Rojas L, Orkand R K
Physiology Department and Center for Molecular and Behavioral Neuroscience, Universidad Central del Caribe, Bayamón, Puerto Rico.
Glia. 1999 Jan 15;25(2):199-203. doi: 10.1002/(sici)1098-1136(19990115)25:2<199::aid-glia10>3.0.co;2-b.
The radial glial cells that span the retina, described by Müller in 1851, have a remarkable distribution of ion channels in adult amphibia that mediate extracellular K+ spatial buffering. 94% of the total membrane conductance of these cells resides in inward rectifier K+ channels in the endfoot processes apposed to the vitreous humour. We now report that this regional specialization is found in Müller cells isolated from adult (>120 day old) bullfrogs but to a far less extent in those from 10-20 day old tadpoles (stages 34-36). Using the cell attached configuration of the patch-clamp technique, we found, in agreement with previous studies in salamanders, that the endfoot of adult cells had 19.2+/-2.4 (mean +/- S.E., n = 81) channels/patch, whereas the soma had 1.81+/-0.28 (n = 21) channels/patch. In the tadpole, the respective values were 4.29+/-0.26 (n = 79) for the endfoot and 2.26+/-0.24 (n = 27) for the soma. The slope conductance of the inward rectifier K+ channel in 115 mM K+, 19.2+/-0.25 pS (n = 205), channel kinetics and the resting membrane potential (-69+/-2.7 mV, n = 224) were similar at both the endfoot and soma of both adults and embryos. We conclude that during development, the K+ conductance of the Müller cell endfoot, but not of the soma, increases due to a selective clustering of inwardly rectifying K+ channels in that specific region of the cell membrane. The properties of the channels change little during the transformation from tadpole to adult bullfrog.
1851年，Müller描述了贯穿视网膜的放射状胶质细胞，在成年两栖动物中，这些细胞具有显著的离子通道分布，可介导细胞外钾离子的空间缓冲。这些细胞总膜电导的94%存在于与玻璃体液相邻的终足突起中的内向整流钾通道中。我们现在报告，这种区域特化在从成年（>120日龄）牛蛙分离的Müller细胞中存在，但在10 - 20日龄蝌蚪（34 - 36阶段）的细胞中程度要低得多。使用膜片钳技术的细胞贴附模式，我们发现，与之前对蝾螈的研究一致，成年细胞的终足每片膜有19.2±2.4（平均值±标准误，n = 81）个通道，而胞体每片膜有1.81±0.28（n = 21）个通道。在蝌蚪中，终足的相应值为4.29±0.26（n = 79），胞体为2.26±0.24（n = 27）。在115 mM钾离子条件下，内向整流钾通道的斜率电导为19.2±0.25 pS（n = 205），通道动力学以及静息膜电位（-69±2.7 mV，n = 224）在成年和胚胎的终足及胞体中均相似。我们得出结论，在发育过程中，Müller细胞终足而非胞体的钾离子电导增加，这是由于内向整流钾通道在细胞膜的特定区域选择性聚集所致。从蝌蚪转变为成年牛蛙的过程中，通道特性变化不大。
