Figure 4.
Actions of the 35-residue β1a peptide on RyR1 channels in the presence of 10 μM cis Ca2+. (A–C) Average values measured over 180 s before and after cytoplasmic addition of the β1a peptide. (A) The relative PO (log rel PO) is the average of the difference between log10 of PO in the presence of β1a C-tail peptide (logPOP) and log10 of control PO (logPOC) for each channel. (B) The relative mean open time (log rel TO) is logTOP-logTOC. (C) The relative mean closed time (log rel TC) is logTCP-logTcC. N = 4–6 experiments for each bin in A–C. Asterisks indicate significant changes from control induced by the peptide. The broken lines indicate a significant difference between each bin under the horizontal bracket and data at the far end of the line. In A, log rel PO with 1–500 nM peptide is significantly different from log rel PO with 0.01 and 0.1 nM peptide. In B, log rel TO with 0.01 nM peptide is significantly greater than log rel TO with 1, 50, and 100 nM peptide. In C, log rel TC with 1–500 nM peptide is significantly less than log rel TC with 0.1 nM peptide, and 10–100 nM is significantly less than 0.01 nM peptide. (D and E) Least-squares fit of a standard Hill equation to the average PO expressed as average POB/POC (open circles for β1a subunit) or POP/POC (solid circles for β1a peptide), calculated for individual channels in the absence (D) and presence (E) of ATP. The fit parameters are given in the text.