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A feature of the current-voltage (I/V) and conductance-voltage (G/V) characteristics is described, which can be attributed to the action of the proton pump at theChara plasmalemma. The study of pH dependence in the range 4.5 to 11.0 and exposure to metabolic inhibitors confirm the pump involvement. A model describing kinetics of H+-extruding ATPase (Hansen,(More)
The plant action potential (AP) has been studied for more than half a century. The experimental system was provided mainly by the large charophyte cells, which allowed insertion of early large electrodes, manipulation of cell compartments, and inside and outside media. These early experiments were inspired by the Hodgkin and Huxley (HH) work on the squid(More)
The high pH state of Chara plasmalemma (Bisson, M.A., Walker, N.A. 1980. J. Membrane Biol. 56:1–7) was investigated to obtain detailed current-voltage (I/V) and conductance-voltage (G/V) characteristics in the pH range 7.5 to 12. The resting conductance started to increase at a pH as low as 8.5, doubling at pH 9.5, but the most notable increases occurred(More)
It is generally agreed that solute transport across theChara plasma membrane is energized by a proton electrochemical gradient maintained by an H+-extruding ATPase. Nonetheless, as deduced from steady-state current-voltage (I-V) measurements, the kinetic and thermodynamic constraints on H+-ATPase function remain in dispute. Uncertainties necessarily(More)
The current-voltage (I/V) technique was employed to investigate the different electrophysiological states of theChara plasmalemma and their interaction under a range of conditions. In K+ state the membrane became very permeable (conductances >20 S m 2) as [K+]0 increased to 10mm. As the cells were then easily damaged by the voltage-clamp procedures, it was(More)
  • M. J. Beilby, B. N. Beilby
  • 2006
A computer-controlled apparatus is described, which combines the two powerful methods of voltage-clamping and admittance measurement. The 5-Hz admittance ofChara plasmalemma is obtained for transmembrane PD from −400 mV to 0. DC conductance is also measured by the bipolar staircase method. Both the DC and 5-Hz conductances at steady state display a central(More)
The electrophysiological properties of cytoplasm-rich fragments (single membrane samples) prepared from internodal cells of Chara corallina were explored in conjunction with K(+)-sensitive microelectrode and current-voltage (I-V) measurements. This system eliminated the problem of the inaccessible cytoplasmic layer, while preserving many of the electrical(More)
  • N. A. Walker, F. A. Smith, M. J. Beilby
  • 2005
We have previously reported that inward positive current flows across the plasmalemma of voltage-clampedChara cells when ammonia or methylamine is added to the medium. This is attributed to (inward) uniport of the cation. We have measured the stoichiometric ratio of the quantity of methylamine transported to the quantity of positive charge transported. We(More)
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(More)
The current-voltage (I/V) and conductance-voltage (G/ V) characteristics were recorded for intact and perfused (tonoplast-free) cells ofNitellopsis 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(More)