Monovalent cation permeabilities of the potassium systems in the crab giant axon |
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Authors: | M Emilia Quinta-Ferreira Bernat Soria Eduardo Rojas |
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Institution: | (1) Department of Biophysics, School of Biological Sciences, University of East Anglia, Norwich, England;(2) Laboratory of Cell Biology and Genetics, NIADDK, NIH, 20205 Bethesda, Maryland |
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Abstract: | 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
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
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
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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Keywords: | giant axon potassium channel crab axon K-channel selectivity |
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