Mechanosensitive Ca²⁺ Channels of Characeae may be Triggered by the Membrane Stretching

Abstract

Receptor potential of characean plants against mechanical stimuli is accounted for by an activation of Cl^- channels at the plasma membrane. We have demonstrated that the first step of receptor potential is an activation of mechanosensitive Ca²⁺ channels, but the mechanism of Ca²⁺ channels activation is unknown. We hypothesized the following two mechanisms (1) membrane deformation triggers the channel activation and (2) the membrane stretching does.
We first compressed the plasma membrane by plasmolysing the cell, then stretched the membrane by deplasmolysing the cell, and the Ca²⁺ channels activation was monitored by measuring light emission from aequorin microinjected into the cell. Transient increase in cytoplasmic level of Ca²⁺ was induced not only by the plasmolysis but also by the deplasmolysis, but the both patterns of the transient were different from each other. We discussed that activation of the mechanosensitive channels is triggered by the membrane stretching.