title: Calcium-activated potassium conductance in presynaptic terminals at the crayfish neuromuscular junction.
abstract: Membrane potential changes that typically evoke transmitter release were studied by recording intracellularly from the excitor axon near presynaptic terminals of the crayfish opener neuromuscular junction. Depolarization of the presynaptic terminal with intracellular current pulses activated a conductance that caused a decrease in depolarization during the constant current pulse. This conductance was identified as a calcium-activated potassium conductance, gK(Ca), by its disappearance in a zero-calcium/EGTA medium and its block by cadmium, barium, tetraethylammonium ions, and charybdotoxin. In addition to gK(Ca), a delayed rectifier potassium conductance (gK) is present in or near the presynaptic terminal. Both these potassium conductances are involved in the repolarization of the membrane during a presynaptic action potential.
authors.affiliation: Department of Zoology, College of Pharmacy, University of Texas, Austin 78712.
authors.forename: S
authors.initials: S
authors.lastname: Sivaramakrishnan
authors.forename: G D
authors.initials: GD
authors.lastname: Bittner
authors.forename: M S
authors.initials: MS
authors.lastname: Brodwick
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D003400:Astacoidea / Q000502:physiology*; D001464:Barium / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D018999:Charybdotoxin; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000493:pharmacokinetics*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D012604:Scorpion Venoms / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D000631:Aminopyridines; D015221:Potassium Channels; D012604:Scorpion Venoms; D013757:Tetraethylammonium Compounds; D002104:Cadmium; D018999:Charybdotoxin; D001464:Barium; D013779:Tetrodotoxin; D004533:Egtazic Acid; D011188:Potassium; D002118:Calcium