Fluorescence changes of rhodamine 6G associated with chemotactic responses in Tetrahymena pyriformis

Abstract

1. 1. The chemotactic responses in Tetrahymena to various inorganic salts and octanol were examined quantitatively. Tetrahymena exhibited negative chemotaxis to the salts and octanol above respective threshold concentrations. The order of the threshold of salts was NH 4Cl ≅ NaCl > LiCl > KCl > CaCl 2 ≅ MgCl 2 > LaCl 3. 2. 2. Fluorescence intensity of rhodamine 6G added to Tetrahymena suspension increased with increasing concentration of stimuli above respective thresholds. The fluorescence changes were closely correlated with the chemotactic responses for all the chemical stimuli examined. 3. 3. Measurements of the fluorescence intensity of the supernatant of dy- Tetrahymena suspension showed that the dye was taken up by Tetrahymena and the addition of salts led to a release of the dye into an external medium. 4. 4. The adsorption of dye on the liposome also led to the quenching of its fluorescence. Addition of salts to the dye liposome suspension brought about an increase of the fluorescence. The order of the effectiveness was mono-valent < divalent < trivalent. The fluorescence intensity changed linearly with log[K] out in the presence of valinomycin. It was concluded that the changes in fluorescence on rhodamine 6G reflect both changes in the surface potential and those in the intramembrane diffusion potential, which in turn reflect changes in the total membrane potential across the membrane. We suggest that the surface potential as well as the diffusion potential contributes to the changes in the membrane potential in Tetrahymena associated with the chemotactic responses.