Genetically Engineered Models with Alterations in Cardiac Membrane Calcium-Handling Proteins

Regulation of intracellular Ca²⁺ provides a means by which the strength and duration of cardiac muscle contraction is altered on a beat-to-beat basis. Ca²⁺ homeostasis is maintained by proteins of the outer cell membrane or sarcolemma and the sarcoplasmic reticulum, which is the major intracellular Ca²⁺ storage organelle. Recently, genetic engineering techniques designed to induce specific mutations, manipulate expression levels, or change a particular isoform of various membrane Ca²⁺-handling proteins have provided novel approaches in elucidating the physiological role of these gene products in the mammalian heart. This review summarizes findings in murine genetic models with alterations in the expression levels of the sarcolemmal Ca²⁺-ATPase and Na⁺/Ca²⁺ exchanger, which move Ca²⁺ across the cell membrane, and the sarcoplasmic reticulum proteins, which are involved in Ca²⁺ sequestration (Ca²⁺-ATPase and its regulator, phospholamban), Ca²⁺ storage (calsequestrin), and Ca²⁺ release (ryanodine receptor, FK506-binding protein and junctin) during excitation-contraction coupling. Advances in genetic technology, coupled with the development of miniaturized technology to assess cardiac function at multiple levels in the mouse, have added a wealth of new information to our understanding of the functional role of each of these membrane Ca²⁺-handling proteins in cardiac physiology and pathophysiology. Furthermore, these genetic models have provided valuable insights into the compensatory cross-talk mechanisms between the major membrane Ca²⁺-handling proteins in the mammalian heart.