Vesicle deformations

M616ard, Philippe, Electromechanical Properties of Model Membranes and Giant Vesicle Deformations, 6, 185 see also Bivas, Isak, 6, 207. 

While vesicle deformation in AC fields concerns stationary shapes, DC pulses induce short-lived shape deformations. In different studies, the pulse duration has been typically varied from several microseconds to milliseconds, while studies on cells have investigated a much wider range of pulse durations-from tens of nanoseconds to milliseconds and even seconds [80], as discussed in other chapters of this book. Various pulse profiles, unipolar or bipolar, as well as trains of pulses have been also employed (e.g., [81, 82]). Because the application of both AC flelds and DC pulses creates a transmembrane potential, vesicle deformations of similar nature are to be expected in both cases. However, the working fleld strength for DC pulses is usually higher by several orders of magnitude. Thus, the degree of deformation can be different. 

In the presence of salt in a vesicle exterior, unusual shape changes are observed during an applied DC pulse [107]. The vesicles adopt spherocylindrical shapes (Figure 7.5) with lifetimes of the order of 1ms. These deformations occur only in the presence of salt outside the vesicles, irrespective of their inner content (note that, in the absence of salt in the external solution, the vesicles deform only into prolates see Figure 7.5a). When the solution conductivities inside and outside are identical, Ain vesicles with square cross section are observed (Figure 7.5d). For the case Ain < the vesicles adopt disc-like shapes (Figure 7.5c), while in the... 

Vlahovska, P.M., Gracia, R.S., Aranda-Espinoza, S., and Dimova, R. (2009) Electrohydrodynamic model of vesicle deformation in alternating electric fields. Biophysical Journal, 96 (12), 4789-4803. 

Marmottant P, Hilgenfeldt S (2003) Controlled vesicle deformation and lysis by single oscillating bubbles. Nature 423 153... 

Electromechanical Properties of Model Membranes and Giant Vesicle Deformations... 

The following section presents some experimental results obtained in the study of giant vesicles using optical microscopy, beginning with bending elasticity measurements of different model membrane systems. Observations made on giant vesicle deformations induced by low-frequency electric fields are also discussed. 

This paper shows how the mechanical properties of model membranes can be measured by the study of giant vesicle deformations. This presentation is by no means exhaustive. Other studies demonstrate how closed objects, such as giant vesicles, can change their shape as a fiinction of a precise tuning of their geometric characteristics and their molecular distribution [60-63]. 

Other groups have also reported that the shape change of the vesicles occurred as a result of actin polymerization, but without showing the shape of vesicles during the deformation, except for one study [12]. As pointed out above, lipid membrane is easily deformed, and one should continuously observe individual vesicles to ensure that the vesicle deformation is coupled to the actin poljnnerization. 

Fig. 27 Temporal evolution of vesicle deformation and inclination angle 0, for V = 0.78...

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