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Effects of ionophores on the phospholipid flippase activity of gastric vesicles

H Suzuki1, M Morii, N Takeguchi

  • 1Department of Pharmaceutical Physiology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama, 930-0194, Japan.

The Japanese Journal of Physiology
|December 22, 1999
PubMed

Insights

Gastric phospholipid flippase activity is modulated by ionophores and cations. Valinomycin/K+ inhibits flippase, while protonophores like CCCP/FCCP accelerate it, suggesting membrane state influences transport efficiency.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Membrane Transport

Background:

  • A magnesium-dependent ATP-dependent phospholipid flippase has been identified in gastric cells.
  • Understanding the regulation of this flippase is crucial for gastric physiology.

Purpose of the Study:

  • To investigate the effects of ionophores and monovalent cations on gastric Mg(2+)-ATP-dependent phospholipid flippase activity.
  • To elucidate the mechanisms by which these agents modulate phospholipid translocation.

Main Methods:

  • Utilized fluorescent analogues of phosphatidylcholine to monitor translocation.
  • Examined the impact of ionophores (valinomycin, CCCP, FCCP) and potassium ions (K+) on flippase activity.
  • Assessed the Mg(2+)-dependent ATPase activity of the flippase.
  • Employed the gastric flippase inhibitor SCH 28080.

Main Results:

  • Valinomycin inhibited phosphatidylcholine translocation in the presence of K+, with inhibition dependent on both agent concentrations.
  • Protonophores CCCP and FCCP significantly accelerated translocation (190-270%), an effect abolished by SCH 28080.
  • CCCP/FCCP did not affect the Mg(2+)-dependent ATPase activity, indicating a variable phospholipid/ATP coupling ratio potentially influenced by membrane fluidity.
  • Valinomycin-K+ inhibition was reversed by CCCP or FCCP.

Conclusions:

  • Gastric phospholipid flippase activity is sensitive to specific ionophores and monovalent cations.
  • Protonophores may alter membrane properties affecting translocation efficiency, independent of direct ATPase inhibition.
  • The interaction between ionophores, cations, and the flippase highlights complex regulatory mechanisms in phospholipid transport.

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