Spermine block of channels resulting from coexpression of a 1:3 or 3:1 molar ratio of S1-WT and S1-ND subunits verifies the global fitting procedure. (A and C) Families of normalized, leak-subtracted ramp I/V curves obtained in patches from oocytes injected with a 1:3 (A) or 3:1 (C) molar ratio of S1-WT+S1-ND cRNA; in the absence of (black lines) or in the presence of 5 (red lines), 20 (cyan lines), 100 (blue lines), and 500 μM (green lines) spermine. (B and D) Families of g_rel/V curves obtained from the I/V curves shown in A and C (solid symbols, color coding as in A and C). Families of solid black lines represent global fits to the ensembles of four g_rel/V curves assuming random coassembly, but allowing for only a single free parameter (p). All other parameters were fixed to the values shown in Table I. Obtained fit parameters were p = 0.28 in B and p = 0.76 in D.