Contribution of single-channel properties to the time course and amplitude variance of quantal glycine currents recorded in rat motoneurons.
Contribution of single-channel properties to the time course and amplitude variance of quantal glycine currents recorded in rat motoneurons.
复制标题
单通道特性对大鼠运动神经元中记录的量子甘氨酸电流的时间过程和幅度方差的贡献。
DOI：
10.1152/jn.1999.81.4.1608
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发表时间：
1999
期刊：
影响因子：
--
通讯作者：
Berger,AJ
中科院分区：
文献类型：
--
作者：
Singer,JH;Berger,AJ
单通道特性对大鼠运动神经元甘氨酸量子电流时程和幅度变化的影响。 在体外脑干切片制备中，舌下神经运动神经元（HM）中记录的自发性甘氨酸能微型抑制性突触后电流（mIPSC）的幅度在出生后的前3周内增加，从新生儿（P0-3）的42 ± 6 pA增加到幼年（P11-18）HM的77 ± 11 pA。此外，mIPSC振幅分布高度可变：新生儿CV 0.68 ± 0.05（平均值± SE），青少年CV 0.83 ± 0.06。我们希望确定甘氨酸受体（GlyR）通道特性对量子振幅变化以及mIPSC的振幅变异性和时程的贡献。为了确定出生后GlyR通道电导的增加是否解释了量子振幅的出生后变化，通过mIPSC的非平稳方差分析确定突触GlyR通道的电导。在新生儿中为48 ± 8 pS，在幼年HM中为46 ± 10 pS，表明mIPSC振幅的发育变化不是由出生后GlyR通道电导的改变引起的。接下来，我们确定了从HM中切除的外向补丁中GlyR通道的开放概率（Popen），以估计随机通道行为对量子幅度变化的贡献。甘氨酸（ImM）的短暂（Ims）脉冲引起非常类似于mIPSC的贴片电流。用非平稳方差分析计算出GlyR通道的Popen为0.70（新生儿为0.66 ± 0.09，青少年为0.72 ± 0.05）。贴片电流的衰减率引起的短暂应用饱和浓度的甘氨酸（10 mM）出生后增加，模仿先前记录的变化mIPSC的时间过程。使用甘氨酸（10 mM）的成对脉冲来确定快速GlyR通道脱敏是否有助于贴片电流时程或量子振幅变异性。因为我们没有观察到任何快速脱敏的补丁电流，我们认为，快速脱敏的GlyRs的基础都没有现象。从我们对甘氨酸能斑电流和mIPSC的分析中，我们得出三个结论。首先，通道失活是甘氨酸能mIPSC时程的主要决定因素，并且通道失活速率的出生后变化解释了观察到的mIPSC衰减速率的发育变化。第二，因为GlyR通道Popenis高，突触之间的受体数量的差异，而不是随机通道行为可能是大多数的量子变异性的基础，在整个出生后的发展甘氨酸能突触。我们估计，在突触中可用的GlyR的数量在新生神经元中平均为27个，在幼年神经元中平均为39个。第三，在每个突触处计算的GlyR数量的这种变化可以解释出生后mIPSC振幅的增加。
Contribution of single-channel properties to the time course and amplitude variance of quantal glycine currents recorded in rat motoneurons. The amplitude of spontaneous, glycinergic miniature inhibitory postsynaptic currents (mIPSCs) recorded in hypoglossal motoneurons (HMs) in an in vitro brain stem slice preparation increased over the first 3 postnatal weeks, from 42 ± 6 pA in neonate (P0–3) to 77 ± 11 pA in juvenile (P11–18) HMs. Additionally, mIPSC amplitude distributions were highly variable: CV 0.68 ± 0.05 (means ± SE) for neonates and 0.83 ± 0.06 for juveniles. We wished to ascertain the contribution of glycine receptor (GlyR)-channel properties to this change in quantal amplitude and to the amplitude variability and time course of mIPSCs. To determine whether a postnatal increase in GlyR-channel conductance accounted for the postnatal change in quantal amplitude, the conductance of synaptic GlyR channels was determined by nonstationary variance analysis of mIPSCs. It was 48 ± 8 pS in neonate and 46 ± 10 pS in juvenile HMs, suggesting that developmental changes in mIPSC amplitude do not result from a postnatal alteration of GlyR-channel conductance. Next we determined the open probability (Popen) of GlyR channels in outside-out patches excised from HMs to estimate the contribution of stochastic channel behavior to quantal amplitude variability. Brief (1 ms) pulses of glycine (1 mM) elicited patch currents that closely resembled mIPSCs. The GlyR channels’Popen, calculated by nonstationary variance analysis of these currents, was ∼0.70 (0.66 ± 0.09 in neonates and 0.72 ± 0.05 in juveniles). The decay rate of patch currents elicited by brief application of saturating concentrations of glycine (10 mM) increased postnatally, mimicking previously documented changes in mIPSC time course. Paired pulses of glycine (10 mM) were used to determine if rapid GlyR-channel desensitization contributed to either patch current time course or quantal amplitude variability. Because we did not observe any fast desensitization of patch currents, we believe that fast desensitization of GlyRs underlies neither phenomenon. From our analysis of glycinergic patch currents and mIPSCs, we draw three conclusions. First, channel deactivation is the primary determinant of glycinergic mIPSC time course, and postnatal changes in channel deactivation rate account for observed developmental changes in mIPSC decay rate. Second, because GlyR-channelPopenis high, differences in receptor number between synapses rather than stochastic channel behavior are likely to underlie the majority of quantal variability seen at glycinergic synapses throughout postnatal development. We estimate the number of GlyRs available at a synapse to be on average 27 in neonate neurons and 39 in juvenile neurons. Third, this change in the calculated number of GlyRs at each synapse may account for the postnatal increase in mIPSC amplitude.