Synchronous intra-Golgi transport induces the release of Ca2+ from the Golgi apparatus

The mechanisms of secretory transport through the Golgi apparatus remain an issue of debate. The precise functional importance of calcium ions (Ca2+) for intra-Golgi transport has also been poorly studied. Here, using different approaches to measure free Ca2+ concentrations in the cell cytosol ([Ca2+]cyt) and inside the lumen of the Golgi apparatus ([Ca2+]GA), we have revealed transient increases in [Ca2+]cyt during the late phase of intra-Golgi transport that are concomitant with a decline in the maximal [Ca2+]GA restoration ability. Thus, this redistribution of Ca2+ from the Golgi apparatus into the cytosol during the movement of cargo through the Golgi apparatus appears to have a role in intra-Golgi transport, and mainly in the late Ca2+-dependent phase of SNARE-regulated fusion of Golgi compartments.