Copyright@ The McGraw-Hill Companies, Ine Permission required for reproduction or display. (depolarization of plasma membrane) Calcium ions regulate the Opening of plasma membrane L-type contraction of cardiac muscle: Ca<+ channels in T-tubules Flow of Ca2+ into cytosol the entry of extracellular calcium ions causes the Ca2+ binds to Ca2+ receptors (ryanodine receptors) release of calcium from the on the external surface of the sarcoplasmic reticulum sarcoplasmic reticulum (calcium-induced calcium Opening of Ca2+channels intrinsic to these receptors release钙诱导的钙释放],the source of about 95% of the Flow of Ca+into cytosol calcium in the cytosol. T Cytosolic Ca2+ concentration Contraction Excitation-contraction coupling in cardiac muscleCalcium ions regulate the contraction of cardiac muscle: the entry of extracellular calcium ions causes the release of calcium from the sarcoplasmic reticulum (calcium-induced calcium release [钙诱导的钙释放]), the source of about 95% of the calcium in the cytosol. Excitation-contraction coupling in cardiac muscle