Changes in intracellular Ca2+ distribution of rat peritoneal mast cells before and after histamine release

Rat peritoneal mast cells were stained with quin 2, a fluorescent Ca2+ chelator. By means of a fluorescence microscope and real time image processer, it was revealed that the fluorescence derived from the Ca-quin 2 complex was weak in the area occupied by the nucleus and distributed unevenly in the cytoplasm of the resting cells so as to encompass the individual granules. When compound 48/80 or substance P was added in a Ca-free medium, the fluorescence intensity of quin 2 increased markedly all over the cell, suggesting that a large amount of Ca2+ was released from intracellular Ca stores. The increase in the fluorescence intensity produced by compound 48/80 or substance P in a Ca-free medium was inhibited by pretreatment with certain drugs eliciting an increase of c-AMP levels, such as dibutyryl c-AMP and theophylline, or by some anti-allergic drugs providing a membrane stabilizing action.