Bader C R, Bertrand D
J Physiol. 1984 Feb;347:611-31. doi: 10.1113/jphysiol.1984.sp015086.
Solitary rod inner segments were obtained by enzymic dissociation of the tiger salamander retina. Ih, an inward current activated by membrane hyperpolarization, was studied using the single-pipette voltage-clamp technique with patch pipettes. In order to investigate Ih in isolation from voltage-dependent potassium and calcium currents, it was necessary to superfuse with a solution containing TEA and cobalt. When the solution in the patch pipette contained 45 mM-KCl and 50 mM-NaCl, the characteristics of Ih were indistinguishable from those previously described with fine-tip micro-electrodes: the reversal potential was near-30 mV and Ih was blocked by extracellular caesium and enhanced by an increase in the extracellular potassium concentration. The increase in Ih observed when the extracellular potassium concentration is raised is due to an increase in conductance and in driving force. Replacement of sodium in the patch pipette with choline caused a 15 mV displacement of the reversal potential for Ih in the depolarized direction. When using sodium-free patch pipettes, replacement of extracellular sodium displaced the reversal potential for Ih to -74 mV, a value in the range of the potassium equilibrium potential in solitary inner segments. Intracellular or intra- and extracellular sodium substitution affected neither the activation range of Ih nor the maximum conductance. From points 3-6 it can be concluded that Ih is carried mainly, if not exclusively, by sodium and potassium and that the channel responsible for Ih is insensitive to modifications of the intra- or extracellular sodium concentration. The results of long-term hyperpolarization, of partial block with caesium and of total sodium substitution are consistent with sodium and potassium permeating the same type of channel.
通过对虎螈视网膜进行酶解获得单个杆状内节。使用膜片吸管的单吸管电压钳技术研究了由膜超极化激活的内向电流Ih。为了在与电压依赖性钾电流和钙电流分离的情况下研究Ih，有必要用含有四乙铵（TEA）和钴的溶液进行灌流。当膜片吸管中的溶液含有45 mM - KCl和50 mM - NaCl时，Ih的特性与先前用尖细微电极描述的特性没有区别：反转电位接近 - 30 mV，Ih被细胞外铯阻断，并随着细胞外钾浓度的增加而增强。当细胞外钾浓度升高时观察到的Ih增加是由于电导和驱动力的增加。用胆碱替代膜片吸管中的钠会使Ih的反转电位在去极化方向上偏移15 mV。当使用无钠膜片吸管时，细胞外钠的替代将Ih的反转电位偏移到 - 74 mV，这是单个内节中钾平衡电位范围内的值。细胞内或细胞内和细胞外钠替代既不影响Ih的激活范围也不影响最大电导。从第3 - 6点可以得出结论，Ih主要（如果不是唯一）由钠和钾携带，并且负责Ih的通道对细胞内或细胞外钠浓度的改变不敏感。长期超极化、铯部分阻断和全钠替代的结果与钠和钾通过同一种通道渗透一致。
