Analysis of the source of heterogeneity in the osmotic response of plant membrane vesicles

ALLEVA K; CHARA OSVALDO; SUTKA M; AMODEO G

EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS

Springer

Lugar: Berlin / Heidelberg; Año: 2009 vol. 38 p. 175 - 184

0175-7571

Plasma membrane vesicles have been widelyemployed to understand the biophysics of water movements,especially when active aquaporins are present. Ingeneral, water permeability coefficients in these preparationsoutcome from the analysis of the osmotic response ofthe vesicles by means of light scattering. As from now, thisis possible by following a theoretical approach that assumesthat scattered light follows a single exponential function andthat this behavior is the consequence of vesicle volumechanges due to an osmotic challenge. However, someexperimental data do not necessarily fit to single exponentialsbut to double ones. It is argued that the observed doubleexponential behavior has two possible causes: differentvesicle population in terms of permeability or in terms ofsize distribution. As classical models cannot identify thissource of heterogeneity, a mathematical modeling approachwas developed based on phenomenological equations ofwater transport. In the three comparative models presentedhere, it was assumed that water moves according to anosmotic mechanism across the vesicles, and there is nosolute movement across them. Interestingly, when tested ina well described plasma membrane vesicle preparation, theapplication of these models indicates that the source ofheterogeneity in the osmotic response is vesicles havingdifferent permeability, clearly discarding the variable sizeeffect. In conclusion, the mathematical approach presentedhere allows to identify the source of heterogeneity; thisinformation being of particular interest, especially whenstudying gating mechanisms triggered in water channelactivity.