Conduction and blocking properties of a predominantly anion-selective channel from human platelet surface membrane reconstituted into planar phospholipid bilayers.
We have investigated the basic properties of a predominantly anion-selective channel derived from highly purified human platelet surface membrane. Single channels have been reconstituted into planar phospholipid bilayers by fusion of membrane vesicles and recorded under voltage-clamp conditions. The channel is found to have the following properties: (i) Channel activity occurs in bursts of openings separated by long closed periods. (ii) The current-voltage relationship is nonlinear. Channel current is seen to rectify, with less current flowing at positive than at negative voltages. Rectification may be due to asymmetric block by HEPES/Tris buffers. In 450 mM KCl, 5 mM HEPES/Tris, pH 7.2, the single channel conductance at -40 mV is approximately 160 pS and at +40 mV is approximately 90 pS. (iii) The conductance-concentration relationship follows a simple saturation curve. Half maximal conductance is achieved at a concentration of approximately 1000 mM KCl, and the curve saturates at a conductance of approximately 500 pS. (iv) Reversal potentials interpreted in terms of the Goldman-Hodgkin-Katz equation indicate a Cl: K permeability ratio of 4:1. (v) The channel accepts all of the halides as well as a number of other anions. The following sequence of relative anion permeabilities (in the presence of K+) is obtained: F- less than acetate- less than gluconate- less than Cl- less than Br- less than I- less than NO3- less tha SCN-.(vi) Cations as large as TEA+ are permeant. (vii) Current through the channel is blocked in the presence of DIDS, SITS and ATP, but not by Zn2+.
Manning
S D
SD
Department of Cardiac Medicine, University of London, United Kingdom.
Williams
A J
AJ
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000838:Anions; D001792:Blood Platelets / Q000648:ultrastructure*; D002412:Cations; D002462:Cell Membrane / Q000502:physiology*; D002463:Cell Membrane Permeability; D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008051:Lipid Bilayers; D008081:Liposomes; D010743:Phospholipids; D011188:Potassium / Q000378:metabolism
D000838:Anions; D002412:Cations; D002712:Chlorides; D007473:Ion Channels; D008051:Lipid Bilayers; D008081:Liposomes; D010743:Phospholipids; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000255:Adenosine Triphosphate; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium