Thrombin facilitation of voltage-gated sodium channel activation in human cardiomyocytes: implications for ischemic sodium loading.
BACKGROUND
Thrombin plays a role in mediating ischemic injury and cardiac arrhythmias, but the mechanisms involved are poorly understood. Because voltage-gated sodium channels (VGSCs) have not previously been considered, putative effects of thrombin on VGSC function were investigated in human isolated cardiomyocytes.


RESULTS
Sodium current (I(Na)) was recorded by the whole-cell patch-clamp method. Thrombin increased peak I(Na) amplitude in an activity-dependent manner, from 1 to 100 U/mL, with an apparent EC50 of 91+/-16 U/mL. When tested at 32 U/mL, thrombin-increased I(Na) was abolished by tetrodotoxin (50 micromol/L). Thrombin effects on I(Na) were reversible and repeatable, and 100 U/mL doubled peak I(Na) amplitude. Thrombin (32 U/mL) shifted I(Na) activation to hyperpolarized potentials without affecting steady-state inactivation, producing unusually large increases in window current. Hirudin (320 U/mL) or haloenol lactone suicide substrate (10 micromol/L) failed to significantly affect these effects of thrombin. In current-clamped cardiomyocytes, thrombin (32 U/mL) depolarized resting membrane potential by 10 mV.


CONCLUSIONS
Facilitation of VGSC activation causing large increases in window current is a major mechanism by which thrombin may promote ischemic sodium loading and injury.
Pinet
Caroline
C
Centre Nationale de la Recherche Scientifique, Unité Mixte de Recherche 8078, Hôpital Marie Lannelongue, Le Plessis Robinson, France.
Le Grand
Bruno
B
John
Gareth W
GW
Coulombe
Alain
A
D000200:Action Potentials; D000368:Aged; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006629:Hirudins / Q000494:pharmacology; D006801:Humans; D015640:Ion Channel Gating; D017136:Ion Transport; D008564:Membrane Potentials / Q000187:drug effects; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000209:etiology; D009206:Myocardium / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011753:Pyrones / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000502:physiology*; D013917:Thrombin / Q000494:pharmacology*
D006629:Hirudins; D009281:Naphthalenes; D011753:Pyrones; D015222:Sodium Channels; C068314:6-(bromomethylene)tetrahydro-3-(1-naphthaleneyl)-2H-pyran-2-one; D012964:Sodium; D013917:Thrombin