ISSN:
1432-1912
Keywords:
Human cardiac muscarinic cholinoceptors
;
Muscarinic cholinoceptor subtypes
;
Human right atrium
;
Human left papillary muscle
;
Negative inotropic effect
;
[N-Methyl-3H]-scopolamine
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary In human atrial and ventricular myocardium, the muscarinic cholinoceptor (M-cholinoceptor) populations were characterized by means of radioligand binding (with [N-methyl-3H]-scopolamine ([3H]-NMS) as the ligand) and functional experiments (negative inotropic effect of carbachol on isolated electrically driven right atrial and left papillary muscle preparations). (1) Binding of [3H]-NMS to human atrial and ventricular membranes was rapid, reversible and saturable (KD-values: 0.5–1.0 nmol/l). The maximal number of [3H]-NMS binding sites, however, was approximately 2.5-fold higher in right and left atrial membranes (200–250 fmol[3H]-NMS specifically bound/mg protein) than in right and left ventricular membranes (80–100 fmol/mg protein). (2) M-cholinoceptor antagonists inhibited [3H]-NMS binding to right atrial and left ventricular membranes with steep, monophasic competition curves indicating interaction with a single class of binding sites. In both tissues the order of potency was: atropine 〉 AF-DX 116 〉 hexahydro-siladifenidol (HHSiD) 〉 pirenzepine. (4) It is concluded that, in the human heart, functional M-cholinoceptors mediating negative inotropic effects exist that belong predominantly (if not exclusively) to the M2-subtype. However, the atrial regions of the human heart are more densely endowed with these M2-cholinoceptors than the ventricular myocardium.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00195052
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