Weber A, Siemen D
Physiologisches Institut, Justus-Liebig-Universität, Giessen, Federal Republic of Germany.
Pflugers Arch. 1989 Sep;414(5):564-70. doi: 10.1007/BF00580992.
The non-selective channel for monovalent cations of cultured brown adipocytes was studied concerning its permeability to alkali metal ions, NH4+, Tris+, Ca2+, and Ba2+. Experiments were done by means of the patch clamp technique using inside-out patches. With symmetrically increasing sodium concentrations the ion fluxes saturated. They are described by a dissociation constant (KNa) of 155 mmol/l and a maximum single channel conductance of 50 pS. Permeabilities were determined in relation to those for sodium yielding values of 0.80 for potassium and 1.55 for ammonium. The complete permeability sequence for ammonium and the alkali metals is: NH4+ greater than Na+ greater than Li+ greater than K+ greater than or equal to Rb+ congruent to Cs+ . Ca2+ and Ba2+ as well as the buffer ion Tris+ are not able to pass the channel measurably. It is shown that the conductance behaviour of the non-selective channel is not sufficiently described by the Goldman-Hodgkin-Katz theory. Deviations from independence are saturation with increased activity of the permeant ion and non-linear current voltage relations in symmetrical solutions. A simple two barrier model with one binding site in the center of the electric field is shown to be more appropriate.
对培养的棕色脂肪细胞单价阳离子非选择性通道的碱金属离子、NH4+、Tris+、Ca2+和Ba2+通透性进行了研究。实验采用膜片钳技术的内面向外膜片进行。随着钠离子浓度对称增加，离子通量饱和。其解离常数（KNa）为155 mmol/l，单通道最大电导为50 pS。测定了相对于钠离子的通透性，钾离子的通透性值为0.80，铵离子为1.55。铵离子和碱金属的完整通透性顺序为：NH4+＞Na+＞Li+＞K+≥Rb+≅Cs+。Ca2+、Ba2+以及缓冲离子Tris+不能通过该通道被检测到。结果表明，戈德曼-霍奇金- Katz理论不能充分描述非选择性通道的电导行为。与独立性的偏差表现为通透离子活性增加时的饱和以及对称溶液中的非线性电流电压关系。结果表明，一个在电场中心有一个结合位点的简单双屏障模型更合适。
