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Alexandra Boussommier Calleja, W Daniel Stamer, C Ethier, Darryl Overby; Metabolic Dependence of Conventional Outflow Facility in Mice. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3537.
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© ARVO (1962-2015); The Authors (2016-present)
Conventional aqueous humor outflow is considered to be a process independent of cellular metabolism. In particular, previous studies have shown outflow facility to be relatively unaffected by metabolic poisons or changes in temperature (after accounting for temperature effects on perfusion media viscosity). Our goal was to determine whether conventional outflow facility in mice is similarly independent of cellular metabolism.
Enucleated eyes from C57BL/6 mice were perfused within 3 hrs of death at sequential pressures (4, 8, 15, 25 mmHg) while submerged in isotonic saline under temperature control. Conventional outflow facility was calculated as the slope of the best-fit linear regression of flow rate vs. pressure. One group of paired eyes was perfused with PBS + 5.5 mM glucose, with one eye at 20°C and the fellow eye at 35°C. A second group was perfused similarly, but with PBS + a metabolic poison (2 mM sodium azide) + 10 mM dideoxy-D-glucose.
Eyes perfused at 35°C without poison had a 2.49±0.86 fold higher conventional facility vs. eyes perfused at 20°C (0.0069±0.0021 vs. 0.0171±0.0028 µl/min/mmHg; N = 6 vs. 6; p = 4 x 10-5; Mean±SD). Importantly, this temperature-dependent increase was significantly larger than the predicted 1.39-fold increase based on viscosity change alone (p=4 x 10-3). In contrast, eyes perfused with metabolic poison showed a 1.52±0.81 fold increase in facility with increasing temperature (0.0087±0.0035 vs. 0.0132±0.0046; N = 7 vs. 5; p=0.107), which was not significantly different from the expected viscosity change (p=0.346).
In these preliminary experiments, a metabolic poison eliminated the temperature-dependent increase in conventional outflow facility in mouse eyes. In contrast to past data from perfused human cadaver eyes (VanBuskirk, AJO 1974 77:565), our data in mice suggest that conventional outflow depends partially on cellular metabolism. These differences could reflect underlying species differences, differences in perfusion methodology or post mortem time.
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