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

ALLEVA K; CHARA OSVALDO; SUTKA M; AMODEO G

Montevideo

Congreso; 5th Southern Cone Biophysics Congress. 6th International Conference of Biological Physics.; 2007

IUPAP - SAB

Beta vulgaris storage root plasma membrane vesicles (PMV) are an excellent biological model to study water transport due to its highcapacity to move water (high water permeability involving aquaporins) which can be shut down by medium acidification. Spectroscopy oflight 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 betterunderstand 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 twonot necessarily equal water pathways through PMV, iii) there is no solute movement across the PMV. Simulations were performed usingEuler method with a custom made software developed in Visual Basic code. The procedure allows predicting time course of vesicle volumechanges following the hyperosmotic challenge. Preliminary results suggest that kinetics of vesicle volume changes can be explained as thecombined response of two different water pathways, one with high water osmotic permeability (HP) and other with low water osmoticpermeability (LP), being HP pathway the one that contributes with approximately 80% of the response. Interestingly, when the osmoticshock is performed at acidic pH, LP turns into the main pathway for the osmotic response. In this analysis it is clear that although thecontribution of HP to the overall response is almost lost, this water pathway is still present. The proposed mathematical model opens in thisway new perspectives that allow us to extend and clarify the phenomenological aspects involved in the interpretation of light scattering as auseful tool to analyze volume change and water movements in biological membranes.