Review Question - QID 109637

An 85-year-old male presents to the emergency room complaining of chest pain. He reports an intense pressure over his sternum and difficulty breathing. His past medical history is notable for two prior myocardial infarctions, hyperlipidemia, and hypertension. He takes aspirin, metoprolol, atorvastatin, lisinopril, and hydrochlorothiazide. The patient drinks socially and does not smoke. His temperature is 99°F (37.2°C), blood pressure is 150/85 mmHg, pulse is 130/min, and respirations are 24/min. An electrocardiogram demonstrates ST elevations in leads II, III, and aVF. Despite appropriate care, the patient expires. An autopsy is performed that demonstrates an area of ischemia in the cardiac region supplied by the right coronary artery. A small sample of cells from healthy tissue near the site of injury is isolated and is subjected to additional testing. A current is run across the cells resulting in an action potential as seen in Figure A. The ion channel responsible for maintaining the plateau in Figure A is also responsible for which of the following?