FIGURE 2.

Uncaging of IP₃ elicits additional Ca²⁺ sparks following osmotic stress in skeletal muscle. a, exposure of FDB fibers with UV laser did not induce changes in cytosolic Ca²⁺ at resting condition (top panel, n = 10 fibers). Fibers loaded with ciIP₃/PM did not show localized Ca²⁺ sparks following UV flash photo-uncaging at resting condition (middle panel, n = 30 fibers). Fibers pretreated with osmotic stress showed significant elevation of Ca²⁺ sparks following photo-uncaging of ciIP₃/PM. (bottom panel, n = 35 fibers); the line scan image was conducted at 7 min after exposure to osmotic stress. b, quantification of Ca²⁺ spark frequency before and after photo-uncaging of IP₃ (calculated from the experiments shown in the bottom panel of a (n = 20 fibers). c, statistical analysis of the amplitude of Ca²⁺ sparks before and after photo-uncaging of IP₃. These analyses were conducted on the first 20 s following photo-uncaging. Results are presented as mean ± S.E.