Effect of monovalent cations on polyvalent cation-induced fusion of phosphatidylserine small unilamellar vesicles.
Fluorescence internal contents mixing assay was used to monitor the fusion of phosphatidylserine (PS) small unilamellar vesicles, initiated by metal ions (Ca2+, La3+ 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 Ca2+, but remained unchanged for both La3+ and Tb3+. 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 (Ca2+, Tb3+ 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.
Sukumaran
D K
DK
Department of Biophysical Sciences, School of Medicine, State University of New York, Buffalo 14214.
Ohki
S
S
D000818:Animals; D001667:Binding, Competitive; D002412:Cations / Q000494:pharmacology*; D002414:Cations, Monovalent / Q000494:pharmacology*; D002417:Cattle; D008094:Lithium / Q000494:pharmacology; D008561:Membrane Fusion / Q000187:drug effects*; D010718:Phosphatidylserines / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology
D002412:Cations; D002414:Cations, Monovalent; D010718:Phosphatidylserines; D008094:Lithium; D012964:Sodium; D011188:Potassium