Characterization of Inhibitor‐Sensitive and ‐Resistant Adenosine Transporters in Cultured Human Fetal Astrocytes

: The kinetic characteristics of [3H]adenosine uptake, the extent to which accumulated [3H]adenosine was metabolized, the effects such metabolism had on measurements of apparent Michaelis‐Menten kinetic values of KT and Vmax, and the sensitivities with which nucleoside transport inhibitors blocked [3H]adenosine accumulations were determined in cultured human fetal astrocytes. KT and Vmax values for accumulations of [3H]‐labeled purines using 15‐s incubations in the absence of the adenosine deaminase inhibitor erythro‐9‐(2‐hydroxy‐3‐nonyl)adenine (EHNA) and the adenosine kinase inhibitor 5′‐iodotubercidin (ITU) were 6.2 µM and 0.15 nmol/min/mg of protein for the high‐affinity and 2.6 mM and 21 nmol/min/mg of protein for the low‐affinity components respectively. In the presence of EHNA and ITU, where