Glycogenolysis versus glucose transport in human granulocytes: Differential activation in phagocytosis and chemotaxis

Granulocytes depend primarily on anaerobic glycolysis to supply the necessary energy for locomotion and chemotaxis. Either transmembrane transport of extracellular glucose or catabolism of intracellular glucose can supply glycolytic substrate. In this report, using enzymatic analysis of granulocyte glycogen, we describe conditional requirements for glycogenolysis, namely phagocytosis. With abundant extracellular glucose, granulocyte glycogen content (12.2 ± 1.6 μg/10⁶ cells) is not depleted whether or not incubations include various soluble chemotaxins (e.g., FMLP, C5a(des arg), arachidonic acid). These chemotaxins accelerate transmembrane glucose uptake. With near complete absence (<6 mg/dl) of extracellular glucose, both resting and chemotaxin (FMLP, C5a(des arg), arachidonic acid) stimulated granulocytes catabolize significant endogenous glycogen. Phagocytosis, however, fails to enhance glucose uptake and promotes glycogen consumption even with abundant extracellular glucose. Simple particle-phagocyte attachment without internalization (produced by cytochalasin-B) also promoted glycogen consumption, suggesting that this membrane deformation alone is a sufficient trigger for glycogenolysis. Resting or chemotactic granulocytes, therefore, can adapt their energy source pending extracellular glucose availability - often compromised at inflammatory sites - while phagocytic cells depend primarily, if not exclusively, on endogenous glycogen stores. This differential metabolic activation defends the granulocytes energy supply and may be critical in supporting antimicrobial activity in acute inflammation.