  Most biological molecules contain acido-basic groups that modulate their
structure and interactions. A consequence is that pH gradients, local
heterogeneities and dynamic variations are used by cells and organisms to drive
or regulate specific biological functions including energetic metabolism,
vesicular traffic, migration and spatial patterning of tissues in development.
While the direct or regulatory role of pH in protein function is well
documented, the role of hydrogen and hydroxyl ions in modulating the properties
of lipid assemblies such as bilayer membranes is only beginning to be
understood. Here, we review approaches using artificial lipid vesicles that
have been instrumental in providing an understanding of the influence of pH
gradients and local variations on membrane vectorial motional processes:
migration, membrane curvature effects promoting global or local deformations,
crowding generation by segregative polarization processes. In the case of pH
induced local deformations, an extensive theoretical framework is given and an
application to a specific biological issue, namely the structure and stability
of mitochondrial cristae, is described.
