Goldman L, Binstock L
J Gen Physiol. 1969 Dec;54(6):741-54. doi: 10.1085/jgp.54.6.741.
The effect of reducing the external sodium concentration, Na, on resting potential, action potential, membrane current, and transient current reversal potential in Myxicola giant axons was studied. Tris chloride was used as a substitute for NaCl. Preliminary experiments were carried out to insure that the effect of Tris substitution could be attributed entirely to the reduction in Na. Both choline and tetramethylammonium chloride were found to have additional effects on the membrane. The transient current is carried largely by Na, while the delayed current seems to be independent of Na. Transient current reversal potential behaves much like a pure Nernst equilibrium potential for sodium. Small deviations from this behavior are consistent with the possibility of some small nonsodium component in the transient current. An exact P(Na)/P(K) for the transient current channels could not be computed from these data, but is certainly well greater than unity and possibly quite large. The peak of the action potential varied with Na as expected for a sodium action potential with some substantial potassium permeability at the time of peak. Resting membrane potential is independent of Na. This finding is inconsistent with the view that the resting membrane potential is determined only by the distribution of K and Na, and P(Na)/P(K). It is suggested that P(Na)/P(K)'s obtained from resting membrane potential-potassium concentration data do not always have the physical meaning generally attributed to them.
研究了降低外部钠浓度Na对黏液虫巨轴突静息电位、动作电位、膜电流和瞬态电流反转电位的影响。用三氯化物替代氯化钠。进行了初步实验以确保三氯化物替代的影响完全归因于Na的降低。发现胆碱和四甲基氯化铵对膜有额外影响。瞬态电流主要由钠携带，而延迟电流似乎与Na无关。瞬态电流反转电位的行为很像钠的纯能斯特平衡电位。与这种行为的小偏差与瞬态电流中一些小的非钠成分的可能性一致。无法从这些数据计算出瞬态电流通道的确切P(Na)/P(K)，但肯定远大于1，可能相当大。动作电位的峰值随Na变化，正如在峰值时有一定钾通透性的钠动作电位所预期的那样。静息膜电位与Na无关。这一发现与静息膜电位仅由K和Na的分布以及P(Na)/P(K)决定的观点不一致。有人认为，从静息膜电位-钾浓度数据获得的P(Na)/P(K)并不总是具有通常赋予它们的物理意义。
