Kinetics of chloride-bicarbonate exchange across the human red blood cell membrane.
We use a fluorescent probe of [Cl-], 6-methoxy-N-(3-sulfopropyl)quinolinium (SPQ), to study Cl-/HCO-3 exchange in human erythrocyte ghosts in a stopped-flow apparatus at 4 degrees C. The quench constant of SPQ in our Cl-/HCO-3/HPO=4 system at pH 7.4 is 0.065 +/- 0.005 mM-1. The time course of Cl-/HCO-3 exchange does not follow a single exponential function at 4 degrees C and we propose an extended ping-pong model in which slippage is explicitly considered in order to account for this phenomenon. The solution of the system of equations generated by our model is a double exponential function which fits the time course of Cl-/HCO-3 exchange. Our results confirm the predictions of the model concerning the functional dependence of the two rate constants. One rate constant (k1) is independent of medium composition; it is determined by the sum of the two slippage rate constants and its value is 1.04 +/- 0.14 sec-1. The other rate constant (k2) varies inversely with [Cl-]; the regression line is 1/k2 = 18.8 sec - 0.095 mM-1sec [Cl-].
Greco
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FA
The Biophysical Laboratory, Harvard Medical School, Boston, MA 02115, USA.
Solomon
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AK
D017920:Antiporters / Q000097:blood*; D001639:Bicarbonates / Q000097:blood*; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000097:blood*; D004910:Erythrocyte Membrane / Q000378:metabolism*; D005456:Fluorescent Dyes; D006801:Humans; D007700:Kinetics; D011806:Quinolinium Compounds; D013050:Spectrometry, Fluorescence
D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D005456:Fluorescent Dyes; D011806:Quinolinium Compounds; C052335:6-methoxy-N-(3-sulfopropyl)quinolinium