Zinc ions block H+/OH- channels in Chara australis.

摘要

Chara australis cells exposed to media of pH 10 and above exhibit high conductance, arising from the opening of H+/OH- channels in the plasma membrane. This high conductance can be totally inhibited by 1.0 mm ZnCl₂ and restored by 0.5 mm 2-mercaptoethanol (ME). Important for carbon fixation, H+/OH- channels play a key role in cell pH banding. Banding was also shown to be abolished by 1.0 mm ZnCl₂ and restored in some cells by ME. The proton pump is also involved in banding, but was little affected by ZnCl₂ over the periods needed for the inhibition of H+/OH- channels. Previously, we postulated that H+/OH- channels open transiently at the onset of saline stress in salt-sensitive C. australis, causing membrane potential difference (PD) noise; and remain open in latter stages of saline stress, contributing to cell deterioration. ZnCl₂ totally inhibited the saline noise and the upwardly concave I/V characteristics associated with the putative H+/OH- currents. Again, ME reversed both these effects. We discuss the mode of action of zinc ions and ME with reference to animal voltage-gated H+ channels and water channels.