Effect of subthreshold voltage-dependent conductances on the transfer function of branched excitable cells and the conduction of synaptic potentials.
Effect of subthreshold voltage-dependent conductances on the transfer function of branched excitable cells and the conduction of synaptic potentials.
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DOI：
10.1152/jn.1988.59.3.706
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发表时间：
1988-03
影响因子：
2.5
通讯作者：
K. Yoshii;L. Moore;B. Christensen
中科院分区：
文献类型：
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作者：
K. Yoshii;L. Moore;B. Christensen
1.从培养的NG-108细胞的复点阻抗和传递函数确定脉冲响应函数，以模拟响应于发射物释放的突触电位的传播。一般来说，突触电流的流动具有比正常膜时间常数短得多的持续时间，从而使得使用脉冲响应函数对突触事件有用的近似。2.在钾电导激活过程中观察到的共振反映在脉冲响应函数中，作为一个明显的阻尼振荡。从点阻抗和传递函数计算的脉冲响应函数的比较显示出类似的结果，在生长锥的电流注入。3.除了主要由于激活外向电流的电导的电压依赖性电导对传递和脉冲响应函数的谐振效应之外，在稳态负电导的激活期间测量传递函数。在这些条件下，相位函数接近180度，表明电压响应与电流异相。4.在稳定状态下，负电导的影响是代数地增加到正电导，并且通常减小绝对电导，除非存在净负电流。降低的电导增强了脉冲响应和DC空间常数，从而导致慢电位的更好传播。这种效应可以被看作是电紧张长度L的减小，具有中间去极化。在大的去极化的K电导的稳态激活一般占主导地位，并导致大大增加的电紧张长度。5.净电导和相关的动力学都在突触电流期间形成电位变化中起作用。如果存在净负稳态电导，这一点尤其重要。在这些条件下，脉冲响应函数有令人惊讶的降低。6.因此，在电压依赖性负电导的亚阈值激活期间，可观察到的突触电位将是由于阻抗的明显增加（正电导和负电导与净正电导的代数求和）引起的大电位响应，或者是由于净负电导引起的相位抵消引起的最小响应。由于大的突触驱动，后一种情况可能存在于突触逆转电位附近，并且在实验中表现为一种抑制形式。（400字处删节）
1. Impulse response functions were determined from complex point impedance and transfer functions from cultured NG-108 cells to simulate the propagation of a synaptic potential in response to the release of transmitter. In general, the flow of synaptic current has a much shorter duration than the normal membrane time constant, thereby making the use of impulse response functions useful approximations to synaptic events. 2. The resonance observed during the activation of the potassium conductance was reflected in the impulse response function as a pronounced damped oscillation. A comparison of the impulse response functions calculated from point impedance and transfer functions showed similar results for current injections in the growth cone. 3. In addition to the resonance effects of the voltage-dependent conductances on transfer and impulse response functions due principally to the activation of conductances for outward currents, transfer functions were measured during the activation of a steady-state negative conductance. Under these conditions the phase function approaches 180 degrees, indicating that the voltage response is out of phase with the current. 4. In the steady state, the effect of a negative conductance is to algebraically add to the positive conductances and generally decrease the absolute conductance unless there is a net negative current. The decreased conductance enhances the impulse response and the DC space constant, thus leading to a better propagation of slow potentials. This effect can be seen as a decrease in the electrotonic length, L, with intermediate depolarizations. At large depolarizations the steady-state activation of the K conductance generally dominates and leads to a greatly increased electrotonic length. 5. Both the net conductances and the associated kinetics play a role in shaping the potential changes during a synaptic current. This is especially critical if there is a net negative steady-state conductance. Under these conditions there is a surprising reduction in the impulse response function. 6. Thus, during a subthreshold activation of the voltage-dependent negative conductances, the observable synaptic potentials would be either large potential responses due to an apparent increase in the impedance (algebraic summation of positive and negative conductances with a net positive conductance) or a minimal response because of the phasic cancellation due to a net negative conductance. The latter condition could exist near the synaptic reversal potential due to a large synaptic drive and would appear experimentally as a form of inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)