'These results indicate that dirnis~ished responsiveness of the aged hcart to vagiai stitnulation ancl exogenous2y adrnit~istered cholinergic agents reported in ...
Effects uf age on muscarinic cholinergic receptors in rat myocardium NJANOOK NARAYANAN A1611 90-ANNEDI-KBY L)c~p(ar/nic~i~~ c?j' Physiology, Col/rgr (f Mcdic.irzcj, Iliii~~c~r.sir~ of S~lskcrtc-he~z-vtir. Strsktrroon, 5";'i.v.k., ('trtrcitkr S7A1O M/O
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Received July 8, 1082 NARAYIZNAN, N.,;ti~dJ . - A . DERBY.1983. Effects of age on rnuscarinic cholincrpic rcccptors in r:it rnyocardiunl. Can. J . I'hysiol. Pharn.eaccr1. 6L: 822--829. Atrial and vcntricialar myocardium from young (3-4 monlhs old), young achalt (7-- 8 months oic!), and aged (24--25 n~onths trftl) rats wcrc used to study the influence of age on ci~rdiaccholia~ergicnluscarinic receptors. The cfensity of' niuscarinic receptors (cxprcssed as frnoi/rng protcin or pmol/p tissrre), detcrrriincti by the specific binding of 1 ' ~ j q u i n u c l i d i n ~ bcnzylate l ( [ ' H ] Q N B ~ )was , significantly greater (24-29(i%) in atria of aged rats comparcil with that in atrin of young or young adult rats. Thc mrascarinic rcceptor density in veratricles was found to be essentially similar in all aye groups studiect. Antagonist :as well its agonist binding chariacacrisaics of rnuscaria~icreceptor sites wera: cxarpiinccl in atria ancl ventricles from young :snd aged rats. N o significant age-related diffcrctrce was ubservcd in tlrc dissociation constant (K,,i of atrial or \~cntricularreceptors for the ;rntragonist ligantf [ ' H ~ Q N B(KI, npparent (nMj: 1.04 t 0. I6 and 0.98 i 0.12. respectively. for young and aged atria; 0.95 -t 0.08 and 0.76 -t- 0.10, respectively, for young and iigstl ventricles). SirniEarly, the conccntrations of tnuscarinic antagonist atropine andl agorlist ctirbachol c:iusirpg 50% inhibition of ( ' H J Q N B binding ro the receptor sites (ICs,,)in atria rind ~ientricles were not ;altcreci by age. Age-related difference was also not evident ill the Hill coefficients ti)r [ ' H I Q N w , atropine, 2nd c:ar$achol. 'These results indicate that dirnis~ishedresponsiveness of the aged hcart to vagiai stitnulation ancl exogenous2y adrnit~isteredcholinergic agents reported in the literatiarc cannot he attributed to an age-relateti rcdnctioa~in the nurnhcr of cardiac muscarielic reccptors or their affinities toward agowisa or hntayonist ligalads.
NAKAYANAN, N . . et J.-A. DERBY.198:a. EfCcc~sof age on mitsc:arinic cholinee-gicreceptors in rat myocardium. Can. J . Physiol. Pharnaacol. 61: X22-M2Cl. (In a utiIis6 Ic rnyocardc ailricu8airc et ventriculaire dc jeuncs rats ( 3 --4 noi is), de jcunes rats adultes (7--8 noi is) ct de rats AgCs (24-25 rnois) pour dvaluer B'inf'luencc de l'2ge sisr les rCce~?tei~rs rnuscariniclucs chc,lincrgic\ucs cardB;~cjues.La densit6 des rCceptcurs rni~scariniqu~ (exprin~Ceen f'rnol/rng cic prot6ilsc ou en prnol/g de tissu), dChcrmint2e par Ia fixation spkcifiatue du [3HJbcn~yIatc quinuclidinyl (['WIQNB), fut significativelncnt plus grande (24--2Cd4;/c)clans les oreillcttes des rats ig6s yue dans cclles des jcunes rats ct des jeunes rats adulrcs. Ida densit6 des r6cepteurs rnuscariniclucs dcs ventricules Ctait sirniIairc dans tous les groupes examines. On a examin2 les caractdristic~uesde fixation dcs antagonistes et cles agornihtcs cies sites rCcepacurs rr-arascrariniqucs. clans les orcillettes des rats jcuracs et 2gCa. Om ra'a ot~servdaucune diffCrencc significittivc, relice li I'rige, aians la constante de dissociation ( K o i tfcr riccptcurs auriculaires ou vcnt~iculaircs.pour le cot~r
