Abstract
Some epithelial nonselective cation channels although in an open conformation are impermeable because they are blocked by extracellular Ca2+ ions. Such a channel is present in the apical membrane of the ectodermal cells of the chick gastrula. This single-channel study shows that protonation of a site located inside the pore of this embryonic channel reduces the Ca2+ block thus allowing Na+ to pass. The apparent pK for Ca2+ at −50 mV shifts from 5.7 at pH 7.4 to 3.5 at pH 4.5. Unexpectedly, the change in Ca2+ affinity does not originate from a destabilization of the binding but comes from a large reduction of the association rate.
References
Bell RP (1973) The Proton in Chemistry. Cornell Univ Pres, Ithaca, ed. 2
Bevan S, Geppetti P (1994) Protons: small stimulants of capsaicin-sensitive sensory nerves. Trends Neurosci 17:508–512
Garty H, Benos DJ (1988) Characteristics and regulatory mechanisms of the amiloride-blockable Na+ channel. Physiol Rev 68:309–373
Heinemann SH, Sigworth FJ (1991) Open channel noise. VI. Analysis of amplitude histograms to determine rapid kinetic parameters. Biophys J 60:577–587
Li J, Prod'hom B, Kucera P (1994) Cation channel blocked by extracellular Ca2+ in the apical membrane of the chick embryonic ectoderm. Pflügers Arch 429:183–192
Ogden D, Colqhoun D (1985) Ion channel block by acetylcholine, carbachol and suberyldicholine at the frog neuromuscular junction. Proc R Soc Lond [B] 225:329–355
Root MJ, MacKinnon R (1994) Two identical noninteracting sites in an ion channel revealed by proton transfer. Science 265:1852–1856
Van Driessche W, Zeiske W (1985) Ca2+-sensitive, spontaneously fluctuating, cation channels in the apical membrane of the adult frog skin epithelium. Pflügers Arch 405:250–259
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Sabovcik, R., Li, J., Kucera, P. et al. Extracellular protons modulate the Ca2+ block of a Ca2+-blockable monovalent cation channel in chick embryo. Pflugers Arch. 430, 599–601 (1995). https://doi.org/10.1007/BF00373900
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DOI: https://doi.org/10.1007/BF00373900