Muscle

In all three types of muscle cells - skeletal, cardiac, and smooth – Ca(2+) plays a major role in excitation-contraction (EC) coupling, i.e., the sequence of events that links electrical stimulation to contraction (or, in nonexcitable smooth muscle, the events that link agonist stimulation to contraction). In skeletal and cardiac muscle, an action potential arriving from a neuron is propagated along the membrane of the muscle cell, and penetrates deep into the interior of the cell via invaginations of the cell membrane, called T-tubules. This action potential causes the release of Ca(2+) from the sarcoplasmic reticulum, which then allows the crossbridge cycle to develop force (Huxley, 1957; Bers, 2001).