{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,2]],"date-time":"2025-11-02T16:18:23Z","timestamp":1762100303715},"reference-count":49,"publisher":"Wiley","issue":"3","license":[{"start":{"date-parts":[[2009,2,3]],"date-time":"2009-02-03T00:00:00Z","timestamp":1233619200000},"content-version":"vor","delay-in-days":4020,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":["bpspubs.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["British J Pharmacology"],"published-print":{"date-parts":[[1998,2]]},"abstract":"\n\nWe have recently suggested the existence in the heart of a \u2018putative \u03b24<\/jats:sub>\u2010adrenoceptor\u2019 based on the cardiostimulant effects of non\u2010conventional partial agonists, compounds that cause cardiostimulant effects at greater concentrations than those required to block \u03b21<\/jats:sub>\u2010 and \u03b22<\/jats:sub>\u2010adrenoceptors. We sought to obtain further evidence by establishing and validating a radioligand binding assay for this receptor with (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A ((\u2212)\u20104\u2010(3\u2010tertiarybutylamino\u20102\u2010hydroxypropoxy) benzimidazol\u20102\u2010one) in rat atrium. We investigated (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A for this purpose for two reasons, because it is a non\u2010conventional partial agonist and also because it is a hydrophilic radioligand.<\/jats:p><\/jats:list-item>\nIncreasing concentrations of (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A, in the absence or presence of 20\u2003\u03bcM<\/jats:sc> (\u2212)\u2010CGP 12177A to define non\u2010specific binding, resulted in a biphasic saturation isotherm. Low concentrations bound to \u03b21<\/jats:sub>\u2010 and \u03b22<\/jats:sub>\u2010adrenoceptors (pK<\/jats:italic>D<\/jats:sub> 9.4\u00b10.1, Bmax<\/jats:sub> 26.9\u00b13.1\u2003fmol\u2003mg\u20101<\/jats:sup> protein) and higher concentrations bound to the \u2018putative \u03b24<\/jats:sub>\u2010adrenoceptor\u2019 (pK<\/jats:italic>D<\/jats:sub> 7.5\u00b10.1, Bmax<\/jats:sub> 47.7\u00b14.9\u2003fmol\u2003mg\u22121<\/jats:sup> protein). In other experiments designed to exclude \u03b21<\/jats:sub>\u2010 and \u03b22<\/jats:sub>\u2010adrenoceptors, (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A (1\u2013200\u2003nM<\/jats:sc>) binding in the presence of 500\u2003nM<\/jats:sc> (\u2212)\u2010propranolol was also saturable (pK<\/jats:italic>D<\/jats:sub> 7.6\u00b10.1, Bmax<\/jats:sub> 50.8\u00b17.4\u2003fmol\u2003mg\u22121<\/jats:sup> protein).<\/jats:p><\/jats:list-item>\nThe non\u2010conventional partial agonists (\u2212)\u2010CGP 12177A (pK<\/jats:italic>i<\/jats:sub> 7.3\u00b10.2), (\u00b1)\u2010cyanopindolol (pK<\/jats:italic>i<\/jats:sub> 7.6\u00b10.2), (\u2212)\u2010pindolol (pK<\/jats:italic>i<\/jats:sub> 6.6\u00b10.1) and (\u00b1)\u2010carazolol (pK<\/jats:italic>i<\/jats:sub> 7.2\u00b10.2) and the antagonist (\u2212)\u2010bupranolol (pK<\/jats:italic>i<\/jats:sub> 6.6\u00b10.2), all competed for (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A binding in the presence of 500\u2003nM<\/jats:sc> (\u2212)\u2010propranolol at the \u2018putative \u03b24<\/jats:sub>\u2010adrenoceptor\u2019, with affinities closely similar to potencies and affinities determined in organ bath studies.<\/jats:p><\/jats:list-item>\nThe catecholamines competed with (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A at the \u2018putative \u03b24<\/jats:sub>\u2010adrenoceptor\u2019 in a stereoselective manner, (\u2212)\u2010noradrenaline (pK<\/jats:italic>i<\/jats:sub>H<\/jats:sub> 6.3\u00b10.3, pK<\/jats:italic>i<\/jats:sub>L<\/jats:sub> 3.5\u00b10.1), (\u2212)\u2010adrenaline (pK<\/jats:italic>i<\/jats:sub>H<\/jats:sub> 6.5\u00b10.2, pK<\/jats:italic>i<\/jats:sub>L<\/jats:sub> 2.9\u00b10.1), (\u2212)\u2010isoprenaline (pK<\/jats:italic>i<\/jats:sub>H<\/jats:sub> 6.2\u00b10.5, pK<\/jats:italic>i<\/jats:sub>L<\/jats:sub> 3.4\u00b10.1), (+)\u2010isoprenaline (pK<\/jats:italic>i<\/jats:sub><1.7), (\u2212)\u2010RO363 ((\u2212)\u2010(1\u2010(3,4\u2010dimethoxyphenethylamino)\u20103\u2010(3,4\u2010dihydroxyphenoxy)\u20102\u2010propranol)oxalate, pK<\/jats:italic>i<\/jats:sub> 5.5\u00b10.1).<\/jats:p><\/jats:list-item>\nThe inclusion of guanosine 5\u2010triphosphate (GTP 0.1\u2003mM<\/jats:sc>) had no effect on binding of (\u2212)\u2010CGP 12177A or (\u2212)\u2010isoprenaline to the \u2018putative \u03b24<\/jats:sub>\u2010adrenoceptor\u2019. In competition binding studies, (\u2212)\u2010CGP 12177A competed with (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A for one receptor state in the absence (pK<\/jats:italic>i<\/jats:sub> 7.3\u00b10.2) or presence of GTP (pK<\/jats:italic>i<\/jats:sub> 7.3\u00b10.2). (\u2212)\u2010Isoprenaline competed with (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A for two states in the absence (pK<\/jats:italic>i<\/jats:sub>H<\/jats:sub> 6.6\u00b10.3, pK<\/jats:italic>i<\/jats:sub>L<\/jats:sub> 3.5\u00b10.1; % H 25\u00b17) or presence of GTP (pK<\/jats:italic>i<\/jats:sub>H<\/jats:sub> 6.2\u00b10.5, pK<\/jats:italic>i<\/jats:sub>L<\/jats:sub> 3.4\u00b10.1; % H 37\u00b16). In contrast, at \u03b21<\/jats:sub>\u2010adrenoceptors, GTP stabilized the low affinity state of the receptor for (\u2212)\u2010isoprenaline.<\/jats:p><\/jats:list-item>\nThe specificity of binding to the \u2018putative \u03b24<\/jats:sub>\u2010adrenoceptor\u2019 was tested with compounds active at other receptors. High concentrations of the \u03b23<\/jats:sub>\u2010adrenoceptor agonists, BRL 37344 ((RR<\/jats:bold>+SS<\/jats:bold>)[4\u2010[2\u2010[[2\u2010(3\u2010chlorophenyl)\u20102\u2010hydroxy\u2003\u2010\u2003ethyl]amino]propyl]phenoxy]acetic acid, 6\u2003\u03bcM<\/jats:sc>), SR 58611A (ethyl{(7S<\/jats:bold>)\u20107\u2010[(2R<\/jats:bold>)\u20102\u2003\u2010\u2003(3\u2003\u2010\u2003chlorophenyl)\u2003\u2010\u20032\u2003\u2010\u2003hydroxyethylamino]\u2003\u2010\u20035,6,7,8\u2003\u2010\u2003tetrahydronaphtyl2\u2003\u2010\u2003yloxy} acetate hydrochloride, 6\u2003\u03bcM<\/jats:sc>), ZD 2079 ((\u00b1)\u20101\u2010phenyl\u20102\u2010(2\u20104\u2010carboxymethylphenoxy)\u2010ethylamino)\u2010ethan\u20101\u2010ol, 60\u2003\u03bcM<\/jats:sc>), CL 316243 (disodium (R<\/jats:bold>,R<\/jats:bold>)\u20105\u2010[2\u2010[2\u2010(3\u2010chlorophenyl)\u20102\u2010hydroxyethyl\u2010amino]propyl]\u2010 1,3\u2010benzodioxole\u20102,2\u2010dicarboxylate, 60\u2003\u03bcM<\/jats:sc>) and antagonist SR 59230A (3\u2010(2\u2010ethylphenoxy)\u20101\u2010[(1S<\/jats:bold>)\u20101,2,3,4\u2010tetrahydronaphth\u20101\u2010ylamino]\u20102S<\/jats:bold>\u20102\u2010propanol oxalate, 6\u2003\u03bcM<\/jats:sc>) caused less than 22% inhibition of (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A binding in the presence of 500\u2003nM<\/jats:sc> (\u2212)\u2010propranolol. Histamine (1\u2003mM<\/jats:sc>), atropine (1\u2003\u03bcM<\/jats:sc>), phentolamine (10\u2003\u03bcM<\/jats:sc>), 5\u2010HT (100\u2003\u03bcM<\/jats:sc>) and the 5\u2010HT4<\/jats:sub> receptor antagonist SB 207710 ((1\u2010butyl\u20104\u2010piperidinyl)\u2010methyl 8\u2010amino\u20107\u2010iodo\u20101,4\u2010benzodioxan\u20105\u2010carboxylate, 10\u2003nM<\/jats:sc>) caused less than 26% inhibition of binding.<\/jats:p><\/jats:list-item>\nNon\u2010conventional partial agonists, the antagonist (\u2212)\u2010bupranolol and catecholamines all competed for (\u2212)\u2010[3<\/jats:sup>H]\u2010CGP 12177A binding in the absence of (\u2212)\u2010propranolol at \u03b21<\/jats:sub>\u2010adrenoceptors, with affinities (pK<\/jats:italic>i<\/jats:sub>) ranging from 1.6\u20133.6 log orders greater than at the \u2018putative \u03b24<\/jats:sub>\u2010adrenoceptor\u2019.<\/jats:p><\/jats:list-item>\nWe have established and validated a radioligand binding assay in rat atrium for the \u2018putative \u03b24<\/jats:sub>\u2010adrenoceptor\u2019 which is distinct from \u03b21<\/jats:sub>\u2010, \u03b22<\/jats:sub>\u2010 and \u03b23<\/jats:sub>\u2010adrenoceptors. The stereoselective interaction with the catecholamines provides further support for the classification of the receptor as \u2018putative \u03b24<\/jats:sub>\u2010adrenoceptor\u2019.<\/jats:p><\/jats:list-item>\n<\/jats:list>\n<\/jats:p>British Journal of Pharmacology<\/jats:italic> (1998) 123<\/jats:bold>, 371\u2013380; doi:10.1038\/sj.bjp.0701609<\/jats:ext-link><\/jats:p>","DOI":"10.1038\/sj.bjp.0701609","type":"journal-article","created":{"date-parts":[[2005,1,28]],"date-time":"2005-01-28T19:19:31Z","timestamp":1106939971000},"page":"371-380","update-policy":"http:\/\/dx.doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":43,"title":["Validity of (\u2212)\u2010[3<\/sup>H]\u2010CGP 12177A as a radioligand for the \u2018putative \u03b2<\/i>4<\/sub>\u2010adrenoceptor\u2019 in rat atrium"],"prefix":"10.1111","volume":"123","author":[{"given":"Doreen","family":"Sarsero","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Peter","family":"Molenaar","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alberto J.","family":"Kaumann","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2009,2,3]]},"reference":[{"key":"e_1_2_6_2_1","doi-asserted-by":"publisher","DOI":"10.1002\/med.2610130604"},{"key":"e_1_2_6_3_1","doi-asserted-by":"publisher","DOI":"10.1097\/00005344-198305000-00013"},{"key":"e_1_2_6_4_1","doi-asserted-by":"publisher","DOI":"10.1172\/JCI118783"},{"key":"e_1_2_6_5_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1476-5381.1994.tb13167.x"},{"key":"e_1_2_6_6_1","doi-asserted-by":"publisher","DOI":"10.1016\/0024-3205(72)90133-6"},{"key":"e_1_2_6_7_1","doi-asserted-by":"publisher","DOI":"10.1016\/0006-2952(73)90196-2"},{"key":"e_1_2_6_8_1","doi-asserted-by":"publisher","DOI":"10.1111\/j.1476-5381.1995.tb13223.x"},{"key":"e_1_2_6_9_1","first-page":"1000","article-title":"Beta\u20103 adrenoceptor selectivity of the dioxolane dicarboxylate phenethanola\u2010mines","volume":"269","author":"Dolan J.A.","year":"1994","journal-title":"J. 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