Effects of iodotubercidin on adenosine kinase activity and nucleoside transport in DDT1 MF-2 smooth muscle cells.
Iodotubercidin is an adenosine kinase inhibitor that through its ability to increase levels of endogenous adenosine can enhance adenosine's receptor-mediated effects. We investigated whether iodotubercidin can inhibit [3H]adenosine accumulation by inhibiting transport processes in addition to inhibition of intracellular trapping of labeled adenine nucleotides. Under conditions in which extensive metabolism of intracellular adenosine was present, [3H]adenosine accumulation by DDT1 MF-2 cells was almost completely inhibited by iodotubercidin and the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)-adenine or by the nucleoside transport inhibitor nitrobenzylthioinosine. By using similar conditions, [3H]adenosine accumulation was significantly greater in Na+ buffer than in buffer containing N-methyl-D-glucamine in place of Na+; however, this effect may be explained by an observed 40% inhibition of adenosine kinase activity by N-methyl-D-glucamine. By using uptake intervals of 14 sec to represent the transport component of uptake, iodotubercidin decreased the affinity for adenosine, by about 3-fold, but had no effect on maximum velocity of transport. That these effects of iodotubercidin were due to direct interactions with nucleoside transporters was supported by findings that iodotubercidin inhibited [3H]nitrobenzylthioinosine binding to nucleoside transporters with a Ki value of 4 microM and inhibited [3H]uridine and [3H]formycin B uptake with IC50 values of 7 and 15 microM, respectively. These data suggest that iodotubercidin, at pharmacologically relevant concentrations, inhibits nucleoside transport independently of its well characterized inhibition of adenosine kinase and that N-methyl-D-glucamine must be used with caution in experiments to determine the possible presence of Na+ gradient-dependent concentrative nucleoside transporters.
Parkinson
F E
FE
Department of Pharmacology, University of Manitoba, Winnipeg, Canada.
Geiger
J D
JD
D000248:Adenosine Kinase / Q000378:metabolism*; D000818:Animals; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D009130:Muscle, Smooth / Q000187:drug effects* / Q000201:enzymology; D009705:Nucleosides / Q000378:metabolism*; D011869:Radioligand Assay; D014372:Tubercidin / Q000031:analogs & derivatives* / Q000494:pharmacology
D009705:Nucleosides; C034214:5-iodotubercidin; D000248:Adenosine Kinase; D014372:Tubercidin