Figure 2.

Coexpression of either L119C or Y188F with wild-type α7 subunits at varying ratios. (A) The probability for the distribution of mutant subunits based on RNA ratios. Each single subunit within a pentamer is either mutant or wild-type, and if we assume X = probability of being wild-type (actually α7C116S) and Y = probability of being mutant, then 1 = X + Y, and for combinations of five subunits, (X + Y)ⁿ = 1. The expansion of this binomial is X⁵ + 5X⁴Y + 10X³Y² + 10X²Y³ + 5XY⁴ + Y⁵ = 1. We assume that receptors are functionally equivalent regardless of the subunit positions within the pentameric structure. (B) Data traces obtained from oocytes expressing the α7C116S/L119C MTSEA-sensitive mutant and the α7C116S cysteine-null pseudo wild-type at the ratios indicated. For each panel, the traces on the left are the 300-µM ACh control responses obtained before the MTSEA treatment, and the series of traces on the right are the responses to progressively greater concentrations of ACh obtained after the MTSEA treatment. (C) Average net charge values for oocytes expressing the α7C116S/L119C MTSEA-sensitive mutant and α7C116S cysteine-null pseudo wild-type at the ratios indicated after treatment with MTSEA, normalized to the 300-µM ACh control responses before MTSEA treatment. The open circles represent the 300-µM ACh control data obtained before the MTSEA treatment (i.e., the values to which the posttreatment data are normalized). The data plotted are the means ± SEM for at least five oocytes at each of the ratios tested. See Table I for curve fit values.