Anion channels in chara corallina tonoplast membrane: calcium dependence and rectification.
Tonoplast K(+) channels of Chara corallina are well characterized but only a few reports mention anion channels, which are likely to play an important role in the tonoplast action potential and osmoregulation of this plant. For experiments internodal cells were isolated. Cytoplasmic droplets were formed in an iso-osmotic bath solution according to a modified procedure. Ion channels with conductances of 48 pS and 170 pS were detected by the patch-clamp technique. In the absence of K(+) in the bath solution the 170 pS channel was not observed at negative pipette potential values. When Cl(-) on either the vacuolar side or the cytoplasmic side was partly replaced with F(-), the reversal potential of the 48 pS channel shifted conform to the Cl(-) equilibrium potential with similar behavior in droplet-attached and excised patch mode. These results showed that the 48 pS channel was a Cl(-) channel. In droplet-attached mode the channel rectified outward current flow, and the slope conductance was smaller. When Chara droplets were formed in a bath solution containing low (10(-8) m) Ca(2+), then no Cl(-) channels could be detected either in droplet-attached or in inside-out patch mode. Channel activity was restored if Ca(2+) was applied to the cytoplasmic side of inside-out patches. Rectification properties in the inside-out patch configuration could be controlled by the holding pipette potential. Holding potential values negative or positive to the calculated reversal potential for Cl(-) ions induced opposite rectification properties. Our results show Ca(2+)-activated Cl(-) channels in the tonoplast of Chara with holding potential dependent rectification.
Berecki
G
G
Center for Phytotechnology RUL/TNO, TNO Department of Plant Biotechnology, Wassenaarseweg 64, 2333 AL, Leiden, The Netherlands.
Varga
Z
Z
Van Iren
F
F
Van Duijn
B
B
D000200:Action Potentials; D000818:Animals; D000838:Anions / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002586:Cesium / Q000378:metabolism; D065101:Chloride Channel Agonists; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D000460:Chlorophyta / Q000166:cytology* / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004553:Electric Conductivity; D005461:Fluorine / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D010940:Plant Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013379:Substrate Specificity; D014617:Vacuoles / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology
D000838:Anions; D065101:Chloride Channel Agonists; D018118:Chloride Channels; D002712:Chlorides; D010940:Plant Proteins; D015221:Potassium Channels; D002586:Cesium; D005461:Fluorine; D012964:Sodium; D015032:Zinc; D002118:Calcium