CONTROL OF EXOCYTOSIS IN SEA URCHIN EGGS BY OSMOTIC STRESS

我们已经验证了膜下颗粒融合到细胞中的假说， 膜是由颗粒渗透压，泡状肿胀， 在颗粒囊泡和膜之间的接触点处的膜穿孔 细胞膜 我们研究海胆卵皮质颗粒胞吐作用， 微分干涉显微镜，相位差 旋转阴影快速冷冻电镜 冷冻断裂复制品和细胞内记录来测量细胞 电容和电位。 我们发现，胞吐作用被阻止时， 将卵周围培养基的渗透压从1 μ l提高到2 μ l kg-1. 高渗透压还可阻止细胞内钙依赖性胞吐作用， 体外 既往高渗透压钙治疗触发融合 当恢复正常的渗透压时，即使在 稀释 钙的加入导致皮质颗粒膨胀， 通过计算机图像分析显示。 膜的大量增加 通常伴随融合的电容在激活的卵中不存在 在高渗透压溶液中。 我们的数据与这个想法一致 分泌颗粒必须膨胀以与质膜融合， 支持一个假设的驱动聚变步骤， 胞吐作用

We have examined the hypothesis that submembrane granular fusion to cell membranes is driven by granular osmotic pressure, vesicular swelling, and membrane performation at the point of contact between granular vesicle and cell membrane. WE examine sea urchine egg cortical granule exocytosis with differential interference contrast light microscopy, phase contrast microscopy, electron microscopy of rotary-shadowed rapidly-frozen freeze-fracture replicas, and intracellular recording to measure cell capacitance and potential. We find that exocytosis is prevented when the osmolality of the medium surrounding the eggs is raised from 1 to 2 osmol kg-1. High osmolality also prevents calcium-dependent exocytosis in vitro. Prior treatment with calcium at high osmolality triggers fusion when normal osmolality is restored, even if calcium is removed before dilution. Addition of calcium causes the cortical granules to swell, as revealed by computer image analysis. The large increase in membrane capacitance which normally accompanies fusion is absent in eggs activated in solutions of high osmolality. Our data are consistent with the idea that a secretory granule must swell to fuse with the plasma membrane and support the hypothesis of an osmotically driven fusion step during exocytosis.