Excitation-induced dynamics of external pH pattern in Chara corallina cells and its dependence on external calcium concentration

Abstract

The influence of cell excitation and external calcium level on the dynamics of light-induced pH bands along the length of Chara corallina cells is studied in the present paper. Generation of an action potential (AP) transiently quenched these pH patterns, which was more pronounced at 0.05–0.1 mM Ca²⁺ than at higher concentrations of Ca²⁺ (0.6–2 mM) in the medium. After transient smoothing of the pH bands, some alkaline peaks reemerged at slightly shifted positions in media with low Ca²⁺ concentrations, while at high Ca²⁺ concentrations, the alkaline spots reappeared exactly at their initial positions. This Ca²⁺ dependency has been revealed by both digital imaging and pH microelectrodes. The stabilizing effect of external Ca²⁺ on the locations of recovering alkaline peaks is supposedly due to formation of a physically heterogeneous environment around the cell owing to precipitation of CaCO₃ in the alkaline zones at high Ca²⁺ during illumination. The elevation of local pH by dissolving CaCO₃ facilitates the reappearance of alkaline spots at their initial locations after temporal suppression caused by cell excitation. At low Ca²⁺ concentrations, when the solubility product of CaCO₃ is not attained, the alkaline peaks are not stabilized by CaCO₃ dissolution and may appear at random locations.