Improved culture conditions stimulate gluconeogenesis in primary cultures of renal proximal tubule cells

Unlike renal proximal tubule cells (RPTC) in vivo, RPTC cultured in standard conditions are hypoxic, glycolytic, and not gluconeogenic. This study investigated the effects of glucose and lactate on glycolysis and gluconeogenesis in rabbit RPTC cultured in conditions of increased oxygen supply (Shake). Confluent Shake cultures grown in the presence of glucose exhibited increased oxygen consumption and decreased glycolysis compared with stationary (Still) cultures. Addition of 5 mM lactate to a 5 mM glucose medium decreased net glucose consumption and glucose oxidation in Shake cultures by 34 and 50%, respectively, and resulted in net lactate consumption. Addition of 5 mM lactate to a glucose-free medium resulted in a threefold increase in net glucose production (0.024 ± 0.003 vs. 0.074 ± 0.013 μmol · mg protein^-1 · day^-1) in Shake cultures. Net glucose production further increased to 0.430 ± 0.020 and 1.640 ± 0.040 μmol · mg protein^-1 · day^-1 when glucose reuptake was inhibited by 1 mM phloridzin or 1 mM phloridzin + 1 mM phloretin, respectively. These results show that, under conditions of improved oxygenation and in the presence of lactate and physiological levels of glucose and insulin, RPTC aerobic metabolism increases and glucose metabolism changes from glycolysis and net lactate production to gluconeogenesis and net lactate consumption.