Kreisman N R, Olson J E
Department of Physiology and Neuroscience Program SL-39, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112, USA.
Neuroscience. 2003;120(3):635-42. doi: 10.1016/s0306-4522(03)00359-2.
Cell volume regulation has been studied in neuronal and glial cultures but little is known about volume regulation in brain tissue with an intact extracellular space. We investigated volume regulation in hippocampal slices maintained in an interface chamber and exposed to hypo-osmotic medium. Relative changes in intracellular and extracellular volume were measured respectively as changes in light transmittance and extracellular resistance. Slices exposed to hypo-osmotic medium (200-240 mOsm/L) showed a decrease in light transmittance, which occasionally was preceded by a brief transient increase. However, hypo-osmotic exposure was always accompanied by a monotonic increase in extracellular resistance. Peak changes in light transmittance and extracellular resistance occurred at 15-20 min following exposure to hypo-osmotic medium. Optical evidence of volume regulation (RVD) was observed in six of 12 slices and occurred over the next 60-90 min. We hypothesized that the relatively low incidence of RVD was related to depletion of taurine, an osmolyte known to play an important role in volume regulation, during preparation of the slices. Indeed, taurine levels in freshly prepared slices were <50% of those reported in intact hippocampus. Incubation of slices in 1 mM taurine restored taurine to levels observed in situ and increased both the likelihood and magnitude of RVD in hypo-osmotic medium. Inhibition of taurine flux with 100 microM 5-nitro-2-(3 phenylpropylamino) benzoic acid blocked both RVD and the transient undershoot of volume commonly associated with return of swollen slices to iso-osmotic medium. Taurine treatment had no effect on levels of several other amino acids but preserved slice potassium content. The results indicate a critical role for cellular taurine during hypo-osmotic volume regulation in hippocampal slices. Inconsistencies between optical measurements of cellular volume changes and electrical measurements of extracellular space are likely to result from the complex nature of light transmittance in the interface slice preparation.
细胞体积调节已在神经元和神经胶质细胞培养物中进行了研究，但对于具有完整细胞外空间的脑组织中的体积调节知之甚少。我们研究了置于界面室并暴露于低渗培养基中的海马切片的体积调节。细胞内和细胞外体积的相对变化分别作为透光率和细胞外电阻的变化来测量。暴露于低渗培养基（200 - 240 mOsm/L）的切片显示透光率降低，偶尔在此之前会有短暂的短暂增加。然而，低渗暴露总是伴随着细胞外电阻的单调增加。暴露于低渗培养基后15 - 20分钟出现透光率和细胞外电阻的峰值变化。在12个切片中的6个中观察到了体积调节（RVD）的光学证据，并且在接下来的60 - 90分钟内发生。我们推测RVD发生率相对较低与切片制备过程中牛磺酸的消耗有关，牛磺酸是一种已知在体积调节中起重要作用的渗透剂。事实上，新鲜制备的切片中的牛磺酸水平低于完整海马体中报道水平的50%。将切片在1 mM牛磺酸中孵育可使牛磺酸恢复到原位观察到的水平，并增加了在低渗培养基中RVD的可能性和幅度。用100 microM 5 - 硝基 - 2 -（3 - 苯丙基氨基）苯甲酸抑制牛磺酸通量可阻断RVD以及通常与肿胀切片恢复到等渗培养基相关的体积短暂下冲。牛磺酸处理对其他几种氨基酸的水平没有影响，但保留了切片中的钾含量。结果表明细胞牛磺酸在海马切片低渗体积调节过程中起关键作用。细胞体积变化的光学测量与细胞外空间的电学测量之间的不一致可能是由于界面切片制备中透光率的复杂性质所致。
