COMPARISON OF THE SODIUM DEPENDENCY OF UPTAKE OF META-LODOBENZYLGUANIDINE AND NOREPINEPHRINE INTO CULTURED BOVINE ADRENOMEDULLARY CELLS

  • 1 January 1984
    • journal article
    • research article
    • Vol. 26  (3) , 539-546
Abstract
Radioiodinated m-iodobenzylguanidine (MIBG), a scintigraphic agent used for the detection of human pheochromocytomas, is thought to utilize the same uptake and retention mechanism(s) as norepinephrine (NE). Using cultured bovine adrenomedullary cells, the mechanism(s) of uptake of MIBG was compared to that of NE. Two different uptake systems were identified. NE and MIBG were taken up by a Na+-dependent system that was characterized by: temperature dependency; high affinity: Km of 1.22 .+-. 0.12 .mu.M for MIBG and 1.41 .+-. 0.50 .mu.M for NE; low capacity: Vm [metabolic rate] (pmol/106 cells/10 min) of 64.3 .+-. 3.3 for MIBG and 36.6 .+-. 7.2 for NE; saturability; ouabain sensitivity; and energy dependency. NE and MIBG also were taken up by a temperature-dependent, Na+-independent, apparently unsaturable and energy-independent system. The Na+-dependent uptake system fulfills many of the criteria for Uptake1 whereas the Na+-independent uptake system is most likely a passive diffusion process. NE uptake proceeded predominantly by the Na+-dependent process. Uptake of MIBG occurred by both pathways at low concentrations, but at high concentrations (> 10 .mu.M) uptake was predominantly (75-100%) by the Na+-independent process. Evidently, MIBG and NE are transported by the same carrier involved in the Na+-dependent system. Scintiscans of the human adrenals and pheochromocytomas appear to reflect uptake of [131I]MIBG by the Na+-dependent system.