Determinants of Deoxyglucose Uptake in Cultured Astrocytes: The Role of the Sodium Pump

Glucose utilization in primary cell cultures of mouse cerebral astrocytes was studied by measuring uptake of tracer concentrations of 3H]2-deoxyglucose (3H]2-DG). The resting rate of glucose utilization, estimated at an extracellular K+ concentration (K+]o) of 5.4 mM, was high (7.5 nmol glucose/mg protein/min) and was similar in morphologically undifferentiated and "differentiated" (dibutyryl cyclic AMP-pretreated) cultures. Resting uptake of 3H]2-DG was depressed by ouabain, by reducing K+]o, and by cooling. These observations suggest that resting glucose utilization in astrocytes was dependent on sodium pump activity. Sodium pump-dependent uptake in 2-3-week-old cultures was about 50% of total 3H]2-DG uptake but this fraction declined with culture age from 1 to 5 weeks. Uptake was not affected by changes in extracellular bicarbonate concentration (HCO3-]o) in the range of 5-50 mM but was significantly reduced in bicarbonate-free solution. At high HCO3-]o (50 mM) uptake was insensitive to pH (pH 6-8), whereas at low HCO3-]o (less than 5 mM) uptake was markedly pH-dependent. Elevation of K+]o from 2.3 mM to 14.2-20 mM (corresponding to extremes of the physiological range of K+]o) resulted in a 35-43% increase in 3H]2-DG uptake that was not affected by culture age or by morphological differentiation. Our results indicate a high apparent rate of glucose utilization in astrocytes. This rate is dynamically responsive to changes in extracellular K+ concentration in the physiological range and is partially dependent on sodium pump activity.