Two distinct alpha 1-adrenoceptor subtypes in rabbit liver: a binding study

British Journal of Pharmacology
T Ohmura, I Muramatsu

Abstract

1. The characteristics of alpha 1-adrenoceptor subtypes present on rabbit liver membranes were determined by radioligand binding and compared with the characteristics of binding in rat liver. 2. In saturation experiments using rabbit liver, [3H]-prazosin bound to two distinct affinity sites (pKD = 10.3 +/- 0.19 and 8.13 +/- 0.17, Bmax = 11.6 +/- 3.3 and 657.8 +/- 198.0 fmol mg-1 protein, respectively). In studies using rat liver, [3H]-prazosin bound to a single affinity site (pKD = 9.98 +/- 0.27, Bmax = 190.5 +/- 38.5 fmol mg-1 protein). 3. In competition experiments, unlabelled prazosin displaced biphasically the binding of 200 pM [3H]-prazosin to the rabbit liver; the resulting two pK1 values (9.85 +/- 0.08 and 8.01 +/- 0.09) were consistent with the affinity constants obtained in the saturation experiments. Two sites were also recognized by doxazosin (pKI 9.73 +/- 0.78 and 8.12 +/- 0.34), 2-(2,6-dimethoxy phenoxyethyl)-aminomethyl-1,4-benzo-dioxane (WB4101) pKI (9.74 +/- 0.32 and 7.57 +/- 0.34) and 5-methylurapidil (pKI 8.69 +/- 0.27 and 6.75 +/- 0.35), and the population of low affinity sites for the three antagonists was approximately 70%. Two distinct affinity constants (pKI 8.55 +/- 0.09 and 7.90 +/- 0.09) were also calc...Continue Reading

References

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