Analysis of the parameters of MHBPI block after alanine substitution of TM10 residues. (A–C) Parameters of block were determined for WT and alanine-substituted ryanodine-modified channels induced by 20 µM MHBPI at a holding potential of 50 mV in symmetrical 210 mM KCl. Data are plotted as mean ± SEM for between five and eight channels. When significant differences occur between the WT parameter and that of the substituted channel, this is indicated by asterisks (*, P < 0.05; **, P < 0.01).