Excitation-revealed changes in cytoplasmic Cl⁻ concentration in “Cl⁻-starved”Chara cells

Summary

The changes in the cytoplasmic Cl⁻ concentration, [Cl⁻] _c , are monitored at the time of withdrawal (starvation) and subsequent replacement of Cl⁻ in the outside medium. The measurement technique exploits the involvement of Cl⁻ inChara excitation. The transient clamp current due to Cl⁻,I _Cl, is separated from other excitation transients through Hodgkin-Huxley (HH) equations, which have been adjusted toChara. TheI _Cl amplitude depends on HH parameters, [Cl⁻] _c and the maximum membrane conductance to Cl⁻,$\overline {g_{Cl} }$. The results are discussed in terms of these quantities.I _Cl and$\overline {g_{Cl} }$ were found to fall after 6–10 hr of Cl⁻ starvation, thus supporting the hypothesis that [Cl⁻ _c decreases in Cl⁻-free medium. The best HH fit to “starved” data was obtained with [Cl⁻ _c =3.5mm. The time-course forI _Cl decline is considerably slower than the time-course of the rise of the starvation-stimulated influx. As cells starved for periods longer than 24 hr are re-exposed to Cl⁻, it is revealed that while [Cl⁻] _c remains low during long starvation,$\overline {g_{Cl} }$ increases to values greater than those of the normal cells. Such differences among cells starved for various lengths of time have not been detected previously.