A 38-year-old man presents to the emergency department with severe palpitations, tremor, and anxiety. His blood pressure is 165/95 mmHg and heart rate is 128 bpm. Serum glucose is 285 mg/dL. A diagnosis of pheochromocytoma is suspected. During the acute catecholamine surge, which of the following intracellular signaling cascades is MOST directly responsible for the increase in cardiac contractility and lipolysis observed in this patient?