Ionic Homeostasis Failure in Major Depressive Disorder: Ion Channel Mechanisms, Excitation-Inhibition Imbalance, and...

Major depressive disorder (MDD) remains a leading cause of disability; however, monoaminergic models do not fully explain delayed treatment onset, incomplete remission, or rapid responses to glutamatergic interventions. In this study, we proposed a system-level ionic homeostasis framework for MDD. In this model, genetic susceptibility, chronic stress, metabolic burden, and neuroinflammation converge in neuronal and glial ion-channel systems, disrupting calcium, potassium, chloride, and purinergic homeostasis. These disturbances alter intrinsic excitability, synaptic integration, inhibitory tone, glial buffering, and neuron-glia signaling, thereby promoting excitation-inhibition imbalance, impaired plasticity, and corticolimbic network instability. We reviewed the evidence implicating the CACNA1C/Cav1.2, TREK-1, KCNQ, NKCC1/KCC2, HCN, transient receptor potential/acid-sensing ion channels, and glial mediators, including P2X7R, Kir4.1, and AQP4. We also discuss how ketamine-related mechanisms, chloride-restoring strategies, anti-inflammatory ion channel targeting, neuromodulation, EEG biomarkers, and AI/multiomics approaches support mechanism-informed precision therapeutics. MDD could be conceptualized as a distributed failure of ionic homeostasis that links neuroinflammation, E/I imbalance, network instability, and impaired adaptive plasticity.