title: Regulation by physiological cations of acetylcholine transport mediated by human OCTN1 (SLC22A4). Implications in the non-neuronal cholinergic system.
abstract: OBJECTIVE
  This study aimed to investigate the influence of physiological ions on the transport of acetylcholine which is catalyzed by the recombinant human Organic Cation Transporter Novel 1 (hOCTN1), thus being involved in the function of the non neuronal cholinergic system.
  
  
  METHODS
  The experimental model of proteoliposomes reconstituted with the hOCTN1 transporter obtained by over-expression in E. coli has been used. Uptake and efflux of [(3)H]acetylcholine in the proteoliposome system have been followed in the presence of different cations, mimicking the cell environment.
  
  
  RESULTS
  Internal K(+) stimulated, while external Na(+) strongly inhibited the uptake of [(3)H]acetylcholine in proteoliposomes. Strong inhibition was exerted also by external K(+) while Mg(2+) or sucrose had no effect. Differently, the efflux of [(3)H]acetylcholine from proteoliposomes was not influenced by external or internal Na(+) and was only marginally stimulated by internal K(+). By dose response analysis of the Na(+) inhibition, an IC(50) of 1.3 mM was derived. The kinetic analysis of the Na(+) effect revealed a competitive type of inhibition on acetylcholine uptake, i.e., Na(+) interacts with the same external binding site of acetylcholine with a Ki of 1.2 mM.
  
  
  CONCLUSIONS
  Acetylcholine transport catalyzed by hOCTN1 revealed an asymmetric regulation by Na(+). Since the orientation of the transporter in the liposomal membrane is the same as in native membranes, and on the basis of sidedness of inhibition, physiological acetylcholine is principally exported by the transporter. This implies a role in autocrine and paracrine effects in non neuronal tissues.
authors.affiliation: Department of Cell Biology, University of Calabria, Via P.Bucci 4c 87036 Arcavacata di Rende, Italy.
authors.forename: Lorena
authors.initials: L
authors.lastname: Pochini
authors.forename: Mariafrancesca
authors.initials: M
authors.lastname: Scalise
authors.forename: Michele
authors.initials: M
authors.lastname: Galluccio
authors.forename: Cesare
authors.initials: C
authors.lastname: Indiveri
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D001693:Biological Transport, Active; D002412:Cations / Q000378:metabolism*; D006801:Humans; D008081:Liposomes / Q000378:metabolism; D027701:Organic Cation Transport Proteins / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D027981:Symporters
chemical_list: D002412:Cations; D008081:Liposomes; D027701:Organic Cation Transport Proteins; C109807:SLC22A4 protein, human; D027981:Symporters; D012964:Sodium; D000109:Acetylcholine; D011188:Potassium