Neumcke B, Stämpfli R
Pflugers Arch. 1984 Jun;401(2):125-31. doi: 10.1007/BF00583872.
The conductance gamma and the number of No of Na channels in the nodal membrane of frog nerve fibres were determined from ensemble average values of the Na current and the variance of Na current fluctuations. Replacement of extracellular Cl- by NO3- shifts the voltage dependencies of all Na gating parameters towards more negative voltages, reduces gamma by a factor of 0.84 and hardly changes the number No of channels not blocked by 8 nM TTX. Adding 0.1 mM LaCl3 to the extracellular solution shifts the voltage dependencies of all Na gating parameters towards more positive voltages, reduces gamma by a factor of 0.75 and hardly changes the number No of channels not blocked by 8 nM TTX. It is concluded that changes of the external surface potential induced by Cl-, NO3- replacement do not alter the local Na+ concentration in the outer mouth of the Na channel and hardly affect the TTX binding to toxin receptors. Surface potential changes by addition of LaCl3 also have no clear effect on TTX binding. The reduction of gamma in 0.1 mM LaCl3 is probably due to a direct interaction of La3+ with Na channels. Our results suggest a heterogeneous distribution of external fixed surface charges in the outer mouth of the Na channel, at the TTX binding site and near the Na channel gates.
通过钠电流的总体平均值和钠电流波动的方差，测定了蛙神经纤维节段膜中的电导γ和钠通道数量No。用NO3-取代细胞外Cl-会使所有钠门控参数的电压依赖性向更负的电压偏移，使γ降低0.84倍，并且几乎不改变未被8 nM河豚毒素（TTX）阻断的通道数量No。向细胞外溶液中添加0.1 mM LaCl3会使所有钠门控参数的电压依赖性向更正的电压偏移，使γ降低0.75倍，并且几乎不改变未被8 nM TTX阻断的通道数量No。得出的结论是，由Cl-、NO3-取代引起的外表面电位变化不会改变钠通道外口处的局部Na+浓度，并且几乎不影响TTX与毒素受体的结合。添加LaCl3引起的表面电位变化对TTX结合也没有明显影响。在0.1 mM LaCl3中γ的降低可能是由于La3+与钠通道的直接相互作用。我们的结果表明，在钠通道外口、TTX结合位点和钠通道门附近存在外部固定表面电荷的异质分布。
