The current-voltage (I/V) and conductance-voltage (G/ V) characteristics were recorded for intact and perfused (tonoplast-free) cells of Nitellopsis obtusa. In the pH0 range 5 to 8, the I/V profile was sigmoidal and the G/V profile exhibited a maximum - these characteristics are attributed to the proton pump at the plasmalemma. The pH0 dependence in this range was very similar to that found in Chara corallina. At very alkaline pH0 (11.0) the high conductance due to H+/OH- channels was observed in intact cells but not in perfused cells. Young plants of Nitellopsis did not display bands of calcification, but did exhibit pH banding patterns in petri dishes. The pH bands were less than 5mm wide. The excitation transients in intact cells featured two peaks near the excitation threshold, but more peaks could be observed in the p.d. (potential difference) range -90 to -60 mV. The amplitude of the transients was strongly inhibited at pH0 11.0. In the perfused cells the currents lacked complete inhibition at some p.d. levels, but still exhibited one or two peaks. At high pH0 this lack of inactivation was accentuated. The addition of 5 mM TEA to the outside medium abolished the excitation transients in perfused cells.
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