Tributyltin-mediated exchange diffusion of halides in lipid bilayers

Area of Science:

• Biochemistry
• Membrane Biophysics
• Toxicology

Background:

• Lipid bilayers are crucial barriers in biological systems.
• Understanding ion transport across membranes is vital for cellular function.
• Tributyltin (TBT) is a known environmental pollutant with potential biological effects.

Purpose of the Study:

• To investigate the effect of tributyltin (TBT) on inorganic anion permeability in phosphatidyl ethanolamine (PE) lipid bilayers.
• To elucidate the mechanism by which TBT influences anion transport.
• To quantify the relationship between TBT concentration, chloride flux, and membrane properties.

Main Methods:

• Formation of PE lipid membranes in NaCl or KCl solutions.
• Measurement of electrical conductance and 36Cl self-exchange flux.
• Varied anion concentrations and TBT concentrations to determine flux dependencies.
• Measurement of interfacial potentials to assess TBT's effect on membrane dipole potential.

Main Results:

• TBT increased chloride self-exchange flux by orders of magnitude (10^-12 to 10^-8 mol.cm^-2.s^-1) without changing membrane conductance.
• Chloride flux followed the relationship MCl = B[TBT][Cl].
• Anion permeability sequence was I > Br > Cl > F > NO3.
• TBT chloride reduced the intrinsic dipole potential of PE membranes by ~70 mV.

Conclusions:

• TBT enhances inorganic anion permeability in lipid bilayers through an obligatory exchange diffusion mechanism.
• The interaction between TBT and anions occurs at the membrane surface, influencing membrane potential.
• These findings provide insights into TBT's mechanism of action at the molecular level.