Received for publication November 5, 2007.
Revised March 5, 2008.
Accepted for publication March 6, 2008.

Protease-Activated Receptor-1 Mediates Thrombin-Induced Persistent Sodium Current in Human Cardiomyocytes

Abstract

Following the thrombus formation in cardiac cavities or coronaries, the serine protease thrombin is produced and can therefore reach the myocardial tissue by the active process of extravasation and binds to the G protein-coupled protease-activated receptor-1 (PAR1) expressed in human myocardium. The role of PAR1 was investigated in the thrombin effect on sodium current (I_Na). I_Na was recorded in freshly isolated human atrial myocytes by the whole-cell patch-clamp method. Action potentials (AP) were recorded in guinea pig ventricular tissue by the conventional glass microelectrodes technique. Thrombin-activated PAR1 induced a tetrodotoxin-blocked persistent sodium current, I_NaP, in a concentration-dependent manner with an apparent EC₅₀ of 28 U/ml. The PAR1 agonist peptide SFLLR-NH₂ (50 µM) was able to mimic PAR1-thrombin action, whereas PAR1 antagonists, SCH 203099 (10 µM) and ER 112787 (1 µM), completely inhibited it. The activated-PAR1 involves calcium-independent phospholipase-A2 signaling pathway since two inhibitors of this cascade, bromoenol lactone (50 µM) and haloenol lactone suicide substrate (50 µM), block PAR1-thrombin-induced I_NaP. As a consequence of I_NaP activation, in guinea pig right ventricle papillary muscle, action potential duration (APD) were significantly increased by 20% and 15% under the respective action of 32 U/ml thrombin and 50 µM SFLLR-NH₂, and these increases in APD were prevented by 1 µM TTX or markedly reduced by application of 1 µM SCH 203099 or ER 112787. Thrombin, through PAR1 activation, increases persistent component of the Na current resulting in an uncontrolled sodium influx into the cardiomyocyte which can contribute to cellular injuries observed during cardiac ischemia.

Key words: Thrombin/PAR, Sodium, Gs family, Phospholipase A2's, Ischemia/Reperfusion