title: A new scheme of symbiosis: ligand- and voltage-gated anion channels in plants and animals.
abstract: Anion channels in the plasma membrane of both plant and animal cells participate in a number of important cellular functions such as volume regulation, trans-epithelial transport, stabilization of the membrane potential and excitability. Only very recently attention has turned to the presence of anion channels in higher plant cells. A dominant theme among recent discoveries is the role of Ca2+ in activating or modulating channel current involved in signal transduction. The major anion channel of stomatal guard cell protoplasts is a 32-40 pS channel which is highly selective for anions, in particular NO3-, Cl- and malate. These channels are characterized by a steep voltage dependence. Anion release is elicited upon depolarization and restricted to a narrow voltage span of -100 mV to the reversal potential of anions. During prolonged activation the current slowly inactivates. A rise in cytoplasmic calcium in the presence of nucleotides evokes activation of the anion channels. Following activation they catalyse anion currents 10-20 times higher than in the inactivated state thereby shifting the resting potential of the guard cell from a K(+)-conducting to an anion-conducting state. Patch-clamp studies have also revealed that growth hormones directly affect voltage-dependent activity of the anion channel in a dose-dependent manner. Auxin binding resulted in a shift of the activation potential towards the resting potential. Auxin-dependent gating of the anion channel is side- and hormone-specific. Its action is also channel-specific as K+ channels coexisting in the same membrane patch were insensitive to this ligand.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D003001:Cloning, Molecular; D006133:Growth Substances / Q000494:pharmacology; D015640:Ion Channel Gating; D007473:Ion Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D008024:Ligands; D008564:Membrane Potentials; D009711:Nucleotides / Q000494:pharmacology; D010944:Plants / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D006133:Growth Substances; D007473:Ion Channels; D008024:Ligands; D009711:Nucleotides; D002118:Calcium