Biophys J, August 1999, p. 727-738, Vol. 77, No. 2

Investigation of the ₁-Glycine Receptor Channel-Opening Kinetics in the Submillisecond Time Domain

Max-Planck-Institut for Biophysics, D-60596 Frankfurt, Germany

The activation and desensitization kinetics of the human ₁-homooligomeric glycine receptor, which was transiently expressed in HEK 293 cells, were studied with a 100-µs time resolution to determine the rate and equilibrium constants of individual receptor reaction steps. Concentration jumps of the activating ligands glycine and -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 ~10⁷ M¹ s¹, and dissociation, k₁ = 1900 s¹; 2) the rates of receptor-channel opening, k_op = 2200 s¹, and closing, k_cl = 38 s¹; 3) the receptor desensitization rate,  = 0.45 s¹; 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, p₀ > 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.

Biophys J, August 1999, p. 727-738, Vol. 77, No. 2
© 1999 by the Biophysical Society   0006-3495/99/08/727/12  $2.00

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