Immunocytochemical demonstration of glucose transporters in epiphyseal growth plate chondrocytes of young rats in correlation with autoradiographic distribution of 2-deoxyglucose in chondrocytes of mice

The epiphyseal growth plate, where chondrocytes proliferate and differentia te, is the major site for longitudinal bone growth, matrix synthesis and mi neralization. Glucose is an important energy source for the metabolism and growth of chondrocytes. The family of facilitative glucose transporters (GL UTs) mediates glucose transport across the plasma membrane in mammalian cel ls. We used immunocytochemical. methods with anti-GLUT antibodies to invest igate the localization of GLUTs in chondrocytes of the epiphyseal growth pl ate in 3 age groups of rats (3, 7, and 28 days after birth). Intense immuno reactivity of GLUT isoforms 1-5 was detected in chondrocytes of 3-day and 7 -day old rats, and all GLUTs were localized in the maturation zone of the h ypertrophic zone. On postnatal day 28, chondrocytes in the maturation zone showed intense GLUT1, 4 and 5 immunoreactivity, and weak GLUT2 and 3 immuno reactivity. In addition to chondrocytes in the maturation zone, those in th e degenerative zone and in the zone of provisional calcification showed str ong GLUT4 and 5 immunoreactivity. Autoradiography of bone sections from 4-w eek old mice injected with C-14-2-deoxyglucose showed high silver grain den sity within matrix tissue in the reserve and proliferative zones but not ar ound chondrocytes. However, in the hypertrophic zone, silver grain density was high in matrix and chondrocytes. These data indicate that chondrocytes in the hypertrophic zones use glucose as energy source. High levels of GLUT 4 expression imply that glucose use in chondrocytes is regulated by insulin . Expression of GLUT5 in chondrocytes suggests that fructose is also used a s an energy source.