title: [3H]dipyridamole binding to guinea pig brain membranes: possible heterogeneity of central adenosine uptake sites.
abstract: The binding of [3H]dipyridamole ([3H]DPR) to guinea pig brain membranes is described and compared to that of [3H]nitrobenzylthioinosine ([3H]NBI). The binding of [3H]DPR is saturable, reversible, and specific with pharmacologic evidence indicating that this ligand is binding to the adenosine uptake site. Compared to [3H]NBI the binding of [3H]DPR is of higher capacity (Bmax = 208 +/- 16 fmol/mg protein for [3H]NBI and 530 +/- 40 fmol/mg protein for [3H]DPR) and lower affinity (KD = 0.35 +/- 0.02 nM for [3H]NBI and 7.6 +/- 0.7 nM for [3H]DPR). The adenosine uptake inhibitors are the most potent inhibitors of binding (Ki of 10(-8)-10(-7) M) whereas adenosine receptor ligands such as cyclohexyladenosine, 2-chloroadenosine, and various methylxanthines are several orders of magnitude less potent (Ki 10(-5)-10(-2). The inhibition of [3H]DPR binding by NBI is biphasic, with only 40% of binding being susceptible to inhibition of NBI concentrations less than 10(-5) M. The tissue distribution of [3H]DPR binding parallels that of [3H]NBI although in most cases significantly more sites are observed with [3H]DPR. Calcium channel blocking agents such as nifedipine, nimodipine, and verapamil are also inhibitors of [3H]DPR binding with potencies in the micromolar range. The data are consistent with [3H]DPR being a useful additional ligand for the adenosine uptake site and provide evidence that multiple uptake binding sites exist of which only about 40% are NBI-sensitive.
mesh_terms: D000241:Adenosine / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D004176:Dipyridamole / Q000378:metabolism*; D006168:Guinea Pigs; D007700:Kinetics; D008297:Male; D013868:Thioinosine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D002121:Calcium Channel Blockers; D013868:Thioinosine; D004176:Dipyridamole; C001789:4-nitrobenzylthioinosine; D000241:Adenosine