Divalent cation modulation of the ionic permeability of the synaptosomal plasma membrane.
Synaptosomes from guinea-pig cerebral cortex reveal two distinct Na+ permeabilities when divalent cations are removed from the incubation. In the presence of Mg2+, Ca2+ chelation by EGTA causes a partial activation of a voltage-dependent tetrodotoxin-sensitive pathway, manifested as a ouabain-sensitive respiratory increase, a partial depolarization of the plasma membrane, and a lowered gradient of gamma-amino[14C]butyrate. In addition there is a hyperpolarization of the mitochondrial membrane potential. When Mg2+ is omitted from the incubation, Ca2+ chelation induces a substantially larger permeability which is only partially sensitive to tetrodotoxin. The tetrodotoxin-insensitive component is not associated with a non-specific permeabilization of the plasma membrane and may be reversed by either Mg2+ or Ca2+.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent; D002463:Cell Membrane Permeability / Q000187:drug effects*; D002540:Cerebral Cortex / Q000648:ultrastructure*; D004533:Egtazic Acid / Q000494:pharmacology; D006168:Guinea Pigs; D007473:Ion Channels / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009861:Onium Compounds / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013574:Synaptosomes / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D002413:Cations, Divalent; D007473:Ion Channels; D009861:Onium Compounds; D009943:Organophosphorus Compounds; D013779:Tetrodotoxin; D004533:Egtazic Acid; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D008274:Magnesium; D002118:Calcium; C013289:tetraphenylphosphonium