Mills L R, Morris C E
Playfair Neuroscience Unit, The Toronto Hospital Research Institute and Department of Physiology, University of Toronto, 11-430 TWH 399 Bathurst St, Toronto, Ontario, Canada M5T 2S8.
J Membr Biol. 1998 Dec 1;166(3):223-35. doi: 10.1007/s002329900464.
When neurons swell and shrink they extensively reorganize their plasma membrane. A striking aspect of these membrane dynamics is the transient appearance of vacuole-like dilations (VLDs) which, counterintuitively, expand as the neurons shrink. Here, confocal microscopy of cultured molluscan (Lymnaea) neurons was used in conjunction with aqueous phase and membrane dyes to examine changing VLD membrane topology as VLDs form, reverse or recover. We show that VLDs start as discrete invaginations at the adherent surface, so VLD and plasma membranes are initially contiguous. Over the next few minutes VLDs expand and penetrate the cytoplasm. At the substratum, the mouths of VLDs develop into irregular annuli of motile adherent processes whereas deeper in the cytoplasm, VLD membrane profiles are smooth. Subsequently VLDs spontaneously shrink; as this recovery proceeds, constriction of the motile VLD mouth leads to the internalization of plasma membrane. Washout experiments with aqueous phase dyes demonstrated that VLD constriction yields bona fide vacuoles, i.e., membrane-bound compartments isolated from the external medium. VLDs can also be experimentally eliminated by returning cells to swelling conditions; this reversal process drives membrane back to the surface. VLD formation and reinternalization of VLD membrane can be seen as aspects of plasma membrane surface area regulation. We postulate that area adjustments, driven by regional membrane tension differences, become noticeable when excessive perturbations overload normal membrane reprocessing steps. Both the changes in VLD membrane topology, and previously established capacitance changes accompanying cell shrinking and swelling, argue that osmomechanically perturbed neurons regulate their surface area as their volume changes.
当神经元肿胀和收缩时，它们会广泛地重新组织其质膜。这些膜动力学的一个显著方面是液泡样扩张（VLDs）的短暂出现，与直觉相反的是，当神经元收缩时VLDs会扩张。在这里，结合水相和膜染料，对培养的软体动物（椎实螺）神经元进行共聚焦显微镜检查，以观察VLDs形成、逆转或恢复时其膜拓扑结构的变化。我们发现，VLDs起始于附着表面的离散内陷，因此VLDs和质膜最初是连续的。在接下来的几分钟内，VLDs扩张并穿透细胞质。在基质处，VLDs的开口发展为可移动附着突起的不规则环，而在细胞质较深处，VLD膜轮廓是光滑的。随后VLDs自发收缩；随着恢复过程的进行，可移动的VLD开口的收缩导致质膜内化。用水相染料进行的洗脱实验表明，VLD收缩产生真正的液泡，即与外部介质隔离的膜结合区室。通过将细胞恢复到肿胀状态，也可以通过实验消除VLDs；这个逆转过程将膜带回表面。VLD的形成和VLD膜的再内化可被视为质膜表面积调节的方面。我们推测，当过度扰动使正常的膜再加工步骤不堪重负时，由区域膜张力差异驱动的面积调整就会变得明显。VLD膜拓扑结构的变化，以及先前确定的伴随细胞收缩和肿胀的电容变化，都表明渗透机械扰动的神经元会随着其体积的变化调节其表面积。
