Spermine block of channels resulting from coexpression of a 1:1 molar ratio of S1-WT and S2-ND subunits reveals near-random coassembly. (A) Family of normalized, leak-subtracted ramp I/V curves, obtained in a patch from an oocyte injected with a 1:1 molar ratio of S1-WT+S2-ND cRNA; in the absence of (black line), or in the presence of 5 (red line), 20 (cyan line), 100 (blue line), and 500 μM (green line) spermine. (B) Family of g_rel/V curves obtained from the I/V curves shown in (A) (solid symbols, color coding as in A). The family of solid black lines represents a 13-free parameter global fit to the ensemble of the four g_rel/V curves, allowing for nonrandom coassembly. Obtained fit parameters were a₁ = 0.306, a₂ = 0.261, a₃ = 0.244, a₄ = 0.188, K₀₁ = 172 μM, ρ₁ = 2.84, n_H1 = 0.95, K₀₂ = 2.49 mM, ρ₂ = 1.28, n_H2 = 0.95, K₀₃ = 2.82 mM, ρ₃ = 0.78, n_H3 = 0.95. The parameters for components 0 and 4 were fixed to the values shown in Table I. The family of dotted black lines represents the best global fit assuming no coassembly between S1-WT and S2-ND subunits. (C) Visual display of average fit parameters for components i = 0…4. Numbers in the top panel indicate the identities of the components. (D) Average fractional amplitudes a_i (top) and normalized fractional amplitudes (bottom) obtained for components i = 0…4. For normalization, a p value was first calculated using Eq. 10; each a_i value was then divided by the fractional amplitude expected for a binomial distribution generated by that particular p (Eq. 9).