Fig. 7.

Subunit-specific differences in the recovery from desensitization. A, Paired-pulses of nicotine (10 μm) applied to an oocyte expressing α4β2 receptors at an interpulse interval of 20 min. To account for differences in the relative amount of desensitization in calcium-containing and calcium-free media, we quantified recovery by measuring the fractional increase in the amplitude of the second pulse (I₂) with respect to the amount of desensitization (I₁) induced by a 3 min application of nicotine. B, Plot of the fractional recovery from desensitization at various interpulse intervals in the presence (open circles) or absence (filled circles) of added calcium. C, Histogram of the relative recovery from desensitization for each nAChR subtype in the presence or absence of calcium. The number of experiments for each subtype is indicated inparentheses. The interpulse intervals were 10 min for both α4β4 receptors and α4β2 receptors, 5 min for α3β4 receptors, and 3 min for α3β2 receptors. Individual oocytes expressing α4β2 and α3β2 receptors were measured in both calcium-free and calcium-containing media. Significant differences (p < 0.05) between the results obtained in the two conditions are indicated by the asterisk.