Ligand- and Subtype-Selective Coupling of HumanAlpha-2 Adrenoceptors to Ca++ elevation in Chinese Hamster Ovary Cells1
- 1Department of Physiology, Uppsala University, Uppsala, Sweden (J.P.K., R.S., K.E.O.A.) and 2Department of Biochemistry and Pharmacy, Åbo Akademi University, Turku, Finland (J.P.K., A.R.)
Abstract
The agonist profiles for Ca++ elevations mediated by the human alpha-2 adrenoceptor subtypes alpha-2A,alpha-2B and alpha-2C were compared in the clones of Chinese hamster ovary cells expressing comparable numbers of receptors. No difference was seen between the different clones with respect to the maximum Ca++ mobilizations or the concentrations producing half-maximal stimulation in response to noradrenaline. Ca++ elevations were sensitive to phospholipase C inhibitor U-73122 (1-[6-([17β]-3-methoxyestra-1,3,5[10]-trien-17-yl)aminohexyl]-1H-pyrrole-2,5-dione) and pertussis toxin-pretreatment. Although noradrenaline was equally potent and active in all the clones, marked differences in the response to the other agonists were seen. UK14,304 (5-bromo-N-[4,5-dihydro-1H-imidazol-2-yl]-6-quinoxalinamine) was a full agonist (when compared to noradrenaline) for alpha-2A and alpha-2C, d-medetomidine ([+]-[S]-[4-(1-[2,3-dimethylphenyl]ethyl)-1H-imidazole]HCl) was a full agonist for alpha-2B and alpha-2C and oxymetazoline (3-[(4,5-dihydro-1H-imidazol-2-yl-)methyl]-6-[1,1-dimethylethyl]-2,4-dimethylphenol HCl) was a full agonist only for alpha-2B receptors. Clonidine (2-[2,6-dichloroaniline]-2-imidazoline HCl) was a partial agonist in all the cases; almost no response to this ligand was obtained in the alpha-2B-expressing cells. When the Ca++ responses are compared to the previously published results on cAMP inhibition in Chinese hamster ovary cells, clonidine seems to be significantly less efficacious in elevating Ca++ than in decreasing cAMP.
Footnotes
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Send reprint requests to: Dr. Jyrki Kukkonen, Department of Physiology, Uppsala University, BMC, P.O. Box 572, S-75123 Uppsala, Sweden.
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↵1 This study was supported by The Technology Development Center of Finland, The Magnus Ehrnrooth Foundation, The Medical Research Council of Sweden and The Cancer Research Fund of Sweden.
- Abbreviations:
- [Ca++]i
- intracellular free [Ca++]
- CHO
- Chinese hamster ovary
- clonidine
- 2-(2,6-dichloroaniline)-2-imidazoline HCl
- Δ[Ca++]
- elevation of intracellular free [Ca++] (= [Ca++]i/stimulated − [Ca++]i/basal)
- Δ[Ca++]max
- maximum elevation of intracellular free [Ca++]
- d-medetomidine
- [+]-[S]-(4-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole)HCl
- EC50
- concentration producing half-maximal response
- EGTA
- ethylene glycol-bis(β-aminoethyl ether) N,N,N′,N′-tetraacetic acid
- oxymetazoline
- 3-([4,5-dihydro-1H-imidazol-2-yl-]methyl)-6-(1,1-dimethylethyl)-2,4-dimethylphenol HCl
- probenecid
- p-(dipropylsulfamoyl)benzoic acid
- TBM
- TES buffered medium
- TES
- 2-([2-hydroxy-1,1-bis(hydroxymethyl)ethyl]amino) ethane sulfonic acid
- UK14
- 304, 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine
- U-73122
- 1-(6-[(17β)-3-methoxyestra-1,3,5(10)-trien-17-yl]aminohexyl)-1H-pyrrole-2,5-dione
- U-73343
- 1-(6-[(17β)-3-methoxyestra-1,3,5(10)-trien-17-yl]aminohexyl)-2,5-dione
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- Received March 30, 1998.
- Accepted June 23, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
