Effects of NaF on the calcium ion concentration in isolated midgut cells of Bombyx mori

The free Ca²⁺ concentration in midgut cells isolated from fifth instar larvae of Bombyx mori was found to be 592 nM as measured by addition of fura-2/AM to the culture medium. When the cultured cells were loaded with NaF during the measurement, the Ca²⁺ concentration decreased to half the original value in 90 sec. This effect of NaF was completely blocked when verapamil, a competitor for the membrane transport system, was added, indicating that free Ca²⁺ was transported out of the cells after the addition of NaF. This finding may be of importance from the viewpoint of the protection of sericulture from polluted air containing fluoride compounds.