Short-term silencing of Mfn1 does not alter trains of [Ca²⁺]_c transients and activation of the CSMDH in SM fibers. (A) FDB muscles were cotransfected with mtDsRed and NT or Mfn1siRNA. After 7–10 d, fibers were isolated and loaded with Fura2. mtDsRed-positive fibers that responded to single electric pulses were picked. Fibers were challenged by repetitive tetanic ES. Top: representative [Ca²⁺]_c transients. Bottom bar charts show from left to right: [Ca²⁺]_c levels preES, max amplitude (peaks 1–10), the [Ca²⁺]_c transient amplitude decay for the time period indicated by brackets above the representative traces (([mean peaks 1–10] − [mean peaks 30–40])/[mean peaks 1–10] × 100), and irregularity in amplitude of the [Ca²⁺]_c transients (max − min)/max, among peaks 1–100 (n ≥ 4 rats, the number of fibers is shown in the bar charts). (B) FDB muscles were cotransfected with RCaMP and NT or Mfn1siRNA. After 7 d, fibers were isolated and RCaMP-positive ones that responded to single electric pulses were picked for recording [Ca²⁺]_c and NAD(P)H transients during repetitive tetanic ES. The left graph shows a representative example of [Ca²⁺]_c transients (black) and NAD(P)H (blue) of an NTsiRNA fiber. The arrow indicates 5 µM Rotenone addition. Right: mean amplitude of the NADH levels at 30 and 150 s after the beginning of ES (n = 3 rats, the number of fibers is shown in the bar charts).