Table 5.
Typical measurements derived from Ca2+ fluorescence signals and the general physiological insight they provide
| Parameter | Description | Physiological Inference |
|---|---|---|
| Time-to-peak (TTP) | The time from initiation of Ca2+ departure (t0) to peak fluorescence | RyR Ca2+ release kinetics |
| Rise time | Duration from 10% to 90% of Cai2+ upstroke | RyR Ca2+ release kinetics |
| Maximum departure velocity | The maximum first derivative (dF/dt)max of the Cai2+ upstroke | RyR Ca2+ release kinetics |
| CaD50, CaD80, CaD90 | The duration from t0 to 50, 80, or 90% of cytosolic Ca2+ extrusion | Duration of cytosolic Ca2+ extrusion |
| T50 | The duration from peak to 50% of cytosolic Ca2+ extrusion | Early extrusion phase, fast Ca2+ extrusion, emphasis on SERCA activity (49) |
| Decay time constant (τFall) | The time required for cytosolic Ca2+ extrusion to reach 1-1/e (∼63.2%) of baseline | Late Ca2+ extrusion phase, slow Ca2+ extrusion, emphasis on NCX activity (49) |
| CaD30/CaD80 | Ratio of early Ca2+ extrusion phase to late Ca2+ extrusion phase | Balance of SERCA and NCX activity (49) |
| Vm/Cai2+ phase chirality | The chirality of the phase plot of the normalized Cai2+ signal vs. the normalized Vm signal | Counterclockwise chirality indicates normal Vm/Cai2+ coupling, and clockwise chirality indicates abnormal Vm/Cai2+ coupling (70) |
| CaD-APD | Difference between Cai2+ transient duration and optical action potential duration | Increasing difference between CaD and APD may lead to DAD (49) |
RyR, ryanodine receptor; SERCA, sarco(endo)plasmic reticulum Ca2+-ATPase; NCX, sodium-calcium exchanger; DAD, delayed afterdepolarization.