The structure and dynamics of patch-clamped membranes: a study using differential interference contrast light microscopy

We have developed techniques for micromanipulation under high power video microscopy. We have used these to study the structure and motion of patch-clamped membranes when driven by pressure steps. Patch-clamped membranes do not consist of just a membrane, but rather a plug of membrane-covered cytoplasm. There are organelles and vesicles within the cytoplasm in the pipette tip of both cell-attached and excised patches. The cytoplasm is capable of active contraction normal to the plane of the membrane. With suction applied before seal formation, vesicles may be swept from the cell surface by shear stress generated from the flow of saline over the cell surface. In this case, patch recordings are made from membrane that was not originally present under the tip. The vesicles may break, or fuse and break, to form the gigasealed patch. Patch membranes adhere strongly to the wall of the pipette so that at zero transmural pressure the membranes tend to be normal to the wall. With transmural pressure gradients, the membranes generally become spherical; the radius of curvature decreasing with increasing pressure. Some patches have nonuniform curvature demonstrating that forces normal to the membrane may be significant. Membranes often do not respond quickly to changes in pipette pressure, probably because viscoelastic cytoplasm reduces the rate of flow through the tip of the pipette. Inside-out patches may be peeled from the walls of the pipette, and even everted (with positive pressure), without losing the seal. This suggests that the gigaseal is a distributed property of the membrane-glass interface.