PT  - JOURNAL ARTICLE
AU  - Sandeep Rathi
AU  - Shiva Kazerounian
AU  - Kuldip Banwait
AU  - Stephanie Schulz
AU  - Scott A. Waldman
AU  - Satish Rattan
TI  - Functional and Molecular Characterization of β-Adrenoceptors in the Internal Anal Sphincter
AID  - 10.1124/jpet.102.048462
DP  - 2003 May 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 615--624
VI  - 305
IP  - 2
4099  - http://jpet.aspetjournals.org/content/305/2/615.short
4100  - http://jpet.aspetjournals.org/content/305/2/615.full
SO  - J Pharmacol Exp Ther2003 May 01; 305
AB  - The purpose of the present study was to characterize different β-adrenoceptors (β-ARs) and determine their role in the spontaneously tonic smooth muscle of the internal anal sphincter (IAS). The β-AR subtypes in the opossum IAS were investigated by functional in vitro, radioligand binding, Western blot, and reverse transcription-polymerase chain reaction (RT-PCR) studies. ZD 7114 [(S)-4-[2-hydroxy-3-phenoxypropylaminoethoxy]-N-(2-methoxyethyl)phenoxyacetamide], a selective β3-AR agonist, caused a potent and concentration-dependent relaxation of the IAS smooth muscle that was antagonized by the β3-AR antagonist SR 59230A [1-(2-ethylphenoxy)-3-[[(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]-(2S)-2-propanol hydrochloride]. Conversely, the IAS smooth muscle relaxation caused by β1- and β2-AR agonists (xamoterol and procaterol, respectively) was selectively antagonized by their respective antagonists CGP 20712 [(±)-2-hydroxy-5-[2-[[2-hydroxy-3-[4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]phenoxy]propyl]amino]ethoxy]-benzamide methanesulfonate salt] and ICI 118551. Saturation binding of [125I]iodocyanopindolol to β-AR subtypes revealed the presence of a high-affinity site (Kd1 = 96.4 ± 8.7 pM;Bmax1 = 12.5 ± 0.6 fmol/mg protein) and a low-affinity site (Kd2 = 1.96 ± 1.7 nM; Bmax2 = 58.7 ± 4.3 fmol/mg protein). Competition binding with selective β-AR antagonists revealed that the high-affinity site correspond to β1/β2-AR and the low affinity site to β3-AR. Receptor binding data suggest the predominant presence of β3-AR over β1/β2-AR. Western blot studies identified β1-, β2-, and β3-AR subtypes. The presence of β1-, β2-, and β3-ARs was further demonstrated by mRNA analysis using RT-PCR. The studies demonstrate a comprehensive functional and molecular characterization of β1-, β2-, and β3-ARs in IAS smooth muscle. These studies may have important implications in anorectal and other gastrointestinal motility disorders. The American Society for Pharmacology and Experimental Therapeutics