Identification of alpha 1-adrenoceptor subtypes in the rat vas deferens: binding and functional studies. |
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| Authors: | T. Ohmura M. Oshita S. Kigoshi I. Muramatsu |
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| Affiliation: | Department of Pharmacology, Fukui Medical School, Japan. |
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| Abstract: | 1. The alpha 1-adrenoceptor subtypes of the prostatic and epididymal portion of rat vas deferens were characterized in binding and functional experiments. 2. In saturation experiments, [3H]-prazosin bound to two distinct affinity sites in the epididymal portion of rat vas deferens (pKD = 10.1 +/- 0.13 and 9.01 +/- 0.15, Bmax = 507 and 1231 fmol mg-1 protein, respectively). In the prostatic portion [3H]-prazosin bound to a single affinity site (pKD = 9.82 +/- 0.04, Bmax = 924 fmol mg-1 protein). 3. In the displacement experiments, unlabelled prazosin displaced biphasically the binding of 200 pM [3H]-prazosin to the epididymal portion; the resulting two pKI values were consistent with the affinity constants obtained in the saturation experiments. WB4101 (2-(2,6-dimethoxy-phenoxyethyl)-amino-methyl-1,4-benzodioxane) and benoxathian also discriminated the two affinity sites in the epididymal portion and the population of low affinity sites for the three antagonists was approximately 40%. On the other hand, the prostatic portion predominantly showed a single affinity site for prazosin, WB4101 and benoxathian, although the presence of a small proportion (less than 10%) of the low affinity site could be detected. HV723 (alpha-ethyl-3,4,5-trimethoxy-alpha-(3-((2-(2-methoxyphenoxy)ethyl)-a min o)- propyl) benzeneacetonitrile fumarate) displaced the [3H]-prazosin binding monophasically with a low affinity in both halves. 4. Pretreatment with chlorethylclonidine (CEC) at concentrations higher than 1 microM inhibited 700 pM [3H]-prazosin binding to the prostatic portion by approximately 50%. However, the inhibition in the epididymal portion was much less (approximately 21% at 50 microM CEC).(ABSTRACT TRUNCATED AT 250 WORDS) |
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