HTR3A Receptor Signaling in Human Disease: From Bioelectrical Regulation to Therapeutic Targeting

The 5-hydroxytryptamine receptor 3A (HTR3A) is the principal subunit of the 5-HT3 receptor and the only ionotropic member of the serotonin receptor family, mediating rapid cation influx and membrane depolarization following stimulation by serotonin. Beyond its established role in neurotransmission, growing evidence indicates that HTR3A functions as a critical regulator of bioelectrical signaling, influencing calcium homeostasis, neuronal excitability, immune responses, and diverse cellular processes implicated in human disease. This narrative review provides a comprehensive overview of the molecular structure, physiological functions, and pathological significance of HTR3A, with particular emphasis on its role in integrating bioelectrical mechanisms across multiple organ systems. Current evidence linking HTR3A dysregulation to cancer, neurological and psychiatric disorders, gastrointestinal diseases, inflammatory conditions, and pain is critically evaluated, highlighting shared electrophysiological pathways that may underlie these seemingly distinct pathologies. We further discuss the therapeutic potential of HTR3A-targeted interventions, including the repurposing of clinically approved 5-HT3 receptor antagonists, and examine emerging opportunities for biomarker development and precision medicine. Although substantial progress has been made in elucidating the biological functions of HTR3A, significant challenges remain regarding its context-dependent roles, mechanistic complexity, and clinical translation. By integrating molecular, electrophysiological, and translational evidence, this review proposes a unifying framework in which HTR3A-mediated bioelectrical signaling represents a common mechanistic axis linking diverse human diseases, thereby providing new perspectives for future mechanistic investigations and targeted therapeutic strategies.