Role of Microtubules on Ca2+ Release from the Endoplasmic Reticulum and Associated Histamine Release from Rat Peritoneal Mast Cells

In order to study the role of cytoskeletons on histamine release from mast cells, the effects of cytoskeleton-inhibiting agents were investigated. Since neither colchicine, vinblastine nor cytochalasin D was effective in inhibiting the IP3 formation, it is possible that neither microtubules nor microfilaments of rat peritoneal mast cells participate in the initial membrane events of the histamine release. However, both colchicine and vinblastine, but not cytochalasin D, were effective in inhibiting Ca2+ release from the intracellular Ca store. It was accordingly suggested that the microtubules, rather than microfilaments, are intimately related to the Ca2+ releasing process from the endoplasmic reticulum. The fluorescence intensity of the mast cells stained with FITC-labeled anti-tubulin antibody reflects the amount of tubulin polymers inside the cell, and colchicine treatment decreased the fluorescence intensity, indicating that colchicine is effective in depolymerizing the microtubules of rat mast cells. By contrast, the amount of tubulin polymer in the mast cells increased by compound 48/80, indicating that the rearrangement of microtubules took place in the mast cells, leading to histamine release. When permeabilized mast cells were exposed to potassium antimonate solution, microtubules attached themselves to the endoplasmic reticulum and many Ca antimonate dots were observed. From the present results, it was concluded that microtubules play an important role in the processes leading to Ca2+ release from the intracellular Ca store and subsequent histamine release.