In Cardiac Muscle

In cardiac muscle

A) calcium ions do not bind to troponin molecules.
B) calcium ions play no role in the process of contraction.
C) calcium ions play an important role in repolarizing the membrane after the depolarization phase.
D) at least half of the calcium ion required for contraction comes from outside the cell.
E) calcium ions are not released from the sarcoplasmic reticulum.