Comparison of [3H]tamsulosin and [3H]prazosin binding to wild-type and constitutively active alpha1B-adrenoceptors.
We have tested the hypothesis that smaller alpha1B-adrenoceptor labeling by [3H]tamsulosin compared to [3H]prazosin is related to differential recognition of agonist low affinity states. Paired saturation binding experiments with [3H]prazosin and [3H]tamsulosin were performed in membrane preparations from rat liver and Rat- fibroblasts stably transfected with wild-type hamster alpha1B-adrenoceptors or a constitutively active mutant thereof. In all three settings [3H]tamsulosin labeled significantly fewer alpha1B-adrenoceptors than [3H]prazosin. In noradrenaline competition binding experiments, the percentage of agonist low affinity sites was smallest for the constitutively active alpha1B-adrenoceptor but the percentage of agonist low affinity sites recognized by [3H]tamsulosin and [3H]prazosin did not differ significantly. We conclude that [3H]tamsulosin labels fewer alpha1B-adrenoceptors than [3H]prazosin but this is not fully explained by a poorer labeling of agonist low affinity sites.
Hein
P
P
Dept of Medicine, University of Essen, Klinikum Essen, Germany.
Goepel
M
M
Cotecchia
S
S
Michel
M C
MC
D000317:Adrenergic alpha-Antagonists / Q000378:metabolism*; D000818:Animals; D006224:Cricetinae; D008297:Male; D011224:Prazosin / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D013449:Sulfonamides / Q000378:metabolism*; D000077409:Tamsulosin; D014316:Tritium
C547718:Adra1b protein, rat; D000317:Adrenergic alpha-Antagonists; D018340:Receptors, Adrenergic, alpha-1; D013449:Sulfonamides; D014316:Tritium; D000077409:Tamsulosin; D011224:Prazosin