Calcium-Dependent Voltage Transients Evoked by Illumination in the Liverwort Conocephalum conicum

Abstract

The liverwort Conocephalum conicum with anion channels blocked by anthracene-9- carboxylic acid (A-9-C) and potassium channels blocked by tetraethylamm onium (TEA) generates dose-dependent responses to illumination further called voltage transients (VTs). Unlike the action potentials in untreated Conocephalum thalli, VTs do not propagate and cannot be evoked by electrical stimuli. Except A-9-C, two other anion channel inhibitors: ethacrinic and niflumic acids were effective in inducing VTs. These responses were blocked by DCMU, diethylstilbestrol and vanadate, which indicates that the photosynthetic electron transfer chain and the proton pump mediate in their generation. Light-induced VTs were considerably suppressed by calcium channel inhibitors: Mn2+, Gd3+, verapamil and nifedipine, and to a less extent by La 3+ and diltiazem, provided that the incubation lasted more than 2 h. The participation of voltage-indep endent Ca2+-permeable channels in ionic mechanism of VTs is postulated.