Abstract
Purpose: :
To determine the extent of acidosis in normoglycemia and hyperglycemia by measuring pH profiles in the rat retina.
Methods: :
Double-barreled ion-selective microelectrodes were made to measure profiles throughout the retina of dark-adapted intact Long-Evans rats. Profiles were measured in the normal retina, and in acute hyperglycemia in vivo by penetrating to the choroid and then slowly withdrawing the electrode. The rats were anesthetized during preparation with a 2.5-3% isoflurane/35% O2 mixture and during recordings with urethane. The intraretinal electroretinogram (ERG) was evaluated to determine the retinal depth of the electrode.
Results: :
Under normoglycemic conditions, rats had an average [H+] of 4.21E-08 ± 3.78E-09 Moles/L (n=5 rats) at the choroid (pH= 7.37). The [H+] gradually increased as the electrode was withdrawn from the choroid through the retina, reaching a minimum pH of 7.10 in the outer nuclear later. The pH increased through the inner retina, to a vitreal value of pH=7.20. Acutely hyperglycemic rats (n=3, glucose 296.72 mg/dl) had an average choroidal, minimum outer retinal, and vitreous pH of 7.33, 7.05, and 7.12 respectively.
Conclusions: :
Intraretinal rat pH profiles are similar to those in cats during normoglycemia, and in acute hyperglycemia produced by a concentrated IV injection of glucose (Padnick-Silver and Linsenmeier, 2002). The extracellular pH in the retina, which is unusually acidic, acidifies still further under hyperglycemic conditions, particularly in the inner retina.
Keywords: pH regulation/protons • retina • metabolism