Summary
Permeability ratios for pairs of monovalent cations permeating the two potassium systems proposed for the giant axon of the crabCarcinus 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:P Rb/P K=0.9,\(P_{NH_4 } \)/P K<0.2 andP Cs/P K=0.18. With Cs+ inside the ratios are:P K/P Cs=8.7,P Rb/P Cs=7.1 and\(P_{NH_4 } \)/P Cs=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:P K>P Rb>\(P_{NH_4 } \)>P Na=P Cs. 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.
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Quinta-Ferreira, M.E., Soria, B. & Rojas, E. Monovalent cation permeabilities of the potassium systems in the crab giant axon. J. Membrain Biol. 84, 117–126 (1985). https://doi.org/10.1007/BF01872209
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DOI: https://doi.org/10.1007/BF01872209