Analysis of the late steps of exocytosis: biochemical and total internal reflection fluorescence microscopy (TIRFM)...

1. Time with Julie in his laboratory at the NIH in the early 1970s is remembered. The experience led to a life-long interest in the regulation of catecholamine secretion. Here are summarized aspects of this work. 2. The relationship between ATP-dependent priming of exocytosis and the polyphosphoinositides is reviewed. In addition, studies are summarized in which total internal reflection fluorescent microscopy (TIRFM) was used to visualize secretory granule behavior before exocytosis and individual exocytotic events. 3. Quantitative optical analysis indicates that chromaffin granule motion is highly restricted but regulated. Granules can undergo significant motion in the 100 ms prior to fusion and interactions with the plasma membrane leading to fusion can occur within this time. The small motions may permit granules adjacent to the plasma membrane to repetitively sample microdomains of the plasma membrane, thereby increasing the probability of fruitful interactions that lead to fusion.