The mechanosensitive channel of large conductance (MscL), shown superimposed on a snapshot from an all-atom simulation of a POPC bilayer, is subject to both positive and negative lateral pressures within the membrane. On the right, regions of positive net pressure, colored red, tend to compress the channel, while regions of negative pressure, colored blue, tend to expand it. Water (blue), lipid acyl chains (cyan), phosphate groups (yellow), and ester oxygens (green) all interact to produce the complex pressure profiles revealed in the paper; the total mass density is shown in black.