A 21-year-old man with insulin-dependent (type 1)diabetes mellitus who forgot to inject his insulin is seen in the emergency department.The following laboratory data are obtained: Serum [Na+] = 140 mEq/L (normal: 135 to 147 mEq/L) Serum [K+] = 6.5 mEq/L (normal: 3.5 to 5.0 mEq/L) Serum [HCO3-] = 10 mEq/L (normal: 22 to 28 mEq/L) Blood pH = 7.0 (normal: 7.35 to 7.45) Arterial partial pressure of carbon dioxide (Pco2)= 25 mm Hg (normal: 33 to 44 mm Hg) Serum glucose concentration = 1000 mg/dL (normal: 70 to 110 mg/dL) Which of the following plays the most important role in the generation of hyperkalemia in this man?