Characterization of muscarinic receptors in rat kidney.
Muscarinic receptors in mammalian kidney seem to be involved in diuresis. In this study we give a detailed characterization of receptors in rat kidney. Specific binding of [3H](-)-quinuclidinylbenzilate ([3H]QNB) to membranes of rat kidney cortex was saturable and of high affinity. A dissociation constant of 0.063 +/- 0.003 nM and a receptor density of 1.46 +/- 0.07 pmol/g wet weight were obtained. The dissociation kinetics could be best described by assuming a mono-exponential function (k-1 = (0.52 +/- 0.1) x 10(-4) s-1). The binding of [3H]QNB reached a maximum in 60 min at 0.6 nM at 37 degrees C. Competition experiments with the enantiomers of benzetimide confirmed the muscarinic nature of the [3H]QNB binding sites. The inhibition constants of pirenzepine (0.23 +/- 0.02 microM), (+-)-hexahydrosiladifenidol (0.040 +/- 0.002 microM), AF-DX 116 (1.45 +/- 0.07 microM), methoctramine (1.67 +/- 0.02 microM) and gallamine (78 +/- 3 microM) classified this receptor as an M3 receptor. Inhibition of [3H]QNB binding by the agonists methylfurtrethonium, arecoline, isoarecoline methiodide, arecaidine propargyl ester and McN-A-343 displayed monophasic inhibition curves. With (+/-)-cis-2-methyl-4-dimethylaminomethyl-1,3- dioxolane methiodide in two out of four experiments a small (11%) population of high affinity agonist sites could be detected. The potassium sparing diuretic amiloride inhibited [3H]QNB binding (36 +/- 3 microM). Although in a way related to the amiloride binding site, the muscarinic receptors in rat kidney are unlikely to be the primary target of diuretic action of this drug.
Blankesteijn
W M
WM
Department of Pharmacology, University of Nijmegen, Netherlands.
Siero
H L
HL
Rodrigues de Miranda
J F
JF
van Megen
Y J
YJ
Russel
F G
FG
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001667:Binding, Competitive; D066298:In Vitro Techniques; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D010277:Parasympathomimetics / Q000378:metabolism / Q000494:pharmacology; D011813:Quinuclidinyl Benzilate / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000378:metabolism / Q000502:physiology*
D010277:Parasympathomimetics; D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate; D000584:Amiloride