Monck J R, Oberhauser A F, Alvarez de Toledo G, Fernandez J M
Department of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905.
Biophys J. 1991 Jan;59(1):39-47. doi: 10.1016/S0006-3495(91)82196-8.
The swelling of the secretory granule matrix which follows fusion has been proposed as the driving force for the rapid expansion of the fusion pore necessary for exocytosis. To test this hypothesis, we have combined simultaneous measurements of secretory granule swelling using videomicroscopy with patch clamp measurements of the time course of the exocytotic fusion pore in mast cells from the beige mouse. We show that isotonic acidic histamine solutions are able to inhibit swelling of the secretory granule matrix both in purified secretory granules lysed by electroporation and in intact cells stimulated to exocytose by guanine nucleotides. In contrast to the inhibitory effects on granule swelling, the rate of expansion of the exocytotic fusion pore is unaffected. Therefore, as the rate of granule swelling was more than 20 times slower under these conditions, swelling of the secretory granule matrix due to water entry through the fusion pore cannot be the force responsible for the characteristic rapid expansion of the exocytotic fusion pore. We suggest that tension in the secretory granule membrane, which has recently been demonstrated in fused secretory granules, might be the force that drives the irreversible expansion of the fusion pore.
分泌颗粒融合后基质的肿胀被认为是胞吐作用中融合孔快速扩张的驱动力。为了验证这一假设，我们将利用视频显微镜对分泌颗粒肿胀进行的同步测量与对米色小鼠肥大细胞胞吐融合孔时间进程的膜片钳测量相结合。我们发现，等渗酸性组胺溶液既能抑制经电穿孔裂解的纯化分泌颗粒中的分泌颗粒基质肿胀，也能抑制经鸟嘌呤核苷酸刺激而发生胞吐作用的完整细胞中的分泌颗粒基质肿胀。与对颗粒肿胀的抑制作用相反，胞吐融合孔的扩张速率不受影响。因此，由于在这些条件下颗粒肿胀速率慢了20倍以上，通过融合孔进入的水导致的分泌颗粒基质肿胀不可能是导致胞吐融合孔特征性快速扩张的力量。我们认为，最近在融合的分泌颗粒中得到证实的分泌颗粒膜张力可能是驱动融合孔不可逆扩张的力量。
