Methods
the laser-trap forcemetry and the evanescent-wave fluorescence microscopy. With a laser beam, we trapped a micro bead in the vicinity of a cell (with 1 microm of separation) and observed movements of the bead optically. Electrical stimulation of the cell induced many of rapid and transient movements of the bead in a direction away from the cell surface. Upon the same stimulation, secretory vesicles stained with a fluorescent probe, acridine orange, and excited under the evanescent field illumination, showed a flash-like response: a transient increase in fluorescence intensity associated with a diffuse cloud of brightness, followed by a complete disappearance. These mechanical and fluorescence transients indicate a directional flow of substances. Blockers of the Cl(-) channel suppressed the rates of both responses in a characteristic way but not exocytotic fusion itself. Immunocytochemical studies revealed the presence of Cl(-) and K(+) channels on the vesicle membranes. These