Beilby MJ and Bisson MA

Journal of Membrane Biology: 1999, 171: 63 - 73

Summary
The current-voltage (I/V) profiles of Valonia membranes were measured at a range of external potassium concentrations, [K⁺]_o, from 0.1 to 100 mM.  The conductance-voltage (G/V) characteristics were computed to facilitate resolution of the profile evolution with time. The resistance-voltage (R/V) characteristics were computed to attempt resolution of plasmalemma and tonoplast. Four basic electrophysiological states emerged:
(1) uniform low resistance throughout the clamp p.d. (potential difference) window after the cell impalement.
(2) High resistance at positive clamp p.d. for  [K⁺]_o from 0.1 to 1.0 mM.
(3) High resistance at negative clamp p.d. for  [K⁺]_o of 10 mM (close to natural seawater) and hypertonic solution.
(4) High resistance throughout most of the clamp p.d. window at [K⁺]_o of 100 mM.
The changes between these states were slow, requiring minutes to hours. Our analysis suggests that unlike in most plants, Valonia tonoplast is the dominant membrane with a pump that can be fitted with an enzyme kinetics model. Together with previous evidence from electrophysiology and flux measurements it seems likely that this pump actively transports K⁺ into the vacuole to regulate turgor.