Norepinephrine (NE) Can Bind to the β-Adrenergic Receptor and Speed

Essay

Norepinephrine (NE) can bind to the β-adrenergic receptor and speed up heart rate through the cAMP signaling cascade. The cAMP cascade results in the phosphorylation of a voltage-gated Ca²⁺ channel, which increases its open probability. For each situation below state if the Ca²⁺ channel open probability increases, decreases, or does not change.
A. Intracellular addition of cAMP, in the absence of application of NE
B. In the absence of NE application, the inability of GTP to dissociate from Gα
C. In the presence of NE application, the inability of GDP to dissociate from Gα