Figure 1. Possible effects of serotonin or catecholamines on cardiac myocytes.

Serotonin (5-HT), released from the activated platelets, and catecholamines (NE, DA) released from the intracardiac nerves, interact with their receptors present at the level of the sarcolemma to exert their effects. Once this interaction is over, the majority of the neurotransmitter is rapidly re-uptaken through the transporter present in the membrane of the nerve terminal (NET, DAT) and only small percent escapes into the circulation or is uptaken through the extraneuronal monoamine transporter (EMT), present in the cardiomyocyte membrane. Once in the cytoplasm, these neurotransmitters are degraded by monoamine oxidases (MAO) and generate H₂O₂ that, in turn, might affect cellular processes even in the physiological conditions.