title: A computer model of lens structure and function predicts experimental changes to steady state properties and circulating currents.
abstract: BACKGROUND
  In a previous study (Vaghefi et al. 2012) we described a 3D computer model that used finite element modeling to capture the structure and function of the ocular lens. This model accurately predicted the steady state properties of the lens including the circulating ionic and fluid fluxes that are believed to underpin the lens internal microcirculation system. In the absence of a blood supply, this system brings nutrients to the core of the lens and removes waste products faster than would be achieved by passive diffusion alone. Here we test the predictive properties of our model by investigating whether it can accurately mimic the experimentally measured changes to lens steady-state properties induced by either depolarising the lens potential or reducing Na+ pump rate.
  
  
  METHODS
  To mimic experimental manipulations reported in the literature, the boundary conditions of the model were progressively altered and the model resolved for each new set of conditions. Depolarisation of lens potential was implemented by increasing the extracellular [K+], while inhibition of the Na+ pump was stimulated by utilising the inherent temperature sensitivity of the pump and changing the temperature at which the model was solved.
  
  
  RESULTS
  Our model correctly predicted that increasing extracellular [K+] depolarizes the lens potential, reducing and then reversing the magnitude of net current densities around the lens. While lowering the temperature reduced Na+ pump activity and caused a reduction in circulating current, it had a minimal effect on the lens potential, a result consistent with published experimental data.
  
  
  CONCLUSIONS
  We have shown that our model is capable of accurately simulating the effects of two known experimental manipulations on lens steady-state properties. Our results suggest that the model will be a valuable predictive tool to support ongoing studies of lens structure and function.
authors.affiliation: Department of Optometry and Vision Sciences, University of Auckland, Building 502, Level 4, 85 Park Road, Grafton, Auckland, New Zealand. e.vaghefi@auckland.ac.nz.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Vaghefi
authors.forename: Nancy
authors.initials: N
authors.lastname: Liu
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Donaldson
mesh_terms: D000818:Animals; D003198:Computer Simulation; D005110:Extracellular Space / Q000201:enzymology / Q000378:metabolism; D020342:Finite Element Analysis; D007908:Lens, Crystalline / Q000098:blood supply* / Q000166:cytology / Q000502:physiology*; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011920:Rats, Inbred WF; D012039:Regional Blood Flow; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium