ELECTROSTATIC POTENTIALS AND BIOLOGICAL MEMBRANES

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The long-term objective is to describe the electrostatic and electrokinetic properties of biological membranes. There are six specific aims: (i) to investigate the discreteness-of-charge effect using positive as well as negative membranes, polyvalent as well as monovalent lipids, and frozen as well as fluid bilayers; (ii) to measure the interaction of polyvalent lipids (e.g., phosphatidylinositol 4, 5-bisphosphate, PIP2) with proteins that have several positive charges close to the membrane-solution interface (e.g., glycophorin, melittin, rhodopsin); (iii) to determine the electrostatic potential 1 nm from the surface of a charged membrane; (iv) to investigate the electrostatic and electrokinetic properties of model and biological membranes that have charges a significant distance from the membrane- solution interface; (v) to study the ion exchange properties of PIP2; (vi) to evaluate the role electrostatic potentials play in exocytosis. Established experimental techniques will be used to measure: the conductance of planar bilayers, the surface potential of monolayers, the 31P NMR spectra of sonicated vesicles, the fluorescence (from the probe TNS) of vesicles, and the electrophoretic mobility of both lipid vesicles and biological membranes. A new fluorescence technique will be developed; fluorescent probes will be attached to defined locations on gangliosides, the fluorescence quenched with the cations tempamine or thallium, and the potential estimated from the Boltzmann relation. The results from all these techniques will be compared with the predictions of classical theories (either the Gouy-Stokes equations) and with the predictions of a modern statistical mechanical theory developed by S. Marcelja, who will collaborate on this project. The experimental results, and theoretical concepts that will emerge from these results, are health related because PIP2 is the source of two second messengers in the cell and gangliosides are involved in cell-cell recognition. For example, an antibody with a high affinity for the ganglioside GD3 has recently been shown to be effective in the treatment of melanomas. Information about the biophysical properties of PIP2 and gangliosides should thus be of interest to many physiologists, biochemists, cell biologists and clinicians.