We are continuing to study the mast cell of the beige mouse, an animal model for the Chediak-Higashi syndrome in man. We study this cell because of its very large secretory granules, like the large granules of the neutrophils in the diseased state. One defect in that immuno-suppressed syndrome is failure in secretion. The large size of the beige mouse mast cell make possible detailed analysis of their exocytosis to the plasma membrane. Last year, we developed an instrumental array capable of simultaneous physiologic and anatomic real-time measurements of living cells with control of the internal millieu, using it to measure the capacitance of secretory and phagocytic peritoneal cells from the internally perfused mast cell from the beige mouse. Thus, we can combine biochemistry, anatomy, and physiology by performing perfusion studies on single active cells while recording both optical information (image, exocytosis, endocytosis, contraction), and electrical information (ionic currents, voltage clamp, capacitance) with 17 msec resoultion. Preliminary studies reveal that the fusion of the secretory granule preceeds the swelling of that vesicle by 17-150 milliseconds. Granules which have been shrunken by hyperosmotic solutions also fuse to the cell membrane well before detectable swelling. Apparently in this system vesicle swelling is not needed for membrane fusion but may be required for the release of secretory products.
