The use of Ca‐transient to evaluate Ca2+ utilization by myofilaments in living cardiac muscle

The kinetics of Ca2+ interaction with myofilaments is an important determinant of the preload‐dependent effects on myocardial contractility (the Frank–Starling Mechanism). However, the direct evaluation of this interaction in intact tissue is limited. To overcome this issue, the method of difference curve was proposed, which implements the subtraction of the referent Ca‐transient (measured in non‐stretched muscle) from the Ca‐transients measured at different preloads. This method was tested on the cardiac trabeculae of healthy (CONT) and monocrotaline‐treated rats (MCT), subjected to force–length protocol with simultaneous measurement of isometric twitch and Ca‐transient. The difference curve had two components, C2 and C3, which are distinct in their directions and, as hypothesized, may reflect mainly the kinetics of Ca2+ utilization by and release from myofilaments, respectively. Both the components were quantitatively evaluated by their amplitude, integral magnitude and time‐to‐peak. The C3 component in either CONT or MCT was significantly higher in its amplitude/integral magnitude vs the C2 component, at any preload (P