Pacemaker potentials and action potential of pacemaker cells of the heart 1. Pacemaker potential; This slow depolarization is due to both opening of Na+ channels and closing of K+ channels.
2. Depolarization; Action potential begins when pacemaker potential reaches threshold (-40mV). Depolarization is due to Ca2+ influx through Ca2+ channels
3. Repolarization; Is due to Ca2+ channels closing and K+ channels opening. This allows K+ efflux (flowing out), which brings the membrane potential back to its most negative value