C. Mullins1, D. Zanella1, A. Galli1 1University Of Alabama at Birmingham, Division Of GI Surgery/Department Of Surgery, Birmingham, Alabama, USA
Introduction: Emerging evidence suggests a significant bidirectional relationship between the enteric system and motivated behaviors. This complex interaction is thought to be mediated, at least in part, by circulating systemic hormones originating in the gut. One such class of molecules are bile acids (BAs), which have previously been shown to regulate cocaine-associated behaviors. Prior research has suggested that BAs may interact directly with the dopamine (DA) transporter (DAT), a plasma membrane protein that fine-tunes DA neurotransmission by active reuptake of DA. Although, DAT has been identified as a target of BA mediation, the mechanisms underlying this interaction and its phenotypic implications remain unknown.
Methods: Cell-based electrophysiology techniques were used to mechanistically determine whether and how BAs interact with the DAT to alter its function in terms of DA release and reuptake. HEK 293 cells were stably transfected with either the human DAT (hDAT) or empty plasmid. Prior to recording, cells were bath-loaded with DA and washed in physiologic cell solution. Single cells for recording were identified via fluorescent markers and an amperometric electrode (carbon fiber) was placed in contact with the plasma membrane of the cell and held to a voltage matching the redox potential of DA. Either the BA obeticholic acid (OCA) or vehicle were perfused acutely the subsequent amperometric currents were recorded to completion. A positive deflection of the amperometric current signifies a flux of DA (DA efflux) from the cytoplasm of the cell to the extracellular environment.
Results: Acute perfusion of OCA induces a DA efflux with a kinetic that appears like the reverse of DAT function observed with of the perfusion of the psychostimulant amphetamine (AMPH). The observed effects were dependent on DAT expression, but independent of sodium and insensitive to chemical blockade of the DAT. Dose-response curves were also generated using different concentrations of OCA.
Conclusion: While further studies are required to better define BAs in the CNS, these findings can be foundational for targeted therapeutics for diseases of altered motivated behaviors, from psychostimulant abuse to hedonic feeding.
