ISSN:
1432-1912
Keywords:
5-Hydroxytryptamine (5-HT, serotonin)
;
5-HTID receptors
;
MDCK cells
;
Cyclic AMP
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract 5-Hydroxytryptamine 5-HT1B/5-HT1D receptors are members of the same receptor subfamily, but display a different pharmacology (Hartig et al. (1992) Trends Pharmacol Set 13:152–159). Whereas several cell lines have been reported to contain 5-HT1B receptors, none has been described, however, that endogenously expresses well-characterized 5-HT1D receptors. The present study deals with the identification of 5-HT1D receptors inhibiting cyclic AMP accumulation in Madin-Darby canine kidney (MDCK) cells. 5-HT (1 nM− 10 μM) induced a concentration-dependent inhibition of the cyclic AMP accumulation stimulated by prostaglandin E1 (1 μM) in MDCK cells. The maximal effect of 5-HT averaged 50% inhibition and was abolished after a pre-treatment of the cells with pertussis toxin. Other agonists mimicked the effects of 5-HT, with the following rank order of potency (pEC50 ± SEM, n ≥ 3): 5-carboxamidotryptamine (8.36 ± 0.48) 〉 PAPP (p-aminophenylethyl-m-trifluoromethylphenyl piperazine, 7.89 ± 0.23) 〉 5-HT (7.35 ± 0.05) 〉 sumatriptan (6.65 ± 0.27). PAPP behaved as a partial agonist. 8-OH-DPAT (8-hydroxy-2(di-n-propylamino)tetralin) was less potent, its maximal effect being not reached at 0.1 mM. Methiothepin, GR127935, (−)propranolol, rauwolscine and ketanserin were all devoid of intrinsic activity (up to 10 μM or 0.1 mM). Methiothepin (10 nM, 0.1 μM and 1 μM) antagonized 5-HT effect (pA2 8.57 ± 0.44, Schild slope 1.17 ± 0.21, n = 3). GR127935 (1 nM, 10 nM and 0.1 μM) shifted the curve of 5-HT to the right, but the antagonism was not fully surmountable (apparent pKB value, 9.80 ± 0.16, n = 9). From the shifts obtained with rauwolscine (1 μM) and (−)propranolol (10 μM), respective pKB values were estimated 6.68 ± 0.30 and ≈ 5.4 (n = 3 each). PAPP, when tested as an antagonist at 1 μM, also shifted the curve of 5-HT to the right, with a pKB of 8.27 ± 0.16 (n = 3). Finally, ketanserin (10 μM) also antagonized the effects of 5-HT, the pKB being 6.54 ± 0.16 (n = 9). The rank orders of agonist and antagonist potencies strongly suggest 5-HT receptors mediating inhibition of cyclic AMP accumulation in MDCK cells to be 5-HT1D receptors. This is the first report of a cell line expressing endogenous, well-characterized, 5-HT1D receptors. With regard to the 5-HT1D receptor subtype involved, the relatively high potency of ketanserin would suggest it to be a 5-HT1Dα subtype or a mixture of 5-HT1Dα/5-HT1D\ subtypes. However, caution must be exercised here, owing to the poor knowledge of canine 5-HT1D receptor subtypes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00168555
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