Figure 6.

Clustering changes desensitization. (A) Two traces of 10 μM GABA-induced currents were normalized. The line above the traces indicates the time period of GABA application. The holding potential was −60 mV. The decay of the currents was fitted with a single exponential. Diffuse receptors desensitized at a time constant τ = 1 s; clustered receptors had a τ = 2 s. (B) The concentration-dependent rate constant of desensitization. The data points represent the average value from 5 cells with diffuse receptors and 7 cells with clustered receptors. The data were fitted with an equation: 1/τ = α log[GABA] + C, where τ is the time constant for desensitization, [GABA] is the concentration of GABA, α is the rate constant of desensitization, C is the desensitization rate (1/τ) at [GABA] = 1 μM. Both diffuse and clustered receptors had almost same α value (0.57 vs. 0.59 M⁻¹⋅s⁻¹) but different C (0.25 vs. 0 μM). This result means that clustering may change not the concentration-dependent rate constant of desensitization, but the apparent affinity of GABA binding.