Figure 2.

Cytosolic Ca²⁺ transients in single isolated FDB muscle fibers of WT and PV^−/− mice

(A) [Ca²⁺]_cyt determined with Fura-2 AM (ratio 360/380 nm) in the basal resting condition and at the peak of the transient in WT and PV^−/− single FDB fibers with electrical stimulation at 0.5 Hz. n ≥ 38.

(B) Representative traces of the experiment. The arrow indicates stimulation.

(C) Time to the Ca²⁺ transient peak.

(D) Half-time of the decay of the Ca²⁺ transient.

(E and F) Representative traces of [Ca²⁺]_cyt transients in WT and PV^−/− FDB fibers induced by tetanic stimulation at 60 Hz (2 s) with Fura-2 AM (ratio 360/380 nm). Note that the stimulation frequency is not sufficient for complete fusion. The arrows indicate the beginning and the end of the tetanic stimulation. Segment G, decay from first to last peak; arrow H, dip at the end of relaxation.

(G) Decay of [Ca²⁺]_cyt expressed as the ratio of the last peak to the first. n ≥ 15.

(H) Decay of the basal [Ca²⁺]_cyt 200 ms after the last electrical pulse expressed as the ratio to basal [Ca²⁺] before the start of the stimulation. n ≥ 15.

(I and J) Resting [Ca²⁺]_cyt (I) and peak cytosolic Ca²⁺ transients (J) in response to 10 mM caffeine in WT and PV^−/− FDB muscle fibers determined with Fura-2 AM (ratio 340/380 nm). n ≥ 43.

(K) Representative traces of the experiment as in (I) and (J).

(L and M) Resting [Ca²⁺]_cyt (L) and peak cytosolic Ca²⁺ transients (M) in FDB fibers electroporated with either shLUC or shPV determined with Fura-2 AM (ratio 340/380 nm). n ≥ 43.

(N) Representative traces of the experiment as in (L) and (M).

(O and P) Resting [Ca²⁺]_cyt (O) and peak cytosolic Ca²⁺ transients (P) in FDB fibers electroporated with either mCherry or PV-P2A-mCherry plasmids for 7 days determined as in (L) and (M). n ≥ 28.

(Q) Representative traces of the experiment as in (O) and (P).

Data are expressed as mean ± SEM. For data analysis, a two-tailed, unpaired Student’s t test was performed. ^∗p < 0.05; ^∗∗p < 0.01; ^∗∗∗p < 0.001.

Note that the Fura-2 data were collected with two different set-ups. (A–H) Ionoptix setup (ratio 360/380) with 1-kHz sampling rate; (I–Q) Crisel setup (ratio 340/380) with 20 Hz sampling.