Studies on mechano-perception in Characeae: Effects of external Ca2+ and Cl-

The effects of modification of extracellular concentrations of Ca2+ and Cl- on mechano-perception were studied in internodal cells of Chara corallina. Cells were stimulated by dropping a piece of glass tubing on them, and the resulting receptor potentials and action potentials were analyzed. When the Ca2+ concentration was extremely lowered by adding EGTA, the amplitudes of both receptor potentials and action potentials were attenuated, suggesting the involvement of Ca2+ channels. However, the possibility remained that attenuation of the amplitude of the receptor potential was caused by modification of membrane characteristics by extreme lowering of [Ca2+](0). When the plasma membrane was depolarized to about 0 mV by adding 100 mM KCI, responses in the negative direction were induced upon mechanical stimulation. When the plasma membrane was depolarized by adding 50 mM K2SO4, responses in the positive direction were induced. Thus, Cl- channels may be involved in responses induced by mechanical stimulation under K+-induced depolarization.