What are positive inotropic agents?

What are positive inotropic agents?

• A. Agents that increase contractility by increasing calcium levels in the sarcoplasm.
• B. Agents that decrease contractility by reducing calcium in the sarcoplasm.
• C. Agents that dilate coronary arteries to improve perfusion.
• D. Agents that slow heart rate to reduce oxygen demand.

Answer: (A)

Positive inotropic agents increase the force of heart contraction by raising intracellular calcium in cardiomyocytes. During systole, calcium enters the cell and is released from the sarcoplasmic reticulum; more cytosolic calcium promotes greater binding of calcium to troponin C, which allows more cross-bridge cycling between actin and myosin, producing a stronger heartbeat. Some drugs boost contractility by increasing calcium entry or release, or by increasing calcium sensitivity, all aiming to enhance the heart’s pumping power. The other described actions don’t directly boost contraction strength: dilating coronary arteries improves blood flow but doesn’t inherently make the heart beat harder, and slowing the heart rate reduces oxygen demand rather than increasing contractile force.

Positive inotropic agents increase the force of heart contraction by raising intracellular calcium in cardiomyocytes. During systole, calcium enters the cell and is released from the sarcoplasmic reticulum; more cytosolic calcium promotes greater binding of calcium to troponin C, which allows more cross-bridge cycling between actin and myosin, producing a stronger heartbeat. Some drugs boost contractility by increasing calcium entry or release, or by increasing calcium sensitivity, all aiming to enhance the heart’s pumping power.

The other described actions don’t directly boost contraction strength: dilating coronary arteries improves blood flow but doesn’t inherently make the heart beat harder, and slowing the heart rate reduces oxygen demand rather than increasing contractile force.