title: Cation transport mechanisms in Mycoplasma mycoides var. Capri cells. The nature of the link between K+ and Na+ transport.
abstract: We have studied the links between the mechanisms of Na(+), K(+) and H(+) movements in glycolysing Mycoplasma mycoides var. Capri cells. In the light of the results reported in the preceding paper [Benyoucef, Rigaud & Leblanc (1982) Biochem. J.208, 529-538], we investigated certain properties of the membrane-bound ATPase of Mycoplasma cells, with special reference to its ionic requirements and sensitivity to specific inhibitors. Our findings show, first, that, although Na(+) stimulated ATPase activity, K(+) did not affect it, and, secondly, that NN'-dicyclocarboidi-imide and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD) were potent inhibitors of the basal ATPase activity, which was unaffected by vanadate and ouabain. We also investigated the movements of Na(+) and H(+) under the experimental conditions applied to the study of the K(+) uptake reported in the preceding paper, and found that when ;Na(+)-loaded cells' previously equilibrated with (22)Na(+) were diluted in a sodium-free medium, addition of glucose induced a rapid efflux of (22)Na(+). This energy-dependent efflux was independent of the presence of KCl in the medium. Studies of the changes in internal pH by 9-aminoacridine fluorescence or [(14)C]methylamine distribution indicated that the movement of Na(+) was coupled to that of protons moving in the opposite direction, a finding that supports the presence of an Na(+)/H(+) antiport. When Na(+)-loaded cells are diluted in an Na(+)-rich medium the Na(+)/H(+) antiport is still active, but cannot decrease the intracellular Na(+) concentration. Under such conditions, net (22)Na(+) extrusion is specifically dependent on the presence of K(+) in the medium. The present results and those derived from the study of K(+) accumulation (the preceding paper) can be rationalized by assuming that Mycoplasma mycoides var. Capri cells contain two transport systems for Na(+) extrusion: an Na(+)/H(+) antiport and an ATP-consuming Na(+)/K(+)-exchange system.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002414:Cations, Monovalent / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects; D008954:Models, Biological; D009176:Mycoplasma mycoides / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D002414:Cations, Monovalent; D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium