Effect of monovalent cations on polyvalent cation-induced fusion of phosphatidylserine small unilamellar vesicles

✍ Scribed by Dinesh K. Sukumaran; Shinpei Ohki

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 472 KB
• Volume: 49
• Category: Article
• ISSN: 0009-3084
• DOI: 10.1016/0009-3084(88)90059-x

✦ Synopsis

Fluorescence internal contents mixing assay was used to monitor the fusion of phosphatidylserine (PS) small unilamellar vesicles, initiated by metal ions (Ca 2", La 3" and Tb3*), at various concentrations of monovalent cations (Li', Na ÷ and K÷). The influence of ionic strength (0.02--1.0 M) on the threshold concentration of "fusogenic" cations required to induce fusion was measured. The threshold concentrations increased monotonically (1 mM at 0.1 M to 3.1 mM at 1 M) with the increasing ionic strength of the solution for Ca 2", but remained unchanged for both La ~" and Tb 3". Changes in the ionic strength of the encapsulated solution did not alter the threshold concentrations for all the ions studied, in the range 0.02--0.3 M. The results are analyzed in terms of competitive binding between the monovalent ions and the "fusogenic" ions (Ca 2", Tb 3÷ and La3÷). It is shown that there is a critical value for calcium bound-PS, below which no massive fusion occurs. Bound and free fractions of PS are calculated based on the Gouy-Chapman model, taking activities rather than concentrations of metal ions into account. Our experiments also show that monovalent ions alone do not induce fusion even at high concentrations.