The control of calcium influx by cytoplasmic calcium in mammalian heart muscle

The role of Ca²⁺ in the initiation and maintenance of contraction has been extensively studies. Many of these studies have focused on how Ca²⁺ influx and efflux affect cytoplasmic Ca²⁺ (Ca_i) and, therefore, contraction in cardiac muscle. However, it has recently become apparent that Ca_i itself may play a major role in the control of Ca²⁺ influx and efflux from cardiac muscle. Here we review current ideas on the mechanisms underlying Ca²⁺ homeostasis in cardiac muscle, with specific attention to how Ca_i may control Ca²⁺ influx, both under normal and pathological conditions.