pH dependence of corneal oxygen consumption.
OBJECTIVE
To determine whether corneal acidosis, which occurs during contact lens wear, alters corneal O2 consumption (QO2) and if so, whether increased ion transport activity could contribute to altered QO2 during acidosis.


METHODS
PO2 was measured, using the phosphorescence quenching of Pd-meso-tetra-(4-carboxyphenyl) porphine, in an airtight chamber that held a trephined rabbit cornea. The rate of change in chamber PO2 was used as a measure of QO2. QO2 was measured at pH 7.5 and then at either pH 6.7, 7.1, or 7.3. Measurements of QO2 at pHs 7.5 and 6.7 were repeated in the presence of 0.5 mM amiloride and 0.5 mM ouabain.


RESULTS
When pH was changed from 7.5 to 6.7, 7.1, or 7.3, O2 consumption increased by a factor of 1.80+/-0.11 (+/-SE), 1.65+/-0.12, and 1.44+/-0.06, respectively. Amiloride (0.5 mM) and ouabain (0.5 mM) inhibited 50% and 65%, respectively, of the increase in QO2 at pH 6.7.


CONCLUSIONS
Corneal acidosis leads to increased QO2 in a dose-dependent manner. The increased QO2 is in part secondary to the activation of pH regulatory mechanisms, including Na+/H+ exchange, which then stimulates Na+/ K+-ATPase activity. These findings indicate that contact lens-induced acidosis can exacerbate corneal hypoxia and related complications.
Harvitt
D M
DM
Vision Science Group and the Morton D. Sarver Center for Cornea and Contact Lens Research, University of California, School of Optometry, Berkeley, USA.
Bonanno
J A
JA
D000138:Acidosis / Q000378:metabolism*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D003315:Cornea / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006863:Hydrogen-Ion Concentration; D010042:Ouabain / Q000494:pharmacology; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D011166:Porphyrins / Q000378:metabolism; D011817:Rabbits; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism
D011166:Porphyrins; D017923:Sodium-Hydrogen Exchangers; D010042:Ouabain; C107018:porphine; D000584:Amiloride; D010100:Oxygen