Which of the following statements concerning the differences between action potentials in skeletal muscle cells and in ventricular cardiac muscle cells is TRUE?
A. After sodium influx through voltage-gated channels occurs in ventricular cells, prolonged influx of calcium from the extracellular fluid occurs. No such calcium influx occurs in skeletal muscle cells.
B. The efflux of K+ repolarizes skeletal muscle cells after an action potential, while repolarization in cardiac muscle cells is due to the efflux of Ca2+.
C. Unlike skeletal muscle cells, the initial depolarization of ventricular cells is mainly due to calcium influx, not sodium influx.
D. Action potentials in skeletal muscle cells are longer in duration than action potentials in cardiac muscle cells.
E. Like skeletal muscle cells, ventricular cardiac muscle cells have a resting membrane potential closer to the sodium equilibrium potential than to the potassium equilibrium potential.
Answer: A
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