Carrasquer G, Wu X Y, Kissel D, Rehm W S, Schwartz M, Dinno M A
Department of Medicine (Nephrology), University of Louisville, Louisville, KY 40292.
Biochim Biophys Acta. 1989 Jun 26;982(1):73-8. doi: 10.1016/0005-2736(89)90175-2.
Addition of 10(-5) M amphotericin B to the tear solution of an in vitro preparation of the frog cornea increased the transepithelial conductance, gt, and decreased the apical membrane fractional resistance, f(R0), in the presence or absence of tear Na+ and Cl-. In the presence of tear Na+ and Cl-, amphotericin B increased the short-circuit current, Isc, from 3.9 to 8.8 microA.cm-2 and changed the intracellular potential, V0, from -48.5 to -17.9 mV probably due to a higher increase in the Na+ than in the K+ conductance. In the absence of tear Na+ and Cl-, amphotericin B decreased Isc from 5.5 to about 0 microA.cm-2 due to K+ (and possibly Na+) flux from cell to tear and changed V0 from -35.4 to -63.6 mV due to the increase in conductance of both ions. Increase in the tear K+ from 4 to 79 mM (in exchange for choline), in the presence of amphotericin B and absence of tear Na+ and Cl-, decreased f(R0) from 0.09 to 0.06, increased gt from 0.23 to 0.31 mS, increased Isc from 0.63 to 7.3 microA.cm-2, and changed V0 from -65.5 to -17.3 mV due to the change in EK in the presence of a high conductance in the tear membrane. Similar effects were observed with an increase of tear Na+. Results support the concept that the Na+ conductance opened by amphotericin B in the apical membrane is greater than the K+ conductance. Previously observed transepithelial effects of the ionophore may be explained mostly on the basis of its effect on the apical membrane.
在青蛙角膜体外制备物的泪液中添加10⁻⁵ M两性霉素B，无论泪液中是否存在Na⁺和Cl⁻，均可增加跨上皮电导（gt）并降低顶端膜分数电阻（f(R0)）。在泪液存在Na⁺和Cl⁻的情况下，两性霉素B使短路电流（Isc）从3.9增加到8.8 μA·cm⁻²，并使细胞内电位（V0）从 -48.5 mV变为 -17.9 mV，这可能是由于Na⁺电导的增加高于K⁺电导。在泪液中不存在Na⁺和Cl⁻的情况下，两性霉素B使Isc从5.5降低到约0 μA·cm⁻²，这是由于K⁺（可能还有Na⁺）从细胞流向泪液，并且由于两种离子电导的增加，V0从 -35.4 mV变为 -63.6 mV。在两性霉素B存在且泪液中不存在Na⁺和Cl⁻的情况下，将泪液中的K⁺从4 mM增加到79 mM（用胆碱替代），f(R0)从0.09降低到0.06，gt从0.23增加到0.31 mS，Isc从0.63增加到7.3 μA·cm⁻²，并且由于泪液膜中高电导存在时EK的变化，V0从 -65.5 mV变为 -17.3 mV。泪液中Na⁺增加时也观察到类似的效果。结果支持这样的概念，即两性霉素B在顶端膜中打开的Na⁺电导大于K⁺电导。先前观察到的离子载体的跨上皮效应大多可以基于其对顶端膜的作用来解释。
