极化脉冲至零电位测量电压门控Ca²⁺电流，结果表明在INa(H)激活过程中，Ca²⁺电流（ICa）而非快速Na⁺电流（INa）被完全抑制。
高（35至40 mM）细胞外[Ca²⁺]可完全阻断INa(H)。
细胞外[H⁺]和细胞外[Ca²⁺]同时升高未能激活INa(H)，但增强了电压门控Ca²⁺通道。
我们的数据表明，质子诱导电流由通过转化的Ca²⁺通道流动的Na⁺携带。（摘要截选至400字）
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