Single-file diffusion through the Ca2+-activated K+ channel of human red cells
The ratio between the unidirectional fluxes through the Ca2+-activated K+-specific ion channel of the human red cell membrane has been determined as a function of the driving force (V m -E K ). Net effluxes and42K influxes were determined during an initial period of ∼90 sec on cells which had been depleted of ATP and loaded with Ca. The cells were suspended in buffer-free salt solutions in the presence of 20 μm of the protonophore CCCP, monitoring in this way changes in membrane potential as changes in extracellular pH. (V m -EK) was varied at constantEK by varying the Nernst potential and the conductance of the anion and the conductance of the potassium ion. In another series of experimentsEK was varied by suspending cells in salt solutions with different K+ concentrations. At high extracellular K+ concentrations both of the unidirectional fluxes were determined as42K in- and effluxes in pairs of parallel experiments. Within a range of (V m -EK) of −6 to 90 mV the ratio between the unidirectional fluxes deviated strongly from the values predicted by Ussing's flux ratio equation. The Ca2+-activated K+ channel of the human red cell membrane showed single-file diffusion with a flux ratio exponentn of 2.7. The magnitude ofn was independent of the driving force (V m -EK), independent ofV m and independent of the conductancegK.
Key Wordssingle-file diffusion Ca2+-activated K+ channel human erythrocytes
Unable to display preview. Download preview PDF.
- Ferreira, H.G., Lew, V.L. 1976. Use of ionophore A23187 to measure cytoplasmic Ca buffering and activation of the Ca pump by internal Ca.Nature (London) 259:47–49Google Scholar
- Hamill, O.P. 1981. Potassium channel currents in human red blood cells.J. Physiol. (London) 319:97P-98PGoogle Scholar
- Hodgkin, A.L., Huxley, A.F. 1952. The components of membrane conductance in the giant axon ofLoligo.J. Physiol. (London) 116:449–472Google Scholar
- Hodgkin, A.L., Keynes, R.D. 1955. The potassium permeability of a giant nerve fibre.J. Physiol. (London) 128:61–88Google Scholar
- Hoffman, J.F., Yingst, D.R., Goldinger, J.M., Blum, R.M., Knauf, P.A. 1980. On the mechanism of Ca-dependent K transport in human red blood cells.In: Membrane Transport in Erythrocytes: Alfred Benzon Symp. 14. U.V. Lassen, H.H. Ussing, and J.O. Wieth, editors. pp. 178–195. Munksgaard. CopenhagenGoogle Scholar
- Latorre, R., Miller, C. 1983. Conduction and selectivity in potassium channels.J. Membrane Biol. 71:11–30Google Scholar
- Latorre, R., Vergara, C., Hidalgo, C. 1981. Reconstitution in planar lipid bilayers of a Ca2+-dependent K+-channel from transverse tubule membranes isolated from rabbit skeletal muscle.Proc. Natl. Acad. Sci. USA 79:805–809Google Scholar
- Lew, V.L., Brown, A.M. 1979. Experimental control and assessment of free and bound calcium in the cytoplasm of intact mammalian red cells.In: Detection and Measurement of Free Ca2+ in Cells. C.C. Ashley, and A.K. Campbell editors. pp. 423–432. Elsevier/North-Holland Biomedical, AmsterdamGoogle Scholar
- Meech, R.W., Standen, N.B. 1975. Potassium activation inHelix aspersa neurons under voltage clamp: A component mediated by calcium influx.J. Physiol. (London) 249:211–239Google Scholar
- Spalding, B.C., Senyk, O., Swift, J.G., Horowicz, P. 1981. Unidirectional flux ratio for potassium ions in depolarized frog skeletal muscle.Am. J. Physiol. 241:c68-c75Google Scholar
- Ussing, H.H. 1949. The distinction by means of tracers between active transport and diffusion.Acta Physiol. Scand. 19:43–56Google Scholar