SLC22A3 and Hypertension: Therefore, OCT-3 may be important in the homeostatic regulation of extracellular 5-HT levels by ensuring (albeit low-affinity) uptake of 5-HT, particularly in the face of constitutively reduced expression or function of the SERT such as that seen in hypertension or during treatment with selective serotonin re-uptake inhibitors (Hirano et al., 2005; Mirza et al., 2007).