A 24-year-old man is admitted to the hospital for the treatment of bacterial endocarditis secondary to intravenous drug use. He is started on broad-spectrum intravenous antibiotics in the emergency room and is being transferred to his room upstairs. Enroute, he develops severe hypotension and is unresponsive. In an attempt to treat his shock, you decide to use norepinephrine. Which of the following statements is true concerning the effects of norepinephrine on cardiac pacemaker cells?
