. 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.
A
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