Bordey A, Sontheimer H
Department of Neurobiology, University of Alabama at Birmingham, 1719 6th Ave. S., CIRC Rm. 545, Birmingham, AL, USA.
J Membr Biol. 1998 Dec 1;166(3):213-22. doi: 10.1007/s002329900463.
Astrocytes that are recorded in acute tissue slices of rat hippocampus using whole-cell patch-clamp, commonly exhibit voltage-activated Na+ and K+ currents. Some reports have described astrocytes that appear to lack voltage-activated currents and proposed that these cells constitute a subpopulation of electrophysiologically passive astrocytes. We show here that these cells can spontaneously change during a recording unmasking expression of previously suppressed voltage-activated currents, suggesting that such cells do not represent a subpopulation of passive astrocytes. Superfusion of a low Ca2+/EGTA solution was able to reversibly suppress voltage-activated K+ currents in cultured astrocytes. Currents were restored upon addition of normal bath Ca2+. These effects of Ca2+ on both outward and inward K+ currents were dose- and time-dependent, with increasing concentrations of Ca2+ (from 0 to 800 micrometers) leading to a gradual unmasking of voltage-dependent outward and inward K+ currents. The transition from an apparently passive cell to one exhibiting prominent voltage-activated currents was not associated with any changes in membrane capacitance or access resistance. By contrast, in cells in which low access resistance or poor seal accounted for the absence of voltage-activated currents, improvement of cell access was always accompanied by changes in series resistance and membrane capacitance. We propose that spillage of pipette solution containing low Ca2+/EGTA during cell approach in slice recordings and/or poor cell access, lead to a transient masking of voltage-activated currents even in astrocytes that express prominent voltage-activated currents. These cells, however, do not constitute a subpopulation of electrophysiologically passive astrocytes.
使用全细胞膜片钳技术在大鼠海马体急性组织切片中记录的星形胶质细胞，通常表现出电压激活的Na⁺和K⁺电流。一些报告描述了似乎缺乏电压激活电流的星形胶质细胞，并提出这些细胞构成了电生理上被动的星形胶质细胞亚群。我们在此表明，这些细胞在记录过程中可自发变化，使先前被抑制的电压激活电流得以暴露，这表明此类细胞并不代表被动星形胶质细胞亚群。用低Ca²⁺/EGTA溶液灌流能够可逆地抑制培养的星形胶质细胞中的电压激活K⁺电流。加入正常浴液Ca²⁺后电流恢复。Ca²⁺对向外和向内K⁺电流的这些作用呈剂量和时间依赖性，随着Ca²⁺浓度增加（从0到800微摩尔），导致电压依赖性向外和向内K⁺电流逐渐暴露。从明显被动的细胞转变为表现出显著电压激活电流的细胞，与膜电容或输入电阻的任何变化均无关。相比之下，在因低输入电阻或封接不良导致缺乏电压激活电流的细胞中，改善细胞封接总是伴随着串联电阻和膜电容的变化。我们提出，在切片记录中细胞封接过程中含有低Ca²⁺/EGTA的移液管溶液溢出和/或细胞封接不良，即使在表达显著电压激活电流的星形胶质细胞中也会导致电压激活电流的短暂掩盖。然而，这些细胞并不构成电生理上被动的星形胶质细胞亚群。
