Regulation of the fast vacuolar channel by cytosolic and vacuolar potassium.
At resting cytosolic Ca(2)(+), passive K(+) conductance of a higher plant tonoplast is likely dominated by fast vacuolar (FV) channels. This patch-clamp study describes K(+)-sensing behavior of FV channels in Beta vulgaris taproot vacuoles. Variation of K(+) between 10 and 400 mM had little effect on the FV channel conductance, but a pronounced one on the open probability. Shift of the voltage dependence by cytosolic K(+) could be explained by screening of the negative surface charge with a density sigma = 0.25 e(-)/nm(2). Vacuolar K(+) had a specific effect on the FV channel gating at negative potentials without significant effect on closed-open transitions at positive ones. Due to K(+) effects at either membrane side, the potential at which the FV channel has minimal activity was always situated at approximately 50 mV below the potassium equilibrium potential, E(K(+)). At tonoplast potentials below or equal to E(K(+)), the FV channel open probability was almost independent on the cytosolic K(+) but varied in a proportion to the vacuolar K(+). Therefore, the release of K(+) from the vacuole via FV channels could be controlled by the vacuolar K(+) in a feedback manner; the more K(+) is lost the lower will be the transport rate.
Pottosin
Igor I
II
Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, 28047 Colima, Col., México. pottosin@cgic.ucol.mx
Martínez-Estévez
Manuel
M
D027461:Beta vulgaris / Q000187:drug effects* / Q000502:physiology*; D002478:Cells, Cultured; D003600:Cytosol / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000494:pharmacology*; D012680:Sensitivity and Specificity; D014617:Vacuoles / Q000502:physiology
D007473:Ion Channels; D011188:Potassium