Pérez-Cornejo P, Begenisich T
University of Rochester Medical School, Department of Physiology, New York 14642.
Biophys J. 1994 Jun;66(6):1929-38. doi: 10.1016/S0006-3495(94)80986-5.
We have investigated some of the permeation properties of the pore in Shaker K channels. We determined the apparent permeability ratio of K+, Rb+, and NH4+ ions and block of the pore by external Cs+ ions. Shaker channels were expressed with the baculovirus/Sf9 expression system and the channel currents measured with the whole-cell variant of the patch clamp technique. The apparent permeability ratio, PRb/PK, determined in biionic conditions with internal K+, was a function of external Rb+ concentration. A large change in PRb/PK occurred with reversed ionic conditions (internal Rb+ and external K+). These changes in apparent permeability were not due to differences in membrane potential. With internal K+, PNH4/PK was not a function of external NH4+ concentration (at least over the range 50-120 mM). We also investigated block of the pore by external Cs+ ions. At a concentration of 20 mM, Cs+ block had a voltage dependence equivalent to that of an ion with a valence of 0.91; this increased to 1.3 at 40 mM Cs+. We show that a 4-barrier, 3-site permeation model can simulate these and many of the other known properties of ion permeation in Shaker channels.
我们研究了摇椅型钾通道中孔的一些渗透特性。我们测定了钾离子、铷离子和铵离子的表观渗透率比值以及外部铯离子对孔的阻断作用。摇椅型通道通过杆状病毒/Sf9表达系统进行表达，并使用膜片钳技术的全细胞变体测量通道电流。在内部为钾离子的双离子条件下测定的表观渗透率比值PRb/PK是外部铷离子浓度的函数。在离子条件反转（内部为铷离子，外部为钾离子）时，PRb/PK发生了很大变化。这些表观渗透率的变化并非由于膜电位的差异。当内部为钾离子时，PNH4/PK不是外部铵离子浓度的函数（至少在50 - 120 mM范围内）。我们还研究了外部铯离子对孔的阻断作用。在浓度为20 mM时，铯离子阻断具有相当于价态为0.91的离子的电压依赖性；在40 mM铯离子时，该值增加到1.3。我们表明，一个四屏障、三位点的渗透模型可以模拟摇椅型通道中离子渗透的这些以及许多其他已知特性。
