  We study the deformation of a lipid membrane in response to a local pH
modification. Experimentally, a basic solution is microinjected close to a
giant unilamellar vesicle. A local deformation appears in the zone of the
membrane that is closest to the micropipette, and relaxes when the injection is
stopped. A theoretical description of this phenomenon is provided. It takes
fully into account the spatiotemporal evolution of the concentration of
hydroxide ions during and after the microinjection, as well as the linear
dynamics of the membrane. This description applies to a local injection of any
substance that reacts reversibly with the membrane lipids. We compare
experimental data obtained in the domain of small deformations to the results
of our linear description, and we obtain a good agreement between theory and
experiments. In addition, we present direct experimental observations of the pH
profile on the membrane during and after the microinjection, using pH-sensitive
fluorescent lipids.
