Modeling and testing functional interactions among corneal endothelial acid-base transporters

In a healthy cornea, optimal corneal hydration and transparency is maintained by the corneal endothelial cells that pump fluid out of the stroma. The pump requires the action of three stromal- facing transport proteins: the Na+/CO3= cotransporter NBCe1 and the H+/Lactate- transporter MCT1. However, it is unclear why mutations in another protein, the pH-dependent H+ conductor SLC4A11, cause loss of pump function and thence corneal dystrophy. We hypothesize that SLC4A11 supports the activity of the pump by counteracting pH changes that result from imbalances in NBCe1 and MCT1 action. Understanding the complex functional interactions among these three acid-base transporters with co-expression studies only is virtually impossible because intuition alone is not sufficient for data interpretation. Mathematical models, developed in conjunction with experimental approaches, provide a powerful tool to overcome this difficulty. Thus, here we propose to use experimental data gathered from Xenopus oocytes expressing these transporters singly, in pairs, or as a trio, in combination with kinetic parameters that have been determined for each transporter, to generate a computational model that mimics our in vitro experiments. This multidisciplinary approach will allow us quantify the power of SLC4A11 to prevent pH change during imbalanced NBCe1/MCT1 action, disclose synergistic and antagonistic interactions among the three, and predict the effects of disease-causing mutations that shift the abundance and/or pH dependence of SLC4A11 on intracellular pH balance and on the ion fluxes that support pump function.