Figure 5.

The negative modulation of BTP2 on SR Ca²⁺ release requires t-system integrity. (A) Effect of 10 µM BTP2 on spatially averaged SR fluo-5N (F5N) signal (thin lines represent individual traces, and thick line represent the average of the individuals) on fibers with (green) and without (red) a functional t-system. (B) Mean ± SD of ΔF5N signal after BTP2 treatment. Two-tailed unpaired t test showed significant difference between intact t-system versus disrupted t-system (**, P < 0.005). (C) Selected, simultaneous confocal images of a fiber partially exposed extracellularly to F5N + 10 µM BTP2 and bathed in a solution with rhod-2, in bathing solutions with 1 mM Mg²⁺ (t = 0 s) and 0.4 mM Mg²⁺ (t = 41 s). The red and green dashed squares indicate the ROI exposed to and free of BTP2, respectively. (D) Spatially averaged rhod-2 cytoplasmic fluorescence in an ROI with BTP2 (red) and an ROI without BTP2 (green) over time. (E) Mean ± SD of Ca²⁺ transient amplitudes induced by [Mg²⁺] decrease under the two conditions (n = 5). Dotted lines between the red and green bars indicate data points obtained on the same fiber during the same Ca²⁺ release event. Two-tailed paired t test revealed no significant differences between ROI1 (+BTP2) versus ROI2 (−BTP2). a.u., arbitrary units; ns, not significant.