title: Mathematical model of TMA+ diffusion and prediction of light-dependent subretinal hydration in chick retina.
abstract: OBJECTIVE
  To derive a mathematical model of TMA+ diffusion across the retina that can be used to estimate the amplitude and kinetics of the light-evoked increase in subretinal hydration and its effect on the concentration of other ions.
  
  
  METHODS
  All experimental data were obtained in chick retina-pigment epithelium-choroid preparations as described in the accompanying paper.
  
  
  RESULTS
  Diffusional properties of the retina were derived from the time course of [TMA+]o in the subretinal space (SRS) after changes in the retinal perfusate. Then, the SRS volume changes underlying the light-induced [TMA+]o response can be derived using a mathematical model of TMA+ diffusion. Complete retinal depth series of light-evoked [TMA+]o responses could be simulated by producing a corresponding expansion of the SRS. Volume changes inferred from the diffusion model were 2.2 to 3.8 times larger and more prolonged than could be derived directly from delta [TMA+]o. The model predicted up to a 20% peak increase in subretinal-space hydration during illumination. The effects of this volume increase on subretinal K+ and Ca2+ were estimated. These predictions were supported by inhibiting the volume increase with DIDS, which blocks retinal pigment epithelium basal membrane Cl- conductance.
  
  
  CONCLUSIONS
  The primary source of light-evoked changes in extracellular TMA+ concentration recorded throughout the retina is an increase in hydration (volume) of the subretinal space. The response spreads to the inner retina by diffusion. Effects of TMA+ diffusion lead to large underestimates of the underlying volume changes. The light-evoked volume change alters the composition of the subretinal space and light-induced responses of other ions.
authors.affiliation: Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg.
authors.forename: V I
authors.initials: VI
authors.lastname: Govardovskii
authors.forename: J D
authors.initials: JD
authors.lastname: Li
authors.forename: A V
authors.initials: AV
authors.lastname: Dmitriev
authors.forename: R H
authors.initials: RH
authors.lastname: Steinberg
mesh_terms: D000818:Animals; D001834:Body Water / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002645:Chickens; D002829:Choroid / Q000378:metabolism; D004058:Diffusion; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism; D005731:Ganglionic Stimulants / Q000378:metabolism*; D008954:Models, Biological; D010775:Photic Stimulation; D010786:Photoreceptor Cells / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012160:Retina / Q000378:metabolism* / Q000502:physiology
chemical_list: D005731:Ganglionic Stimulants; D000644:Quaternary Ammonium Compounds; C027917:tetramethylammonium; D011188:Potassium; D002118:Calcium