One prediction of a multi-ion pore is that its conductance should reach a maximum and then begin to decrease as the concentration of permeant ion is raised equally on both sides of the membrane. A conductance maximum has been observed at the single-channel level in gramicidin and in a Ca(2+)-activated K+ channel at extremely high ion concentration (> 1,000 mM) (Hladky, S. B., and D. A. Haydon. 1972. Biochimica et Biophysica Acta. 274:294-312; Eisenmam, G., J. Sandblom, and E. Neher. 1977. In Metal Ligand Interaction in Organic Chemistry and Biochemistry. 1-36; Finkelstein, P., and O. S. Andersen. 1981. Journal of Membrane Biology. 59:155-171; Villarroel, A., O. Alvarez, and G. Eisenman. 1988. Biophysical Journal. 53:259a. [Abstr.]). In the present study we examine the conductance-concentration relationship in an inward-rectifier K+ channel, ROMK1. Single channels, expressed in Xenopus oocytes, were studied using inside-out patch recording in the absence of internal Mg2+ to eliminate blockade of outward current. Potassium, at equal concentrations on both sides of the membrane, was varied from 10 to 1,000 mM. As K+ was raised from 10 mM, the conductance increased steeply and reached a maximum value (39 pS) at 300 mM. The single-channel conductance then became progressively smaller as K+ was raised beyond 300 mM. At 1000 mM K+, the conductance was reduced to approximately 75% of its maximum value. The shape of the conductance-concentration curve observed in the ROMK1 channel implies that it has multiple K(+)-occupied binding sites in its conduction pathway.
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1 September 1994
Article|
September 01 1994
A conductance maximum observed in an inward-rectifier potassium channel.
Z Lu,
Z Lu
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
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R MacKinnon
R MacKinnon
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
Search for other works by this author on:
Z Lu
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
R MacKinnon
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
Online ISSN: 1540-7748
Print ISSN: 0022-1295
J Gen Physiol (1994) 104 (3): 477–486.
Citation
Z Lu, R MacKinnon; A conductance maximum observed in an inward-rectifier potassium channel.. J Gen Physiol 1 September 1994; 104 (3): 477–486. doi: https://doi.org/10.1085/jgp.104.3.477
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