The incorporation of solubilized choline-transport activity into liposomes.
The choline-transport system has been solubilized from synaptic plasma membrane by using either sodium cholate or Triton X-100, and re-incorporated into unilamellar liposomes by using the technique of cholate dialysis. The criteria of choline-transport activity were saturability by excess choline, inhibition by hemicholinium-3, and trans-activation (i.e. stimulation of the uptake of [3H]choline into liposomes by preloading them with non-radioactive choline). Liposomes prepared from detergent extracts of synaptic plasma membrane and added lipid showed uptake of [3H]choline fulfilling these three criteria. Data on choline-transport activity of liposomes at various choline concentrations could be interpreted as implying that the transport system has two apparent Km values (2-5 microM and 50-100 microM), or alternatively that the system is composed of two or more negatively co-operating subunits (or units). It was shown by t.l.c. that the transported radioactivity was choline and that it was not significantly acetylated. Replacing Na+ by K+ on the outside of these liposomes partially inhibited uptake, and the formation of a potential gradient (inside negative) with valinomycin increased the total but not the saturable components of uptake when liposomes were prepared in a K+ medium, and transferred to an Na+ medium.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002793:Cholic Acids; D002794:Choline / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D003956:Dialysis; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008081:Liposomes / Q000378:metabolism*; D008954:Models, Biological; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D012995:Solubility; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism
D002793:Cholic Acids; D003902:Detergents; D008081:Liposomes; D000255:Adenosine Triphosphate; D012964:Sodium; D002794:Choline; D011188:Potassium