Which of the following statements about membrane potentials in different types of cardiac cells is TRUE?

A)Myocardial cells have a resting membrane potential of about -90 mV;pacemaker cells do not have a true resting membrane potential.
B)Once threshold depolarization is reached in both myocardial and pacemaker cells,the rapid upswing of the action potential is caused by the opening of voltage-gated Na⁺ channels
C)Voltage-gated transient (T-type) Ca²⁺ channels are present in all of the different types of cells of the heart.
D)There are no L-type Ca²⁺ channels in cardiac muscle cells.
E)The upstroke of the action potential is steeper in SA node cells than it is in Purkinje cells.