Figure 4

The association of glycine receptors with the tubulin-cytoskeleton may influence partial agonist efficacy. (A) Tubulin depolymerization with colchicine decreased both taurine and β-alanine efficacy of α₂β glycine receptors expressed in HEK 293 cells. Cells were treated with 100 μM colchicine or γ-lumicolchicine at 37°C for 30 minutes. The graph shows the partial agonist efficacy as a fraction of the maximal glycine response. For taurine (□), colchicine treatment reduced apparent efficacy from 33 ± 6% in control cells (n = 8) to 13 ± 3% in treated cells (n = 10). γ-lumicolchicine, an inactive analogue of colchicine, had no effect on taurine efficacy (29 ± 9%, n = 5, ** – P < 0.01 from ANOVA). For β-alanine (■), efficacy was reduced from 70 ± 7% in vehicle-treated cells (n = 8) or 67 ± 8% in γ-lumicolchicine-treated cells (n = 5) to 49 ± 6% in cholchicine-treated cells (n = 10, * – P < 0.05, ANOVA). (B) Colchicine treatment does not influence partial agonist efficacy of the GlyRα₂ homomeric channels. Taurine (□) efficacy was 34 ± 15% in control GlyRα₂ cells (n = 4) and was 38 ± 10% in colchicine-treated cells (n = 5, P >> 0.05 t-test). Similarly, β-alanine efficacy was 72 ± 12% and 86 ± 8% in the same control and treated cells, respectively (P >> 0.05, t-test). (C) Colchicine treatment decreases β-alanine efficacy in L-cells expressing GlyRα₂β heteromeric channels (■), but not those expressing GlyRα₂ homomeric channels (□). For the GlyRα₂β channels, colchicine treatment significantly reduced efficacy from 23 ± 2% (n = 7) to 12 ± 3% (n = 3, P < 0.05 t-test). (D) Gephyrin-like immunoreactivity was detected in both cells lines using 20 and 40 μg of whole cell lysate. * – denotes expected gephyrin mobility (approx. 100 kD).