Serotonin uptake via plasma membrane monoamine transporter during myocardial ischemia‐reperfusion in the rat heart in vivo

Serotonin (5‐HT) accumulates in the heart during myocardial ischemia and induces deleterious effects on the cardiomyocytes through receptor‐dependent and monoamine oxidase‐dependent pathways. We aimed to clarify the involvement of extra‐neuronal monoamine transporters in the clearance of 5‐HT during ischemia and reperfusion in the heart. Using a microdialysis technique in the anesthetized Wistar rat heart, we monitored myocardial interstitial 5‐HT and 5‐hydroxyindole acetic acid (5‐HIAA) concentration by means of electro‐chemical detection coupled with high‐performance liquid chromatography (HPLC‐ECD). Effects of inhibitors of the plasma membrane monoamine transporter (PMAT) and the organic cation transporter 3 (OCT3) (decynium‐22 and corticosterone) on the 5‐HT and 5‐HIAA concentrations during baseline, coronary occlusion, and reperfusion were investigated. Basal dialysate 5‐HT concentration were increased by local administration of decynium‐22, but not by corticosterone. Addition of fluoxetine, a serotonin transporter (SERT) inhibitor further increased the 5‐HT concentration upon during administration of decynium‐22. Decynium‐22 elevated the background level of 5‐HT during coronary occlusion and maintained 5‐HT concentration at a high level during reperfusion. Production of 5‐HIAA in the early reperfusion was significantly suppressed by decynium‐22. These results indicate that PMAT and SERT independently regulate basal level of interstitial 5‐HT, and PMAT plays a more important role in the clearance of 5‐HT during reperfusion. These data suggest the involvement of PMAT in the monoamine oxidase‐dependent deleterious pathway in the heart.