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Permeability of vesicular phospholipid bilayer membranes to thallium and its facilitation

1985; Elsevier BV; Volume: 817; Issue: 2 Linguagem: Inglês

10.1016/0005-2736(85)90021-5

1879-2642

I.R. Miller,

Thallium and Germanium Studies

The rate of release of TI+ from phospholipid vesicles of different composition was measured by pulse polarography as a function of temperature or in the presence of valinomycin, tetraphenylboron (TPB−) or dipicrylamine (DPA−) as transport facilitators. The release from pure dipalmitoylphosphatidylcholine (DPPC) vesicles increased abruptly around the pretransition temperature. The release from lipid mixtures with broad transition temperature region increased continuously with temperature. The steepness of the increase decreased with the width of the transition peak. Valinomycin, TPB− (tetraphenylboron) and DPA− (dipicrylamine) facilitate release of TI+ from unilamellar vesicles above their phase transition temperature with a first-order release rate constant. They do not facilitate release below the phase transition. Bursts of release were observed upon their addition to the vesicles but after annealing, which was completed within less than a minute, the vesicles were resealed. No facilitated release from multilamellar vesicles could be discerned. The entrapped volume into the multilamellar vesicles is determined from the difference between the maximal facilitated release and the total release after lysis of the liposomes by Triton X-100. The volume entrapped in the multilamellar vesicles determined this way amounted to 10–20% of the total entrapped volume.