Which of the following is true for SA node cardiac muscle cells?
A. An increase in the binding of norepinephrine to beta-adrenergic receptors in SA node cells will lead to an increase in intracellular levels of cAMP in these cells.
B. A decrease in intracellular levels of cAMP in SA node cells will lead to a decrease in the amount of time between two successive action potentials in SA node cells.
C. An increase in the binding of acetylcholine to muscarinic ACh receptors in SA node cells will lead to an increase in heart rate.