  Directly examining subcellular mechanics whilst avoiding excessive strain of
a live cell requires the precise control of light stress on very small areas,
which is fundamentally difficult. Here we use a glass nanopipet out of contact
with the plasma membrane to both exert the stress on the cell and also
accurately monitor cellular compression. This allows the mapping of cell
stiffness at a lateral resolution finer than 100 nm. We calculate the stress a
nanopipet exerts on a cell as the sum of the intrinsic pressure between the tip
face and the plasma membrane plus its direct pressure on any glycocalyx, both
evaluated from the gap size in terms of the ion current decrease. A survey of
cell types confirms that an intracellular pressure of approximately 120 Pa
begins to detach the plasma membrane from the cytoskeleton and reveals that the
first 660 +/- 90 nm of compression of a neuron cell body is much softer than
previous methods have been able to detect.
