Oxytocin receptors in sheep and rat myometrium : High or low affinity binding sites?

Pliška, V.; Heiniger, J. P.; Müller-Lhotsky, A; Ekberg, Björn

doi:10.1016/0022-4731(84)90696-4

Cited by 6 publications

(16 citation statements)

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“…It should be noted that the labelled myometrial oxytocin-receptor protein corresponds to a highaffinity binding site for oxytocin. Binding sites with medium affinity which may have a receptor function have been found on uterine cells from several other species [21]. The specific labelling of a myometrial oxytocin-receptor protein described in this report should be helpful for further structural investigations and for functional studies.…”

Section: Discussionmentioning

confidence: 67%

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Identification of a myometrial oxytocin‐receptor protein

Fahrenholz

Hackenberg

Muller

1988

European Journal of Biochemistry

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The specific binding of [3H]oxytoxin to uterine membrane peparations derived from different species at late pregnancy was examined. The highest receptor density (b,,, value) was found in membranes derived from the myometria of guinea pigs between day 60 post-conception (b,,, = 3.6 f 0.1 pmol/mg) and day 65 (b,,, = 4.4 f 0.1 pmol/mg). The similarity of & values for oxytocin binding (Kd = 2.6 f 0.2 nM) and for vasopressin binding (& = 2.1 f 0.4 nM) to the same membranes derived from a guinea pig myometrium indicate a homogenous population of high-affinity binding sites which do not discriminate between these two hormones.Competitive binding experiments with specific oxytocin agonists containing either sarcosine or N-methylalanine in the place of Pro' demonstrated that these myometrial receptors have the pharmacological properties of oxytocin receptors.The analogue of 1 -deamino-[8-lysine]vasopressin containing a photoreactive azidophenylamidino group at the sidechain of Lys' retained roughly the same receptor affinity as oxytocin. In photoaffinity labelling experiments with the tritium-labelled analogue a membrane protein from guinea pig myometrium with an apparent relative molecular mass M , of 78000 f 5000 (n = 13) was preferentially labelled. The labelling of this protein was completely suppressed by a 100-fold molar excess of either oxytocin, or [Sar7]oxytocin or [Thr4, Sar7]oxytocin, but not by other peptide hormones. These results provide evidence that the labelled 78000-M, protein is a myometrial oxytocin-receptor protein.The neurohypophysial nonapeptide oxytocin stimulates the contraction of smooth muscle cells in the myometrial layer of the uterus. The existence of specific oxytocin receptors has been demonstrated in the animal and human myometrium [l, 21. The oxytocin sensitivity of the uterus increases during pregnancy and is accompanied by an estrogen-induced increase in the concentration of myometrial oxytocin receptors at late pregnancy and at early-term labor [3 -51.The molecular events which are triggered after binding of oxytocin to its myometrial receptor are not well understood. There is evidence for inositol phosphate production [6] and for Ca2+ influx in the myometrium [7]. Furthermore, oxytocin has been shown to inhibit a (CaZ+ + MgZ+) ATPase [8] and to increase the intercellular communication via gap junctions [9].Little is known about the oxytocin receptor's physical properties. Soloff and Fernstrom were able to solubilize with a relatively low yield (20 -25%) oxytocin binding sites from the pregnant rat myometrium and the rat mammary gland with a zwitterionic detergent [lo]. Gel filtration analysis indicated that the solubilized oxytocin binding components from rat mammary gland were present in multiple molecular mass forms: M, values ranged from 40000 to greater than 200000. The uterine oxytocin-receptor protein, however, has not yet been identified. The present study was performed to identify myometrial oxytocin-receptor proteins. For this purpose, a myometrial membrane from guinea pig c...

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Section: Discussionmentioning

confidence: 67%

“…The existence of specific oxytocin receptors has been demonstrated in the animal and human myometrium [l, 21. The oxytocin sensitivity of the uterus increases during pregnancy and is accompanied by an estrogen-induced increase in the concentration of myometrial oxytocin receptors at late pregnancy and at early-term labor [3 -…”

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confidence: 99%

Identification of a myometrial oxytocin‐receptor protein

Fahrenholz

Hackenberg

Muller

1988

European Journal of Biochemistry

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“…Binding-site-af'nity spectrum of P. brassicae vesicles for iodinated toxin. The binding data were analyzed by the method described earlier [27]. Affinity spectrum [28]: relation between binding capacities (BmJ (nM) and dissociation constants (&) (nM).…”

Section: Resultsmentioning

confidence: 99%

“…Analogously to the procedure used for homologous ligands described in our previous communication [27], the dissociation constant for non-iodinated toxin (K') was determined in a competition experiment; the non-iodinated and iodinated toxin were considered as heterologous ligands. The transformation of the formula:…”

Section: Binding Assaymentioning

confidence: 99%

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Binding of the delta endotoxin from Bacillus thuringiensis to brush‐border membrane vesicles of the cabbage butterfly (Pieris brassicae)

Hofmann

Lüthy

Hütter

et al. 1988

European Journal of Biochemistry

230

117

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The insecticidal delta endotoxin of Bacillus thuringiensis was labeled with iodine-125. Brush-border membrane vesicles, prepared from the midgut epithelium of Pieris brassicae larvae, known to be highly susceptible to the toxin, and from a non-target tissue: the small intestine of rat, were examined for binding of '251-toxin. The toxin was bound specifically only to insect vesicles. Its binding to the insect membrane system was competitively inhibited by '271-toxin and non-iodinated toxin, whereas the binding of the 1251-toxin to the mammalian membrane system was not affected by unlabeled toxin. Vesicles of P. brassicae possess two individual bindingsite populations for iodinated toxin with dissociation constants of 46 nM and 490 nM. The Hill coefficients of both sites were approximately 1 and the binding capacities were 0.2 pmol and 30 pmol/mg vesicle protein for the high and the low-affinity sites respectively. The estimation of the dissociation constant for non-iodinated toxin, using a competition experiment, revealed only one binding-site population which possessed a dissociation constant of 235 nM. It is concluded that this is the binding site for the native toxin. This site was sensitive towards treatment with proteases or mixed glycosidases. It is suggested that it is a protein or a glycoprotein.The delta endotoxin of Bacillus thuringiensis is a proteinaceous, crystalline insecticide, toxic to the larval stages of several important pest insects in agriculture and forestry. The crystals are composed of subunits (protoxin) with a molecular mass of about 130 kDa [l -31. The toxic moiety is located on the N-terminal half of the protein [4-61 and has a molecular mass of approximately 60 -68 kDa. The molecular mass of the protoxin and that of the activated toxin vary depending on the strain and on the proteolytic procedure used for the activation. In the case of the strain studied here, activation of the protoxin (136 kDa) by trypsin leads to toxic fragments with molecular masses of 55 kDa and 70 kDa. In vitro the protoxin needs proteolytic activation to exhibit toxicity against insect cell cultures [7, 81. In vivo the protoxin is enzymatically activated within the digestive tract. Furthermore, the toxins of various strains differ in their host spectrum [9, 101. The delta endotoxin destroys the gut epithelia of susceptible insect larvae [ll]; the results of several studies have shown that the permeability of the gut membrane undergoes changes (for review, see [12]).

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Effect of Mg2+ on the binding of oxytocin to sheep myometrial cells

Pliška

Albertin

1991

Biochemical Journal

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Binding isotherms of oxytocin to sheep myometrial cells in a short-term cell culture were investigated in the presence of Mg2+ in the concentration range 0-10 mM. The occurrence of at least three binding sites had been demonstrated earlier. Mg2+ influences individual sites and individual features of the binding isotherm differently. Dissociation constants (Kd) of the high- and medium-affinity sites attain a minimum of 6.8 x 10(-10) and 4.2 x 10(-8) mol/l respectively at 2.75 mM-Mg2+. The two sites display the highest binding capacity (B) at 1 mM-Mg2+ (ratio of high affinity/medium affinity is 1:16). The B/Kd quotients reflecting relative binding (bound-to-free concentration) at the half-saturation of binding sites also have their maxima at 1 mM-Mg2+. The high-affinity site displays a strong positive co-operativity (Hill coefficient at 4 mM-Mg2+ of 2.4), which is amplified in the presence of Mg2+. Positive co-operativity of the medium-affinity site is markedly lower (Hill coefficient at 4 mM-Mg2+ of 1.5) and shows less dramatic Mg(2+)-dependence. Low-affinity sites are not co-operative at any Mg2+ concentration. It is concluded that Mg2+ may display its effect upon the oxytocin-receptor interaction predominantly by influencing positive co-operativity.

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Oxytocin receptors in sheep and rat myometrium : High or low affinity binding sites?

Cited by 6 publications

References 0 publications

Identification of a myometrial oxytocin‐receptor protein

Identification of a myometrial oxytocin‐receptor protein

Binding of the delta endotoxin from Bacillus thuringiensis to brush‐border membrane vesicles of the cabbage butterfly (Pieris brassicae)

Effect of Mg2+ on the binding of oxytocin to sheep myometrial cells

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