Modulation of Phosphoinositide Monolayer Compressibilities by Physiological Levels of Ca2+

Abstract

Phosphoinositides (PIs) play a crucial role in many cellular processes that occur at the plasma membrane such as exocytosis and endocytosis. These processes not only locally enrich the membrane with PIs and are often accompanied by intracellular calcium release, but they also involve mechanical membrane deformations. Thus, the question arises how mechanical properties such as compressibility of highly negatively charged lipids such as phosphatidylinositol bisphosphate (PIP2) are modulated by physiological levels (0-1000nM) of Ca2+ ions. Using pure monolayers and a Langmuir film balance, we investigated the effect of bivalent ions on the compressibility of Phosphatidylinositol (PI), Phosphatidylinositol 4,5-bisphosphate (PIP2), 1,2-dioleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (DOPG)and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). In addition, we also present a theoretical framework that describes the relationship between electrical surface potentials and compressibilities which shows good agreement with our experimental findings.