  We study a dynamical curvature instability caused by a local chemical
modification of a phospholipid membrane. In our experiments, a basic solution
is microinjected close to a giant unilamellar vesicle, which induces a local
chemical modification of some lipids in the external monolayer of the membrane.
This modification causes a local deformation of the vesicle, which then
relaxes. We present a theoretical description of this instability, taking into
account both the change of the equilibrium lipid density and the change of the
spontaneous membrane curvature induced by the chemical modification. We show
that these two types of changes of the membrane properties yield different
dynamics. In contrast, it is impossible to distinguish them when studying the
equilibrium shape of a vesicle subjected to a global modification. In our
model, the longest relaxation timescale is related to the intermonolayer
friction, which plays an important part when there is a change in the
equilibrium density in one monolayer. We compare our experimental results to
the predictions of our model by fitting the measured time evolution of the
deformation height to the solution of our dynamical equations. We obtain good
agreement between theory and experiments. Our fits enable us to estimate the
intermonolayer friction coefficient, yielding values that are consistent with
previous measurements.
