Title: Ionic Mechanism of Mechano-perception in Characeae

Characean internodal cells generate receptor potential in response to mechanical stimuli. We studied responses of internodal cells upon long-lasting stimulus and the results were as follows. (1) The cell generated receptor potential at both moments of compression and decompression. (2) The receptor potential (∆Em) was significantly larger at the moment of decompression than at the compression. (3) The longer the duration of stimulus, the larger the magnitude of ∆Em at the moment of decompression was. (4) Aequorin studies revealed that the increase in [Ca2+]c (∆[Ca 2+]c) took place at both moments. (5) The amplitude of ∆[Ca2+]c was larger at the moment of decompression than at the compression, as well as the case in ∆Em. It was suggested that the amplitude of the receptor potential had tight correlation with degree of membrane deformation. We discussed the ionic mechanism of mechano-perception under long-lasting stimulus in relation to mechanosensitive activation of Ca channels at the plasma membrane.