Fig. 2.

Shape transformations of a lipid membrane tubule. (A) The tubule conductance as a function of L. D₁/D₂ ≈ 50, D₂ ≈ 2 μm, μ = 1 cP. The left G-axis corresponds to I and III and the right G-axis corresponds to II. (B) Fluorescent microscopy of the tubule; D₁/D₂ ≈ 3.2, D₂ ≈ 60 μm, μ = 15.4 cP. (Upper) An example of the tubule shape transition. The first image corresponds to the catenoidal tubule at L ≈ L_c, and the next frames were taken at +30, +60, and +90 ms. To visualize the membranes on the end-rings after the tubule shape transformation, a small positive pressure between the tubule exterior and interior was applied; this pressure did not significantly alter the catenoidal shape. (Lower) The satellite vesicles (arrowheads in Upper) move with the increase of the length between the end-rings. (Bars, 20 μm.) (C) The calculated contours of WT (black curves), NT (blue curves), and unstable catenoid (red curves; see Appendix); 1 designates the right end-ring, and 2a, 2b, and 2c designate the left end-ring at different L (1.1l_c, 0.6L_c, and 0.9L_c, respectively). The 3D shapes are constructed by rotation of the contours around the x-axis as shown by the arrow. End-rings with similar diameters were chosen for clarity (D₁/D₂ = 1/3, d = 0.1D₁). (D) The drop of the tubule conductance (G)at constant L ≈ L_c, tubule parameters as in A; the break in time axis is for ≈76 s. The arrow indicates the tubule rupture by a mechanical disturbance.