Kinetics of efflux of K⁺ from cultured rose cells treated with ultraviolet light

Abstract

Irradiation of cultured rose (Rosa damascena Mill. cv. Gloire de Guilan) cells with ultraviolet light caused of loss of K+, which occurred with sigmoid kinetics. The kinetics of loss of K+ were not changed when the extracellular concentration of K+ was held constant during the period of efflux. Furthermore, the rate of loss of K+ was approximately the same even though the K+ concentration in the medium was increased from 0.1 to 10 mM. The kinetics of uptake of the lipophilic methyltriphenylphosphonium cation, an indicator of the plasma membrane potential, were linear throughout the period of K+ efflux, suggesting that the starting and stopping of K+ efflux do not reflect a passive response to changes in the membrane potential of the cells. The results are interpreted in terms of activation and inactivation of an efflux channel or pump for K+.

Effect of washing on the plasma membrane and on stress reactions of cultured rose cells

“…In these studies, the cells have generally been washed three times with a solution of lmM CaCI 2 plus 0.1mM KC1, with incubations of at least 30 min between washings and a final incubation of 2 h. The original reason for the washings was to reduce the background level of K + in order to allow more sensitive measurements of K + efflux from the cells after UV irradiation. A later study demonstrated that the UV-stimulated efflux of K + was as great at 10mM external K + as it was at 0.1mM K ÷ (Huerta & Murphy 1989). On the other hand, preliminary studies suggested that the specific activity of plasma membrane ATPase isolated from washed cells differed from that isolated from unwashed cells.…”