The regulation and the dynamics of membrane trafficking events have been studied primarily in in vitro models that often do not fully reflect the functional complexity found in a living multicellular organism. Here we used intravital microscopy in the salivary glands of live rodents to investigate regulated exocytosis, a fundamental process in all of the secretory organs. We found that β-adrenergic stimulation elicits exocytosis of large secretory granules, which gradually collapse with the apical plasma membrane without any evidence of compound exocytosis, as was previously described. Furthermore, we show that the driving force required to complete the collapse of the granules is provided by the recruitment of F-actin and nonmuscle myosin II on the granule membranes that is triggered upon fusion with the plasma membrane. Our results provide information on the machinery controlling regulated secretion and show that intravital microscopy provides unique opportunities to address fundamental questions in cell biology under physiological conditions.

Intravital microscopy is an extremely powerful tool that enables imaging several biological processes in live animals. Recently, the ability to image subcellular structures in several organs combin...

Despite the obvious advantages of gold nanoparticles for biomedical applications, controversial and incomplete toxicological data hamper their widespread use. Here, we present the results from an in vivo toxicity study using gold nanoparticles coated with polyethylene glycol (PEG-AuNPs). The pharmacokinetics and biodistribution of PEG-AuNPs were examined in the rat’s liver, lung, spleen, and kidney after a single i.v. injection (0.7 mg/kg) at different time intervals. PEG-AuNPs had a relatively long blood circulation time and accumulated primarily in the liver and spleen, where they remained for up to 28 days after administration. Increased cytoplasmic vacuolation in hepatocytes 24 h and 7 days after PEG-AuNPs exposure and apoptotic-like cells in white splenic pulp 24 h after administration has been detected, however, 28 days post-exposure were no longer observed. In contrast, at this time point, we identified significant changes in lipid metabolism, altered levels of liver injury markers, and elevated monocyte count, but without marked biological relevance. In blood cells, no DNA damage was present in any of the studied time intervals, with the exception of DNA breakage transiently detected in primary kidney cells 4 h post-injection. Our results indicate that the tissue accumulation of PEG-AuNPs might result in late toxic effects.