Ca²⁺ dependence and La³⁺ interference of ultraviolet radiationinduced K⁺ efflux from rose cells

A low fluence of ultraviolet radiation (UV) causes cultured cells of Rosa damascena Mill cv. Gloire de Guilan to lose intracellular K⁺. This effect required the presence of Ca²⁺ in the medium. A reduction in the concentration of free Ca²⁺ to 10⁻⁵M with ethyleneglycol-bis-(β-aminoethyl-ether)-N.N.N′,N′-tetraacetic acid (EGTA) buffer inhibited the UV-stimulated efflux; this was correlated with a discharge of the membrane potential and a stimulation of the leakage of K⁺ from unirradiated cells. All the same effects were seen with La³⁺ at 0.2 mM. At 0.02 mM La³⁺, the UV-stimulated efflux of K⁺ was blocked without concomitant effects on the membrane potential or K⁺ efflux from control cells. It is suggested that removal of Ca²⁺ blocks or masks the UV-induced leakage of K⁺ by destabilizing the plasma membrane. In addition, La³⁺ may specifically inhibit the UV-stimulated opening of K⁺ or anion channels. (author)