Figure 4.

Volume effects on metabolite release rates depend on O₂ availability and mass action. While apical media volumes differ, basal media volumes are constant across all conditions, so release of metabolites into the basolateral media will be unaffected by mass action. (A) The release rate of m+3 lactate derived from ¹³C₆-glucose into the apical (black dots) or basal (pink dots) chambers from 4 to 22 hours in hfRPE is similarly affected by apical media volume, confirming O₂ availability is the dominant factor affecting release. Similar analysis for (B) m+3 pyruvate, also derived from glycolysis, where only basally secreted pyruvate is affected. (C, D) Particularly on the basal side, which is unaffected by mass action, mitochondrial intermediates from glucose are also affected by media volume: (C) m+2 citrate and (D) m+2 malate (n = 5–6, donors 3, 4, and 5).