Abstract.
The current-voltage (I/V) profiles of Ventricaria (formerly 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 better resolution of the profile change with time after exposure to different [K+] o . The resistance-voltage (R/V) characteristics were computed to attempt resolution of plasmalemma and tonoplast. Four basic electrophysiological stages emerged: (1) Uniform low resistance between −60 and +60 mV after the cell impalement. (2) High resistance between +50 and +150 for [K+] o from 0.1 to 1.0 mm and hypotonic media. (3) High resistance between −150 and −20 mV for [K+] o of 10 mm (close to natural seawater) and hypertonic media. (4) High resistance between −150 and +170 mV at [K+] o of 100 mm.
The changes between these states were slow, requiring minutes to hours and sometimes exhibiting spontaneous oscillations of the membrane p.d. (potential difference). Our analysis of the I/V data supports a previous hypothesis, that Ventricaria tonoplast is the more resistive membrane containing a pump, which transports K+ into the vacuole to regulate turgor. We associate state (1) with the plasmalemma conductance being dominant and the K+ pump at the tonoplast short-circuited probably by a K+ channel, state (2) with the K+ pump ``off'' or short-circuited at p.d.s more negative than +50 mV, state (3) with the K+ pump ``on,'' and state (4) with the pump dominant, but affected by high K+. A model for the Ventricaria membrane system is proposed.
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Received: 5 November 1998/Revised: 11 May 1999
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Beilby, M., Bisson, M. Transport Systems of Ventricaria ventricosa: I/V Analysis of Both Membranes in Series as a Function of [K+] o . J. Membrane Biol. 171, 63–73 (1999). https://doi.org/10.1007/s002329900559
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DOI: https://doi.org/10.1007/s002329900559