Enhanced glutamine and glucose metabolism in cultured rat splenocytes stimulated by phorbol myristate acetate plus ionomycin.
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Metabolism of glutamine and glucose was studied in normal rat splenocytes cultured for 48 hours in the presence and absence of a mixture of the mitogens, phorbol myristate acetate (PMA) + ionomycin (Iono). 3H-Thymidine uptake by splenocytes was stimulated more than 500-fold by PMA + Iono. After culture, cells were incubated for 2 hours in the presence of either 2 mmol/L [U-14C]glutamine +/- 5 mmol/L glucose or 5 mmol/L [U-14C]glucose +/- 2 mmol/L glutamine in Krebs-Ringer HEPES buffer. Glutamine was metabolized mainly to ammonia, glutamate, aspartate, and CO2, and these products were all increased (P less than .01) by twofold to 2.5-fold in stimulated cells. Glucose was metabolized mainly to lactate and, to a lesser extent, to pyruvate and CO2. Lactate production from glucose was increased (P less than .01) by 2.4-fold in stimulated cells, without changes in pyruvate or CO2 production. In unstimulated, cultured splenocytes, glutamine was not quantitatively as important as glucose in the provision of adenosine triphosphate (ATP), as calculated on the basis of measured metabolites. However, in stimulated cells, glutamine became a much more important energy substrate, providing similar amounts of ATP to those from glucose. The oxidation of glutamine via the Krebs cycle was the major pathway for glutamine-derived ATP production, while lactate production from glucose accounted for the major part of glucose-derived ATP in PMA+Iono-stimulated splenocytes. Thus, we suggest glutamine plays a dual metabolic role in these cells, as both an important fuel and an essential source of carbon and nitrogen precursors for biosynthetic processes.(ABSTRACT TRUNCATED AT 250 WORDS)
