Miyamoto S, Fujime S
Mitsubishi Kasei Institute of Life Sciences, Tokyo, Japan.
Biophys J. 1990 Mar;57(3):615-9. doi: 10.1016/S0006-3495(90)82577-7.
In the process of secretion, the membrane of secretory granules is expected to change its elastic behavior. Elastic modulus of the membrane of zymogen granules, prepared from the rat pancreas acinar cell, was measured by an osmotic swelling method. The elastic modulus of the granule membrane at pCa 8 reduced from the maximal value of 230 dyn/cm at pH 6.0 to almost zero at pH 7.5. In a cytosol of an acinar cell, calcium ions play an important role as a second messenger in secretion. The elastic modulus of the granule membrane reduced in a sigmoidal fashion at pCa between 7.0 and 6.0. This range of pCa corresponds to a physiological rise of free Ca2+ concentrations in the cell cytosol when stimulated by external secretagogues. Reduction of the elastic modulus indicates that the state of the granule membrane switches to a more flexible one in which the granule is easy to appose to the cell plasma membrane and then swell as a final step of exocytosis.
在分泌过程中，分泌颗粒的膜预期会改变其弹性行为。通过渗透肿胀法测量了从大鼠胰腺腺泡细胞制备的zymogen颗粒膜的弹性模量。在pCa 8时颗粒膜的弹性模量从pH 6.0时的最大值230 dyn/cm降低到pH 7.5时几乎为零。在腺泡细胞的胞质溶胶中，钙离子作为分泌中的第二信使发挥重要作用。在pCa为7.0至6.0之间时，颗粒膜的弹性模量呈S形降低。这个pCa范围对应于细胞胞质溶胶在受到外部促分泌剂刺激时游离Ca2+浓度的生理性升高。弹性模量的降低表明颗粒膜的状态转变为更具柔韧性的状态，在这种状态下颗粒易于与细胞质膜贴合，然后肿胀，作为胞吐作用的最后一步。
