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EFFECT OF al一 ADRENOCEPTOR SUBTYPES ON S-ADRENOCEPTOR MEDIATED POSITIVE INOTROPIC RESPONSE IN RAT LEFT ATRIA

ZHANG YOU-YI , YU GENG-SHENG , CHFNG MTNCi-ZHF ANT) HAN OT_DF (CHTT)F HAN

Section of Primates Cognitive Brain Research,Kunming Institute of Zoology,the Chinese Academy of Sciences.Kunming 650223,Yunnan

Abstract

The distribution of the #aLpha#l-adrenoceptor (#alpha#l-AR) subtypes and the effects of activation of al一AR subtypes on the#beta#adrenoceptor(#beta#AR) mediated positive inotropic response were investigated. The radioligand binding assays indicated that the Bmex and Kd
values were 11. 7士18 fmol/mg·protein and 8 6. 0士9. 6 pmol/L respectively. Pretreatment of the preparations with 20 }imol/L chloroethylclonidine (CEC) which inactivated a1#beta# subtype，decreased the B. to 45. 7士5. 2 fmol/mg·protein (P<0. 0l).
The inhibition curves of 5-methyl-urapidil were best fitted to two site model and indicated that a1A subtype took 28. 5%of total 12sIBE specific binding sites. In the functional experiments，norepinephrine (NE) induced a positive inotropic response in a concentration dependent manner by activation of both#beta#and #alpha#l-AR. The concentration-response curves (CRC) for NE were shifted rightward after the pretreatment of the preparations with 20 pmol/L CEC，but leftward in the presenece of I nmol/L WB4101. In the presence of 10 }tmol/L phentolamine which inactivated both #alpha#l-AR subtypes，the CRC for
NE were shifted leftward. When al一AR was activated by phenylephrine the CRC for isoproterenol (selective#beta#AR agonist) were shifted rightward. The results suggested that the #alpha#1#beta# subtype enhanced while the #alpha#1A subtype inhibited the (3-AR mediated positive inotropic response. When both alA and #alpha#1#beta# subtypes were activated simultaneously the #alpha#1A subtype show dominate role.

Key words: a,-adrenoceptor; ;S-adrenoceptor;;receptor subtype

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Citing This Article：

ZHANG YOU-YI , YU GENG-SHENG , CHFNG MTNCi-ZHF ANT) HAN OT_DF (CHTT)F HAN. EFFECT OF al一 ADRENOCEPTOR SUBTYPES ON S-ADRENOCEPTOR MEDIATED POSITIVE INOTROPIC RESPONSE IN RAT LEFT ATRIA. Acta Physiol Sin 1994; 46 (5): (in Chinese with English abstract).