Mathematical modelling of water transport across Beta vulgaris storage root plasma membrane vesicles under hyperosmotic challenges

KARINA ALLEVA; OSVALDO CHARA; MOIRA SUTKA; GABRIELA AMODEO

Montevideo, Uruguay

Congreso; 6th International Conference on Biological Physics and 5th Southern Cone Biophysics Congress; 2007

Sociedades Latinoamericana de Biofisica, del Cono Sur, Argentina

Beta vulgaris storage root plasma membrane vesicles (PMV) are an excellent biological model to study water transport due to its high capacity to move water (high water permeability involving aquaporins) which can be shut down by medium acidification.  Spectroscopy of light scattering under stopped flow conditions has been used to study the osmotic response of these vesicles to hyperosmotic shock. However, in these studies it has been considered that PMV behave as a single population in terms of osmotic water movement. To better understand water transport pathways, a mathematical approach was developed to analyze experimental data without assuming this limitation. The proposed model considers the following hypothesis: i) water moves according to an osmotic mechanism across PMV, ii) there are two not necessarily equal water pathways through PMV, iii) there is no solute movement across the PMV. Simulations were performed using Euler method with a custom made software developed in Visual Basic code. The procedure allows predicting time course of vesicle volume changes following the hyperosmotic challenge. Preliminary results suggest that kinetics of vesicle volume changes can be explained as the combined response of two different water pathways, one with high water osmotic permeability (HP) and other with low water osmotic permeability (LP), being HP pathway the one that contributes with approximately 80% of the response. Interestingly, when the osmotic shock is performed at acidic pH, LP turns into the main pathway for the osmotic response. In this analysis it is clear that although the contribution of HP to the overall response is almost lost, this water pathway is still present. The proposed mathematical model opens in this way new perspectives that allow us to extend and clarify the phenomenological aspects involved in the interpretation of light scattering as a useful tool to analyze volume change and water movements in biological membranes.