Cation transport mechanisms in Mycoplasma mycoides var. Capri cells. Na+-dependent K+ accumulation.
We have studied some features of K+ accumulation by glycolysing Mycoplasma mycoides var. Capri cells. We report that when Na+ is absent from the external medium, K+ accumulates up to the level predicted by the amplitude of the transmembrane electrical potential, delta psi m, measured by Rb+ and methyltriphenylphosphonium cation (TPMP+) distribution. Therefore, under these experimental conditions, the coupling mechanism of K+ uptake consists of a delta psi m-driven uniport. More important, when Na+ is present in the external medium, the level of K+ accumulation by glycolysing Mycoplasma cells is far too steep to be equilibrium with delta psi m (-120 mV for delta muK+ compared with -90mV for delta muRb+ or delta muTPMP+). Our results clearly indicate the presence in Mycoplasma of an active K+-transport system specifically stimulated by Na+. Furthermore, by controlling the amplitude of the energy-dependent delta muH+, we obtain strong evidence that this specific Na+-stimulated K+ transport is modulated by the transmembrane electrical potential. Finally, we show that ATP is consumed when such a transport system is in activity.
D000255:Adenosine Triphosphate / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002414:Cations, Monovalent / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009176:Mycoplasma mycoides / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010756:Phosphoric Acids / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology*
D002414:Cations, Monovalent; D010756:Phosphoric Acids; D000255:Adenosine Triphosphate; D012964:Sodium; C030242:phosphoric acid; D011188:Potassium