title: Monovalent cation permeabilities of the potassium systems in the crab giant axon.
abstract: Permeability ratios for pairs of monovalent cations permeating the two potassium systems proposed for the giant axon of the crab Carcinus maenas (M.E. Quinta-Ferreira, E. Rojas & N. Arispe, J. Membrane Biol. 66:171-181, 1982b) were estimated from measurements of the reversal potential of the currents under voltage-clamp conditions. With K+ inside the axon, permeability ratios from the reversal potential of the currents through the late channel are: PRb/PK = 0.9, PNH4/PK less than 0.2 and PCS/PK = 0.18. With CS+ inside the ratios are: PK/PCS = 8.7, PRb/PCS = 7.1 and PNH4/PCS = 2.4. The analysis of the inward currents carried by Rb+ or NH+4 showed similar reversal potentials for the early transient component and the late sustained component. Whence, the sequence of permeabilities for the two types of potassium channels is: PK greater than PRb greater than PNH4 greater than PNa = PCS. The time constants for the activation of the two components recorded either in K-, Rb-, or NH4-artificial seawater are twice as large as the corresponding time constants measured in Na-artificial seawater.
authors.forename: M E
authors.initials: ME
authors.lastname: Quinta-Ferreira
authors.forename: B
authors.initials: B
authors.lastname: Soria
authors.forename: E
authors.initials: E
authors.lastname: Rojas
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000378:metabolism*; D003386:Brachyura; D002412:Cations; D002463:Cell Membrane Permeability; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism
chemical_list: D002412:Cations; D007473:Ion Channels; D000641:Ammonia; D012413:Rubidium; D011188:Potassium