Development of Evanescence Microscope and Test of the Quantal Hypothesis for Exocytosis

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Aiming at development of a user-friendly high-performance evanescence microscope based on an ultra-high NA lens, we compared three methods of introducing the illumination light to the microscope. A fiber-illumination method was advantageous in safety, field size, and easy handling, over a direct-illumination method, but was costly and slightly unstable. Using an evanescence microscope, we examined the exocytosis in chromaffin cells and beta cells. In both types of the cell, a fluorescent probe was released from vesicles with a flash response. The flash response was variable in amplitude depending on vesicles. It reflected water secretion from the vesicles. By laser-trap forcemetry, we demonstrated a small force exerted on water by the cell upon stimulation. The contents of vesicles are released not by a simply diffusion but by a water ejection from the vesicles. The strength of the ejecting force varied with vesicles as the density of Cl channels on the vesicle membrane examined by an immuno-staining technique varied. Cl channel blockers suppressed the flash response without suppressing the exocytosis. In beta cells, vesicle moved along the membrane immediately after its exocytotic response, suggesting a continuous release of vesicle contents. These findings are incompatible with the so-called quantal hypothesis. In endocrine cells, modulation for the secretory function is evolved in a highly complex manner so that fine adaptations to inner and outer environments are made possible.