Strontium ions as a probe for the role of alkaline-earth metal ions in histamine secretion [proceedings].

granule-membrane surface as it undergoes exocytosis is dramatically decreased (Howell & Tyhurst, 1977). Incubation of isolated granules with 1-2m~-CaCI, did not produce a visible decrease in the number of anionic sites, although as shown by Dean (1974), even the small decrease in charge which could be expected after addition of 1 mM-CaZ+ would be sufficient to produce a 50-fold increase in the number of fusions of granule and plasma membranes. It is certainly attractive to speculate that once a granule has been transported to a position very close to the plasma membrane by the action of microtubules, possibly also involving calcium, it will be maintained at a point close to the membrane by the equilibrium between van der Waals forces of attraction and electrostatic repulsion (Dean, 1975). The rise in cytosolic CaZ+ concentrations, which results from stimulation of secretion, will then decrease the surface charge and electrostatic repulsion, and allow fusion of granule and plasma membrane to occur.