Cell Cycle Dependent Modulation of Membrane Dipole Potential and Neurotransmitter Receptor Activity: Role of Membrane Cholesterol.

The cell cycle is a sequential multistep process essential for growth and proliferation of cells that make up multicellular organisms. A number of nuclear and cytoplasmic proteins are known to modulate the cell cycle. Yet, the role of lipids, membrane organization, and physical properties in cell cycle progression remains largely elusive. Membrane dipole potential is an important physicochemical property and originates due to the electrostatic potential difference within the membrane because of nonrandom arrangement of amphiphile dipoles and water molecules at the membrane interface. In this work, we explored the modulation of membrane dipole potential in various stages of the cell cycle in CHO-K1 cells. Our results show that membrane dipole potential is highest in the G1 phase relative to S and G2/M phases. This was accompanied by regulation of membrane cholesterol content in the cell cycle. The highest cholesterol content was found in the G1 phase with a considerable reduction in cholesterol in S and G2/M phases. Interestingly, we noted a similarity in the dependence of membrane dipole potential and cholesterol with progress of the cell cycle. In addition, we observed an increase in neutral lipid (which contains esterified cholesterol) content as cells progressed from the G1 to G2/M phase via the S phase of the cell cycle. Importantly, we further observed a cell cycle dependent reduction in ligand binding activity of serotonin1A receptors expressed in CHO-K1 cells. To the best of our knowledge, these results constitute the first report of cell cycle dependent modulation of membrane dipole potential and activity of a neurotransmitter receptor belonging to the G protein-coupled receptor family. We envision that understanding the basis of cell cycle events from a biophysical perspective would result in a deeper appreciation of the cell cycle and its regulation in relation to cellular function.