Effect of fluoride on phosphatidylserine-mediated calcium transport

Experiments to study the effect of F- on phosphatidylserine-mediated Ca2+ transport were performed utilizing two and three compartment lipid-aqueous phase model systems. Using the three compartment model, it was shown that F- modulated the rate of Ca2+ transport in a biphasic manner. Low concentrations of F- enhanced the Ca2+ translocation rate and high levels of F- inhibited the rate of Ca2+ transport. To determine whether the enhancement or inhibition of Ca2+ transport rate by F- was due to an increase in the uptake of Ca2+ into the lipid phase, or to an increase in the ability of the lipid phase to release Ca2+, a two compartment model was used. It was found that the ability of the phosphatidylserine phase to take up Ca2+ increased as the F- concentration of the aqueous donor phase was raised. In addition, Ca2+ release from the phosphatide was also modulated by F-. High F- levels inhibited the release of Ca2+ from the lipid, while low levels of F- did not retain Ca2+ in the lipid phase. Thus, it was concluded that F- enhanced the interaction between Ca2+ and phosphatidylserine, possibly by forming a phosphatidylserine-Ca-F complex. Once this interaction had taken place, Ca2+ release into the aqueous receiver compartment was dependent on the F- concentration. Thus, low F- levels induced a net increase in Ca2+ transport, while high F- levels inhibited Ca2+ translocation rates.