Fig. 8.

Ryr1^D/D muscle fibers exhibit pronounced summation of the Ca²⁺ transient during repetitive stimulation. A: Fluo-4 transient responses to single AP stimuli followed by a 100-Hz train of APs show reduced amplitude of Ca²⁺ twitch and tetanic transients in mutant fibers. B: traces from A normalized to initial transient amplitude to demonstrate greater summation of the Ca²⁺ transient during repetitive stimulation of mutant fibers when compared with controls. C: quantification of Ca²⁺ transient summation from B, calculated as the ratio of the amplitude of the last Ca²⁺ transient in the train compared with the first. Summation was increased approximately twofold in the mutant fibers. *P < 0.01.