CONTROL OF EXOCYTOSIS IN SEA URCHIN EGGS BY OSMOTIC STRESS

我们检验了亚膜下颗粒融合到细胞的假说 膜是由颗粒渗透压、囊泡膨胀和 颗粒囊泡与膜接触点的膜性能 细胞膜。我们检查海胆卵皮质颗粒胞吐。 差分干涉对比光学显微镜，相位对比 旋转阴影快速冷冻的显微镜、电子显微镜 冷冻断裂复制品和细胞内记录以测量细胞 电容和电势。我们发现胞吐作用在以下情况下被预防 卵子周围培养液的渗透压从1提高到2 Kg-1。高渗透压也可防止钙依赖性胞吐。 体外培养。在高渗透压下预先用钙治疗会触发融合 当正常渗透压恢复时，即使之前去除了钙 稀释。添加钙会导致皮质颗粒肿胀，AS 通过计算机图像分析揭示。膜的大幅增加 在激活的鸡蛋中，通常伴随融合的电容是缺失的 在高渗透压的溶液中。我们的数据与我们的想法一致 分泌颗粒必须膨胀才能与质膜融合， 支持渗透驱动融合步骤的假说 胞吐。

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.