Inositol metabolism during neuroblastoma B50 cell differentiation: effects of differentiating agents on inositol uptake.
Inositol uptake was studied in the rat CNS neuroblastoma B50 cell line. Eadie-Hofstee analysis of the uptake pattern reveals two defined modes of inositol entry into the cell. The high-affinity uptake component requires the presence of extracellular sodium and is inhibited by phloridzin. Analysis of the uptake velocities of the high-affinity uptake component provided the following apparent kinetic parameters: Km = 13.7 microM and Vmax = 14.7 pmol/mg of protein/min (without correcting for residual diffusion) and Km = 12.9 microM and Vmax = 12.3 pmol/mg of protein/min (with correction). At physiological concentrations, the high-affinity transport process contributes approximately 70% to total uptake; the remainder is due to a low-affinity diffusion-like process. Uptake inhibition studies reveal that the uptake process is sensitive to ouabain, amiloride, and dichlorobenzamil inhibition but relatively insensitive to cytochalasin B or phloretin. When neuroblastoma B50 cells are induced to differentiate morphologically with high extracellular calcium or with dibutyryl cyclic AMP, a significant decrease in inositol uptake is observed. The dibutyryl cyclic AMP-mediated inhibition of uptake affects only the high-affinity uptake component and is noncompetitive in nature. The high extracellular calcium-mediated inhibition is less specific; it involves "disappearance" of the high-affinity process, some inhibition of the low-affinity process, and an increase of inositol efflux. The significance of these observations is discussed in the context of neuroblastoma B50 cell differentiation.
Reboulleau
C P
CP
Department of Biological Sciences, Rutgers University, Newark, NJ 07102.
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D003571:Cytochalasin B / Q000494:pharmacology; D007294:Inositol / Q000378:metabolism*; D007700:Kinetics; D009447:Neuroblastoma / Q000378:metabolism* / Q000473:pathology; D010042:Ouabain / Q000494:pharmacology; D010693:Phloretin / Q000494:pharmacology; D010695:Phlorhizin / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D014407:Tumor Cells, Cultured
C041470:3',4'-dichlorobenzamil; D003571:Cytochalasin B; D007294:Inositol; D010042:Ouabain; D003994:Bucladesine; D000584:Amiloride; D012964:Sodium; D010695:Phlorhizin; D010693:Phloretin; D002118:Calcium