In this paper they investigate I) the distribution of mitochondria and the ER in chromaffin cells, and ii) how this distribution plays a role in exocytosis.
Exocytosis occurs in response to elevations of cytoplasmic calcium levels and requires energy. Mitochondria-ER interactions are important in shaping cellular calcium signals and therefore the distribution of these two organelles in the cell may well influence exocytotic events.
Mitochondria in chromaffin cells exist in two main populations, one of higher density in the cortical region and another one in the perinuclear region. Mitochondria were noticably smaller in size in the cortical region. The two populations showed different mobilities, mitochondria in the perinuclear area were faster and moved through F-actin and microtubular structures.
Distribution of the ER is more uniform (though the density increases gradually from the cortical zone to regions close to the nucleus) and ER elements were also smaller in cortical regions.
They find that the cortical populations of mitochondria and ER themselves consists of two subpopulations, one close to exocytotic sites and one further away. The local cortical subpopulations could be directly involved in the regulation of calcium signals and ATP supply in the immediate vicinity of exocytotic sites.