Figure 2.

Interventions that change [Ca²⁺]_SR. (A–F) Representative SEER ratio images of fluorescence of mag-indo-1 trapped inside organelles of a membrane-permeabilized muscle fiber. (G, top) Schematic representation of [Ca²⁺] in perfusing solutions, including the reference (100 nM), a high Ca²⁺ saline (400 nM) and relaxing solution (∼10 nM). Black symbols and lines plot R, SEER ratio averaged over well-stained regions of the image. Gray bars, the frequency of sparks detected in individual line scan images. Red symbols, f, average spark frequency (±SEM) within series of 50 line scan images. Right offset axis, [Ca²⁺] corresponding to R. Identifier: 061004a.