Quantification of in vivo anaerobic metabolism in the normal cat retina through intraretinal pH measurements

Abstract

We examined intraretinal [H+] in the intact retina of anesthetized cats using H+-sensitive microelectrodes to obtain spatial profiles of extracellular [H+]. One H+ is produced when an anaerobically generated ATP is utilized. We theorized that H+ production directly reflects anaerobic glucose consumption. From the choroid (pH ∼7.40), [H+]o steadily increased to a maximum concentration in the proximal portion of the outer nuclear layer (pH∼7.20). The shape of the profile was always concave down, indicating that a net production of H+ occurred across the avascular outer retina. A three-layer diffusion model of the outer retina was developed and fitted to the data to quantify photoreceptor H+ extrusion into the extracellular space (QOR-H+). It was determined that the outer segment (OS) layer had negligible H+ extrusion. The data were then refitted to a special three-layer model in which the OS layer QH+ was set equal to zero, but in which the inner segments and outer nuclear layer produced H+. The resulting QOR-H+ was several orders of magnitude lower than previous measurements of QOR-lactate, which were based on choroidal mass balances of lactate.