Vitamin K modulates cardiac action potential by blocking sodium and potassium ion channels.
BACKGROUND
Cardiovascular collapses, syncopes, and sudden deaths have been observed following the rapid administration of intravenous vitamin K. Our objectives were to characterize the effects of vitamin K on cardiac action potentials and to evaluate effects of vitamin K on sodium and potassium currents, namely I(Na), I(Kr), and I(Ks).


RESULTS
Guinea pig hearts (n = 21) were paced at a cycle length of 250 msec and exposed to vitamin K at 1.15-4.6 micromol/L (2.5-10 mg/L). Monophasic action potential duration measured at 90% repolarization (MAPD(90)) was not significantly reduced (-1.6 +/- 0.3 msec; P >.05; N.S.) at 1.15 micromol/L, but increased by 6.5 +/- 0.4 msec (P <.05) at 2.3 micromol/L. MAPD(90) was not measurable at 4.6 micromol/L, as a result of inexcitability. Patch-clamp experiments in ventricular myocytes demonstrated a approximately 50% reduction in I(Na) by 10 micromol/L vitamin K and a concentration-dependent reduction of the K(+) current elicited by short depolarizations (250 msec; I(K250)). Estimated IC(50) for I(K250), mostly representing I(Kr), was 2.3 micromol/L. Vitamin K was less potent to block the K(+) current elicited by long depolarizations (5,000 msec; I(K5000)), mostly representing I(Ks), with an estimated IC(50) over 100 micromol/L.


CONCLUSIONS
Therapeutic concentrations ( approximately 1.5 micromol/L) of intravenous vitamin K modulate cardiac action potential by blocking ionic currents involved in cardiac depolarization and repolarization.
Drolet
B
B
Institut de cardiologie de Québec, Hôpital Laval et Université Laval, Sainte-Foy, Québec, Canada.
Emond
A
A
Fortin
V
V
Daleau
P
P
Rousseau
G
G
Cardinal
R
R
Turgeon
J
J
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D016757:Death, Sudden, Cardiac / Q000209:etiology; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000502:physiology; D007262:Infusions, Intravenous; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D015222:Sodium Channels / Q000187:drug effects* / Q000502:physiology; D013575:Syncope / Q000139:chemically induced / Q000503:physiopathology; D014812:Vitamin K / Q000008:administration & dosage / Q000494:pharmacology*
D015221:Potassium Channels; D015222:Sodium Channels; D014812:Vitamin K