Myocardcellen

Myocardcellen, or cardiomyocytes, are the primary contractile cells of the heart. They form the myocardium, are elongated and highly branched, and usually contain a single central nucleus (some are binucleated). Their cytoplasm is packed with myofibrils organized into sarcomeres, giving the cells a striated appearance. The intercellular junctions at intercalated discs—desmosomes and fascia adherens for mechanical coupling, and gap junctions for electrical continuity—enable synchronous contraction across the heart muscle.

Their excitation-contraction coupling relies on tightly regulated calcium signaling. An action potential travels along the cell membrane and into T-tubules, triggering Ca2+ entry via L-type channels. This Ca2+ influx triggers calcium release from the sarcoplasmic reticulum through ryanodine receptors, causing myofilament interaction and contraction. Cessation of contraction involves reuptake of Ca2+ by SERCA pumps and extrusion via the sodium–calcium exchanger.

Cardiomyocytes have a high mitochondrial content and rely predominantly on oxidative metabolism, using fatty acids and, to a lesser extent, glucose. They have limited regenerative capacity; after injury, lost cells are typically replaced by scar tissue, contributing to heart failure or arrhythmias.

Differences exist between atrial and ventricular cardiomyocytes in size and gene expression, and the heart’s conduction system (including Purkinje fibers) contains specialized cardiomyocyte‑like cells that coordinate rhythm. Understanding cardiomyocytes is fundamental to studying cardiac physiology, pathophysiology, and therapies for heart disease.