Investigation of the alpha(1)-glycine receptor channel-opening kinetics in the submillisecond time domain.
The activation and desensitization kinetics of the human alpha(1)-homooligomeric glycine receptor, which was transiently expressed in HEK 293 cells, were studied with a 100-microseconds time resolution to determine the rate and equilibrium constants of individual receptor reaction steps. Concentration jumps of the activating ligands glycine and beta-alanine were initiated by photolysis of caged, inactive precursors and were followed by neurotransmitter binding, receptor-channel opening, and receptor desensitization steps that were separated along the time axis. Analysis of the ligand concentration-dependence of these processes allows the determination of 1) the rate constants of glycine binding, k(+1) approximately 10(7) M(-1) s(-1), and dissociation, k(-1) = 1900 s(-1); 2) the rates of receptor-channel opening, k(op) = 2200 s(-1), and closing, k(cl) = 38 s(-1); 3) the receptor desensitization rate, alpha = 0.45 s(-1); 4) the number of occupied ligand binding sites necessary for receptor-channel activation and desensitization, n >/= 3; and 5) the maximum receptor-channel open probability, p(0) > 0.95. The kinetics of receptor-channel activation are insensitive to the transmembrane potential. A general model for glycine receptor activation explaining the experimental data consists of a sequential mechanism based on rapid ligand-binding steps preceding a rate-limiting receptor-channel opening reaction and slow receptor desensitization.
Grewer
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Max-Planck-Institut for Biophysics, D-60596 Frankfurt, Germany. grewer@kennedy.biophys.mpg.de
D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D002460:Cell Line; D004563:Electrochemistry; D005998:Glycine / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008564:Membrane Potentials; D018009:Receptors, Glycine / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015091:beta-Alanine / Q000378:metabolism
D008024:Ligands; D018009:Receptors, Glycine; D011994:Recombinant Proteins; D015091:beta-Alanine; D005998:Glycine