Figure 4.

Cartoon of patch geometry under different conditions. Positive pressure generates high curvature where the membrane leaves the glass and begins pointing downward. Because dome tension is symmetric with respect to pressure, there seems to be no intrinsic way for channels in the dome to sense a particular sign of the pressure. Images of inside-out patches revealed that positive pressure peels the membrane off the wall (4, 26). The channels that are seen with positive pressure may represent channels activated in the region of extreme curvature, such as where the bound membrane is peeled off the glass and pushed toward the tip (33) (Figs. 3 and 4). It is also possible that the enormous stresses caused by positive-pressure extrusion rip loose the cytoskeleton to transfer local mean tension to the bilayer. To see this figure in color, go online.