FIG. 4.

4-OH-PCB95 (4-OH) and 5-OH-PCB95 (5-OH) differentially alter RyR1 single channel gating activity. Current gating activities of RyR1 single channels reconstituted in BLM before and after exposure to 10 µM 5-OH-PCB95 (5-OH) or 4-OH-PCB95 (4-OH) were recorded in the presence of 50 µM cis (cytoplasmic side) Ca²⁺ at a holding potential of −40 mV (applied to the trans [luminal side] of the channel as described in Materials and Methods section). A, Open probability (p _o) diary plot that depicts the continuous time course of po changes before (Stage I) and after PCB addition (Stages II, III, and IV) to the cis side of the RyR1 channel (left panel). Right panel summarizes the composition of the cytoplasmic Ca²⁺ and PCB concentrations used in the experimental protocol. B, Data were sampled in 2 s epochs and taken at 8–30 s intervals to calculate p _o, mean open dwell time (t _o, ms), and mean closed dwell time (t _c, ms) to obtain summary table containing mean values of channel gating parameters at each stages: stage I, Control basal channel activity, and after OH-PCB addition stages II, III, and IV. C and D, Representative channel current traces before and after exposure to OH-PCB taken from each time course stage (I–IV). The arrows with “O” and “C” indicate the current amplitudes of the channel at fully open and closed states, respectively. Consistent responses under the identical recording conditions were observed in n = 6 and n = 3 independent BLM measurements for 5-OH and 4-OH, respectively. Statistical analysis results are indicated as *p < .05; **p < .01; ***p < .001, between control (basal channel activity—Stage I) and after addition of PCB at Stage II through IV. Abbreviations: BLM, bilayer lipid membrane; PCB, polychlorinated biphenyl.