Figure 4.

Ca²⁺ sparks and blinks at decreased [Ca²⁺]_SR. A, Line scan images and corresponding profiles of Ca²⁺ sparks and blinks originating from the same release site under control conditions and at different times following thapsigargin (TG) (10 μmol/L) application. Spark and blink profiles were fitted with a double exponential function (black, blue, orange, and purple lines). B, Relationship between the initial [Ca²⁺]_SR and the [Ca²⁺]_SR at the blink nadir ([Ca²⁺]_{SR, nadir}). Data were obtained from different Ca²⁺ release sites (indicated by different colors) during thapsigargin application and were normalized to the initial SR Ca²⁺ load before thapsigargin application (100%). C, Summary of results shown in B with data grouped into control (100%), intermediate (85% to 95%), and low (70% to 80%) initial [Ca²⁺]_SR level. Initial [Ca²⁺]_SR (SR Ca²⁺ load before release) represented in gray with [Ca²⁺]_SR at the blink nadir shown in black. D, Normalized decay of Ca²⁺ sparks and corresponding recovery of blinks under control conditions (black) and in the presence of 10 μmol/L thapsigargin (orange). The profiles were obtained from exponential fits of experimental traces in A (control and thapsigargin, 5 minutes). *P<0.05.