Gillespie Dirk
Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois.
Biophys J. 2025 Jan 21;124(2):245-255. doi: 10.1016/j.bpj.2024.11.3316. Epub 2024 Nov 27.
Ca blinks measure the exit of Ca from the junctional sarcoplasmic reticulum (JSR) in a cardiac myocyte during a Ca spark. Here, the relationship between experimental blink fluorescence measurements and the [Ca] in the JSR is explored using long 3D simulations of diastolic Ca release. For a fast intra-SR Ca-activated fluorophore such as Fluo-5N, we show that a simple mathematical formula relates the two for an ideal blink (i.e., when fluorescence signals come only from the JSR). The formula shows that normalized JSR [Ca] is much lower than the normalized fluorescence and that JSR Ca depletes ∼40-50% more than previously inferred from blink fluorescence measurements. In addition, we show that stray fluorescence signals (e.g., from other parts of the sarcoplasmic reticulum network) can mask even deeper Ca depletion. Overall, the simulations show that strong JSR Ca depletion such as that seen in many simulations is consistent with the relatively moderate fluorescence changes seen in experiments.
钙闪烁测量心肌细胞中钙火花期间钙从连接肌浆网（JSR）的流出。在此，使用舒张期钙释放的长时间三维模拟来探索实验闪烁荧光测量与JSR中[Ca]之间的关系。对于像Fluo-5N这样的快速肌浆网内钙激活荧光团，我们表明，对于理想闪烁（即当荧光信号仅来自JSR时），一个简单的数学公式将两者联系起来。该公式表明，归一化的JSR [Ca]远低于归一化荧光，并且JSR中的钙消耗比先前从闪烁荧光测量推断的多约40 - 50%。此外，我们表明杂散荧光信号（例如来自肌浆网网络其他部分的信号）甚至可以掩盖更深的钙消耗。总体而言，模拟表明，许多模拟中看到的强烈JSR钙消耗与实验中看到的相对适度的荧光变化是一致的。
