description
Phase 1 of the cardiac action potential is the inactivation of the fast Na+ channels. The transient net outward current causing the small downward deflection (the "notch" of the action potetial) is due to the movement of K+ and Cl- ions. In pacemaker cells, this phase is due to rapid K+ efflux and closure of L-type Ca2+ channels (Park & Fishman 2011, Grant 2009)

external resources
NCBI:1339118
REACTOME:R-HSA-5576894
PUBMED:19808464
PUBMED:21357845

genes
KCND1 , KCND2 , KCND3 , KCNIP3 , KCNIP2 , KCNIP1 , KCNIP4 ,