Depletion of polyP prevents Ca²⁺ release from mitochondria in permeabilized myocytes. (A) Original recordings of [Ca²⁺]_m changes in permeabilized X-Rhod-1–loaded myocytes upon stepwise elevation of [Ca²⁺]_em from 0.1 to 0.8 to 2 µM and subsequent return to 0.1 µM in control (black) and PPX-infected cells (gray). The expression of PPX prevented the release of Ca²⁺ from mitochondria during the exposure to 2 µM Ca²⁺. (B) Average values for [Ca²⁺]_m amplitude measured at 5 min of 0.8 (left)- and 2-µM (middle) Ca²⁺ exposure. (C) Average values for Ca²⁺ extrusion upon exposure to 0.1 µM Ca²⁺ (percent decline normalized to [Ca²⁺]_em levels before exposure to 0.1 µM Ca²⁺; right). (D) Original recordings of [Ca²⁺]_m changes in permeabilized Rhod-2–loaded myocytes upon elevation of [Ca²⁺]_em from 0.1 to 2 µM in control (black), PPX-infected cells (dark gray), CsA-treated control cells (medium gray), and CsA-treated, PPX-infected cells (light gray). (E) Average values of Rhod-2 fluorescence decrease at 10 min after exposure to 2 µM Ca²⁺, calculated as a percentage of the initial maximal increase in control, PPX-infected cells, CsA-treated control, and CsA-treated, PPX-infected cells.