Fox J A, Pfeffer B A, Fain G L
Jules Stein Eye Institute, University of California, Los Angeles School of Medicine 90024.
J Gen Physiol. 1988 Feb;91(2):193-222. doi: 10.1085/jgp.91.2.193.
We have applied patch-clamp techniques to on-cell and excised-membrane patches from human retinal pigment epithelial cells in tissue culture. Single-channel currents from at least four ion channel types were observed: three or more potassium-selective channels with single-channel slope conductances near 100, 45, and 25 pS as measured in on-cell patches with physiological saline in the pipette, and a relatively nonselective channel with subconductance states, which has a main-state conductance of approximately 300 pS at physiological ion concentrations. The permeability ratios, PK/PNa, measured in excised patches were 21 for the 100-pS channels, 3 for the 25-pS channels, and 0.8 for the 300-pS nonselective channel. The 45-pS channels appeared to be of at least two types, with PK/PNa's of approximately 41 for one type and 3 for the other. The potassium-selective channels were spontaneously active at all potentials examined. The average open time for these channels ranged from a few milliseconds to many tens of milliseconds. No consistent trend relating potassium-selective channel kinetics to membrane potential was apparent, which suggests that channel activity was not regulated by the membrane potential. In contrast to the potassium-selective channels, the activity of the nonselective channel was voltage dependent: the open probability of this channel declined to low values at large positive or negative membrane potentials and was maximal near zero. Single-channel conductances observed at several symmetrical KCl concentrations have been fitted with Michaelis-Menten curves in order to estimate maximum channel conductances and ion-binding constants for the different channel types. The channels we have recorded are probably responsible for the previously observed potassium permeability of the retinal pigment epithelium apical membrane.
我们已将膜片钳技术应用于组织培养的人视网膜色素上皮细胞的全细胞和膜片标本。观察到至少四种离子通道类型的单通道电流：在移液管中加入生理盐水的全细胞标本中测量，有三种或更多种钾选择性通道，其单通道斜率电导分别接近100、45和25 pS，还有一种具有亚电导状态的相对非选择性通道，在生理离子浓度下其主态电导约为300 pS。在膜片标本中测得的通透率PK/PNa，100-pS通道为21，25-pS通道为3，300-pS非选择性通道为0.8。45-pS通道似乎至少有两种类型，一种类型的PK/PNa约为41，另一种为3。钾选择性通道在所有检测电位下均自发激活。这些通道的平均开放时间从几毫秒到几十毫秒不等。未观察到钾选择性通道动力学与膜电位之间的一致趋势，这表明通道活性不受膜电位调节。与钾选择性通道相反，非选择性通道的活性是电压依赖性的：该通道的开放概率在大的正膜电位或负膜电位时降至低值，在接近零电位时最大。在几种对称KCl浓度下观察到的单通道电导已用米氏曲线拟合，以估计不同通道类型的最大通道电导和离子结合常数。我们记录的这些通道可能是先前观察到的视网膜色素上皮顶端膜钾通透性的原因。
