Which statement reflects the effect of increased intracellular calcium on cardiac contractility?

Which statement reflects the effect of increased intracellular calcium on cardiac contractility?

• A. Increases contractility
• B. Decreases contractility
• C. Decreases automaticity
• D. Shortens the action potential duration

Answer: (A)

When intracellular calcium rises, cardiac contractility increases because calcium binds to troponin C on the thin filament, enabling actin–myosin cross-bridge cycling and producing a stronger contraction. In ventricular cells, calcium entering through L-type channels during the plateau triggers calcium-induced calcium release from the sarcoplasmic reticulum, boosting the cytosolic calcium transient. More calcium bound to troponin C means more cross-bridges form and greater force is generated—positive inotropy. The other options don’t reflect this direct link: increased calcium doesn’t inherently reduce contractility, automaticity is about the heart’s pacemaker activity, and while calcium handling can influence repolarization dynamics, the immediate and primary effect of higher cytosolic calcium in this context is stronger contraction.

When intracellular calcium rises, cardiac contractility increases because calcium binds to troponin C on the thin filament, enabling actin–myosin cross-bridge cycling and producing a stronger contraction. In ventricular cells, calcium entering through L-type channels during the plateau triggers calcium-induced calcium release from the sarcoplasmic reticulum, boosting the cytosolic calcium transient. More calcium bound to troponin C means more cross-bridges form and greater force is generated—positive inotropy. The other options don’t reflect this direct link: increased calcium doesn’t inherently reduce contractility, automaticity is about the heart’s pacemaker activity, and while calcium handling can influence repolarization dynamics, the immediate and primary effect of higher cytosolic calcium in this context is stronger contraction.