Mechanosensitive ion channels in Chara: Influence of water channel inhibitors, HgCl2 and ZnCl2, on generation of receptor potential

Characean internodal cells generate receptor potential (Delta E-m) in response to mechanical stimuli. Upon a long-lasting stimulus, the cells generated Delta E-m at the moment of both compression and decompression, and the amplitude of Delta E-m at the moment of decompression, (Delta E-m)(E), was larger than that at compression. The long-lasting stimulus caused a membrane deformation (Delta D-m) having two components, a rapid one, (Delta D-m)(rapid), at the moment of compression and a slower one, (Delta D-m)(slow), during the long-lasting compression. We assumed that (Delta D (m))(slow) might have some causal relation with the larger Delta E-m at (Delta E-m)(E). We treated internodal cells with either HgCl2 or ZnCl2, water channel inhibitors, to decrease (Delta D-m)(slow). Both inhibitors attenuated (Delta D-m)(slow) during compression. Cells treated with HgCl2 generated smaller (Delta E-m)(E) compared to nontreated cells. On the other hand, cells treated with ZnCl2 never attenuated (Delta E-m)(E) but, rather, amplified it. Thus, the amplitude of (Delta D-m)(slow) did not always show tight correlation with the amplitude of (Delta E-m)(E). Furthermore, when a constant deformation was applied to an internodal cell in a medium with higher or lower osmotic value, a cell having higher turgor always showed a larger (Delta E-m)(E). Thus, we concluded that changes in tension at the membrane may be the most important factor to induce activation of mechanosensitive Ca2+ channel.