Autonomous Local Area Control over Membrane Transport in Chara Internodal Cells

Internodal cells of Chara were separated with a Plexiglas divider into two segments and the vibrating probe was used to investigate the extracellular current profiles that formed along these two surfaces. Treating one segment of the Chara cell with K⁺ concentrations greater than 2 millimolar caused a dramatic reduction in the extracellular current pattern in this compartment. Concentrations of 5, 10, and 20 millimolar K⁺ were used to establish that a normal current profile could be maintained along the cell surface in the control compartment, whereas the extracellular current profile was strongly reduced along the entire cell surface that was located in the second, high-K⁺ compartment. Simultaneous measurements of the membrane potential in the two segments of the divided Chara cell established that, in the presence of elevated K⁺ concentrations, a longitudinal voltage gradient of up to 60 millivolts was maintained. Experiments in which the pH value in one compartment was either decreased (pH 6.0) or increased (pH 11) gave rise to a reduced extracellular current profile along this segment of the cell, whereas the pattern in the control segment remained unaltered. These results are discussed in terms of the cellular spatial control system that must function to regulate the regions of outward and inward current, and the concept of autonomous local area (domain) control is presented.