Abstract
Potassium channels are regulated by protons in various ways and, in most cases, acidification results in potassium current reduction. To elucidate the mechanisms of proton-channel interactions we investigated N-terminally truncated Shaker potassium channels (Kv1 channels) expressed in Xenopus oocytes, varying pH at the intracellular and the extracellular face of the membrane. Intracellular acidification resulted in rapid and reversible channel block. The block was half-maximal at pH 6.48, thus even physiological excursions of intracellular pH will have an impact on K+ current. The block displayed only very weak voltage dependence and C-type inactivation and activation were not affected. Extracellular acidification (up to pH 4) did not block the channel, indicating that protons are effectively excluded from the selectivity filter. Channel current, however, was reduced greatly due to marked acceleration of C-type inactivation at low pH. In contrast, inactivation was not affected in the T449V mutant channel, in which C-type inactivation is impaired. The pH effect on inactivation of the wild-type channel had an apparent pK of 4.7, suggesting that protonation of extracellular acidic residues in Kv channels makes them subject to pH regulation.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Baukrowitz T, Yellen G (1996) Two functionally distinct subsites for the binding of internal blockers to the pore of voltage-activated K+ channels. Proc Natl Acad Sci USA 93:13357–13361
Busch AE, Hurst RS, North RA, Adelman JP, Kavanaugh MP (1991) Current inactivation involves a histidine residue in the pore of the rat lymphocyte potassium channel RGK5. Biochem Biophys Res Commun 179:1384–1390
Claydon TW, Boyett MR, Sivaprasadarao A, Ishii K, Owen JM, O'Beire HA, Leach R, Komukai K, Orchard CH (2000) Inhibition of the K+ channel Kv1.4 by acidosis: protonation of an extracellular histidine slows the recovery from N-type inactivation. J Physiol (Lond) 526:253–264
Del Camino D, Yellen G (2001) Tight steric closure at the intracellular activation gate of a voltage-gated K+ channel. Neuron 32:649–656
Deutsch C, Lee SC (1989) Modulation of K+ currents in human lymphocytes by pH. J Physiol (Lond) 413:399–413
Doyle DA, Morais Cabral J, Pfuetzner RA, Kuo A, Gulbis JM, Cohen SL, Chait BT, MacKinnon R (1998) The structure of the potassium channel: molecular basis of K+ conduction and selectivity. Science 280:69–77
Fakler B, Schultz JH, Yang J, Schulte U, Brandle U, Zenner HP, Jan LY, Ruppersberg JP (1996) Identification of a titratable lysine residue that determines sensitivity of kidney potassium channels (ROMK) to intracellular pH. EMBO J 15:4093–4099
Hamill OP, Marty A, Neher E, Sakmann B, Sigworth F (1981) Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pflugers Arch 391:85–100
Heinemann SH (1995) Guide to data acquisition and analysis. In: Sakmann B, Neher E (eds). Single channel recording, 2nd edn. Plenum Press, 53–91
Heinemann SH, Conti F (1992) Non-stationary noise analysis and its application to patch clamp recordings. Methods Enzymol 207:131–148
Hille B (2001) Ion channels of excitable membranes, 3rd edn. Sinauer, Sunderland
Hoshi T, Zagotta WN, Aldrich RW (1990) Biophysical and molecular mechanisms of Shaker potassium channel inactivation. Science 250:533–538
Jäger H, Grissmer S (2001) Regulation of a mammalian Skaker-related potassium channel, hKv1.5, by extracellular potassium and pH. FEBS Lett 488:45–50
Jäger H, Rauer H, Nguyen AN, Aiyar J, Chandy KG, Grissmer S (1998) Regulation of mammalian Shaker-related K+ channels: evidence for non-conducting closed and non-conducting inactivated states. J Physiol (Lond) 506:291–301
Kehl SJ, Eduljee C, Kwan DCH, Zhang S, Fedida DJ (2002) Molecular determinants of the inhibition of human Kv1.5 potassium currents by external protons and Zn2+. J Physiol (Lond) 541:9–24
Loots E, Isacoff EY (1998) Protein rearrangements underlying slow inactivation of the Shaker K+ channel. J Gen Physiol 112:377–389
López-Barneo J, Hoshi T, Heinemann SH, Aldrich RW (1993) Effects of external cations and mutations in the pore region on C-type inactivation of Shaker potassium channels. Receptors Channels 1:61–71
Mannuzzu LM, Moronne MM, Isacoff EY (1996) Direct physical measure of conformational rearrangement underlying potassium channel gating. Science 27:213–216
Melishchuck A, Armstrong CM (2001) Mechanism underlying slow kinetics of the OFF gating current in Shaker potassium channels. Biophys J 80:2167–2175
Pérez-Cornejo P (1999) H+ ion modulation of C-type inactivation of Shaker K+ channels. Pflugers Arch 437:865–870
Pomes R, Roux B (2002) Molecular mechanism of H+ conduction in the single-file water chain of the gramicidin channel. Biophys J 82:2304–2316
Steidl JV, Yool AJ (1999) Differential sensitivity of voltage-gated potassium channels Kv1.5 and Kv1.2 to acidic pH and molecular identification of pH sensor. Mol Pharmacol 55:812–820
Steffan R, Heinemann SH (1997) Error estimates for results of nonstationary noise analysis derived with linear least squares methods. J Neurosci Methods 78:51–63
Acknowledgements
We would like to thank Mark Henteleff, Melanie Hong, and Angela Roßner for technical assistance and Martin Rayner for helpful comments. This study was supported by NIH R01-NS21151 and University of Hawaii bridging funds.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Starkus, J.G., Varga, Z., Schönherr, R. et al. Mechanisms of the inhibition of Shaker potassium channels by protons. Pflugers Arch - Eur J Physiol 447, 44–54 (2003). https://doi.org/10.1007/s00424-003-1121-0
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00424-003-1121-0