Subclassification of presynaptic α-adrenoceptors: α-autoreceptors in rabbit atria and kidney.
In: Naunyn-Schmiedeberg's Archives of Pharmacology, Jg. 352 (1995-07-01), Heft 1, S. 31-42
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Zugriff:
The study was devised to classify, by means of antagonist affinities, the presynaptic α-autoreceptors of rabbit atria and kidney in terms of α, α, α and α-A set of antagonists was chosen that was able to discriminate between the four subtypes. Small pieces of the left atrium and slices of the kidney cortex were preincubated with H-Noadrenaline and then superfused and stimulated electrically. In one series of experiments, tissue pieces were stimulated by relatively long pulse trains (1 or 2 min) leading to α-autoinhibition. All 11 (atria) or 10 (kidney) antagonists increased the evoked overflow of tritium. pEC values (concentrations causing 30% increase) were interpolated from concentration-response curves. In a second series of experiments, tissue pieces were stimulated by brief pulse trains (0.4 s) that did not lead to α-autoinhibition, and concentration-inhibition curves of the α-selective agonist 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14,304) were determined. Most of the 11 (atria) or 8 (kidney) antagonists shifted the concentration-inhibition curve of UK 14,304 to the right. pK values of the antagonists were calculated from the shifts. pEC values correlated with pK values, both in atria ( r = 0.728) and in the kidney ( r = 0.930). pEC values in atria correlated with pEC values in the kidney ( r = 0.988) and pK values in atria correlated with pK values in kidney ( r = 0.923). It is concluded that the α-autoreceptors in atria and the kidney are the same. Comparison with antagonist affinities for prototypic native α binding sites, α binding sites in cells transfected with α subtype genes, and previously classified presynaptic α-adrenoceptors - all taken from the literature - indicates that both autoreceptors are α. This conclusion is reached with either of the two independent estimates of autoreceptor affinity, pEC and pK. The results are compatible with the hypothesis that at least the majority of α-autoreceptors belong to the α branch of the α-adrenoceptor tree, across mammalian or at least rodent and lagomorph species. [ABSTRACT FROM AUTHOR]
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Titel: |
Subclassification of presynaptic α-adrenoceptors: α-autoreceptors in rabbit atria and kidney.
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Autor/in / Beteiligte Person: | Limberger, Norbert ; Funk, Ludwig ; Trendelenburg, Anne-Uhike ; Starke, Klaus |
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Zeitschrift: | Naunyn-Schmiedeberg's Archives of Pharmacology, Jg. 352 (1995-07-01), Heft 1, S. 31-42 |
Veröffentlichung: | 1995 |
Medientyp: | academicJournal |
ISSN: | 0028-1298 (print) |
DOI: | 10.1007/BF00169187 |
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