The ATP deficit from the metabolic switch disables the ion pumps that maintain the cardiomyocyte's electrochemical gradients. The Na+/K+-ATPase, which normally exports three sodium ions for every two potassium ions imported, fails first because it consumes a large share of the cell's ATP. Sodium accumulates inside the cell, and the sodium gradient that drives the Na+/Ca2+ exchanger weakens, so calcium is no longer effectively extruded. Calcium also leaks from the sarcoplasmic reticulum as its ATP-dependent reuptake fails. The rising cytosolic calcium has two consequences. First, it activates calcium-dependent proteases and phospholipases that begin to degrade cell structures. Second, and more immediately, it disrupts the normal contraction-relaxation cycle: the myofilaments become locked in a partially activated state, and without ATP for cross-bridge cycling and calcium reuptake, the cell cannot relax. Contraction fails within seconds of ischemia, and sustained calcium elevation can produce ischemic contracture, a rigid, shortened state. This entire sequence is reversible if flow is restored before the cell crosses the threshold into irreversible injury.
Learn MotionThe Pathophysiology of Myocardial Infarction: From Coronary Occlusion to Clinical Consequence
Ischemia: Metabolic and Functional Consequences of Oxygen Deprivation
From ATP depletion to ion pump failure, calcium overload, and contractile failure
2 / 3
Follow the cascade from ATP loss to pump failure. The Na+/K+-ATPase normally exports three sodium ions for every two potassium ions it imports, and it consumes a large share of the cell's ATP. When ATP falls, this pump fails first, so sodium accumulates inside. That weakens the sodium gradient that drives the Na+/Ca2+ exchanger, so calcium is no longer effectively extruded. At the same time, the sarcoplasmic reticulum can't reuptake calcium because that also requires ATP. Cytosolic calcium rises. Watch what that does: calcium activates proteases and phospholipases that begin degrading cell structures, and it disrupts the contraction-relaxation cycle. Without ATP for cross-bridge cycling and calcium reuptake, the myofilaments stay partially activated and the cell cannot relax. Contraction fails within seconds. If flow is restored before the cell crosses the threshold into irreversible injury, this whole sequence can reverse.
0:00 / 0:00