inward outward 0 nase Na+ current Action Ca2+L-type current T-type potential transient ITO1 (4-AP-sensitive) and ion outward current To2 (Ca2+-activated) transport delayed rectifiers cI or lKp inward rectifier, Ik1 Fast response cell pacemaker current, If (…, see above Na*-Ca2+ exchange Na′,K+ ATPaseAction potential and ion transport Fast response cell