This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.107.126615v1 95/3/1199    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Levental, I. Articles by Cebers, A. PubMed PubMed Citation Articles by Levental, I. Articles by Cebers, A.

Electrostatic Contribution to the Surface Pressure of Charged Monolayers Containing Polyphosphoinositides

I. Levental ^*, P. A. Janmey ^*  and A. Cbers 

^* Institute for Medicine and Engineering, Departments of Physics, Physiology, and Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania; and Institute of Physics, University of Latvia, Salaspils, Latvia

Correspondence: Address reprint requests to Paul A. Janmey, Tel.: 215-573-7380; E-mail: janmey{at}mail.med.upenn.edu.

Structural and functional studies of lateral heterogeneity in biological membranes have underlined the importance of membrane organization in biological function. Most inquiries have focused on steric determinants of membrane organization, such as headgroup size and acyl-chain saturation. This manuscript reports a combination of theory and experiment that shows significant electrostatic contributions to surface pressures in monolayers of phospholipids where the charge spacing is smaller than the Bjerrum length. For molecules with steric cross sections typical of phospholipids in the cell membrane (50 Ų), only polyphosphoinositides achieve this threshold. The most abundant such lipid is phosphatidylinositol bisphosphate, which has between three and four charged groups at physiological conditions. Theory and experiment show that surface pressure increases linearly with phosphatidylinositol bisphosphate net charge and reveal crossing of high and low ionic strength pressure-area isotherms, due to opposing effects of ionic strength in compressed and expanded monolayers. Theory and experiment show that electrostatic effects are negligible for monolayers of univalent lipids, emphasizing the unique importance of electrostatic effects for lateral organization of polyphosphoinositides. Quantitative differences between theory and experiment suggest that attractive interactions between polyphosphoinositides, possibly mediated by hydrogen bonding, can lessen the effect of electrostatic repulsions.