Receptors for neurohypophyseal hormones along the rat nephron: 125I-labelled d(CH2)5[Tyr(Me)2, Thr4, Orn8, Tyr-NH(2)9] vasotocin binding in microdissected tubules.
A microassay was developed to measure the binding of the labelled monoiodinated analogue [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-O-methyltyrosine, 4-threonine, 8-ornithine, 9-125I-tyrosylamide]vasotocin [125I-d(CH2)5[Tyr (Me)2, Thr4, Tyr-NH(2)9]OVT] to isolated nephron segments microdissected from collagenase-treated rat kidneys. When determined using 1.7 nM labelled ligand at 4 degrees C, specific binding sites (expressed at 10(-18) mol 125I-d(CH2)5[Tyr (Me)2, Thr4, Tyr-NH(2)9]OVT bound/mm tubule length) were found in medullary thick ascending limbs (MTAL), 1.67 +/- 0.49; cortical thick ascending limbs, 2.20 +/- 0.80; cortical collecting ducts, 2.39 +/- 0.86; outer medullary collecting ducts (OMCD), 2.54 +/- 0.53 and inner medullary collecting ducts, 5.33 +/- 0.40, whereas no specific binding could be detected in glomeruli and proximal tubules. Specific 125I-d(CH2)5[Tyr (Me)2, Thr4, Tyr-NH(2)9]OVT binding to OMCD was saturable with incubation time and reversible after elimination of free labelled ligand (the association and dissociation rate constants at 4 degrees C were 1.06 x 10(7) M-1 min-1 and 1.95 x 10(-2) min-1 respectively). The stereospecificity of MTAL and OMCD binding sites was assessed in competitive experiments revealing the following recognition pattern for a series of eight vasopressin analogues:dDAVP greater than AVP greater than d(CH2)5-[Tyr (Me)2, Thr4, Tyr-NH(2)9]OVT = AVT = OT greater than d(CH2)5[Tyr(Me)2]AVP = [Thr4, Gly7]OT greater than [Phe2, Orn8]VT, whereas pharmacological concentrations of insulin and glucagon did not impair radioligand binding. These results indicate that the detected labelled binding sites might correspond mainly to physiological V2 vasopressin receptors.
Ammar
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A
Laboratoire de Physiologie Cellulaire, URA n.219 du CNRS, Collège de France, Paris.
Schmidt
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A
Semmekrot
B
B
Roseau
S
S
Butlen
D
D
D000818:Animals; D001667:Binding, Competitive; D007457:Iodine Radioisotopes; D007672:Kidney Cortex / Q000378:metabolism; D007679:Kidney Medulla / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000378:metabolism; D007686:Kidney Tubules, Distal / Q000378:metabolism; D007700:Kinetics; D008297:Male; D009399:Nephrons / Q000378:metabolism*; D010121:Oxytocin / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011945:Receptors, Angiotensin / Q000378:metabolism*; D017483:Receptors, Vasopressin; D014667:Vasopressins / Q000378:metabolism
D007457:Iodine Radioisotopes; C055830:KB 5-21; D011945:Receptors, Angiotensin; D017483:Receptors, Vasopressin; D014667:Vasopressins; D010121:Oxytocin