Interactions of Glucagon, Gut Glucagon, Vasoactive Intestinal Polypeptide and Secretin with Liver and Fat Cell Plasma Membranes: Binding to Specific Sites and Stimulation of Adenylate Cyclase1

1. A rapid method for the isolation of hormonally sensitive rat fat-cell plasma membranes was developed by using immunological techniques. 2. Rabbit anti-(rat erythrocyte) sera were raised and shown to cross-react with isolated rat fat-cells. 3. Isolated rat fat-cells were coated with rabbit anti-(rat erythrocyte) antibodies, homogenized and the homogenate made to react with an immunoadsorbent prepared by covalently coupling donkey anti-(rabbit globulin) antibodies to aminocellulose. Uptake of plasma membrane on to the immunoadsorbent was monitored by assaying the enzymes adenylate cyclase and 5′-nucleotidase and an immunological marker consisting of a 125I-labelled anti-(immunoglobulin G)-anti-cell antibody complex bound to the cells before fractionation. Contamination of the plasma-membrane preparation by other subcellular fractions was also investigated. 4. By using this technique, a method was developed allowing 25-40% recovery of plasma membrane from fat-cell homogenates within 30 min of homogenization. 5. Adenylate cyclase in the isolated plasma-membrane preparation was stimulated by 5 μm-adrenaline.

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Magnesium ion exerts a central role in the regulation of inhibitory adenosine receptors

Biochemical Journal ◽

10.1042/bj2290091 ◽

1985 ◽

Vol 229 (1) ◽

pp. 91-100 ◽

Cited By ~ 21

Author(s):

S M Yeung ◽

L H Fossom ◽

D L Gill ◽

D M Cooper

Keyword(s):

Dissociation Constant ◽

Plasma Membranes ◽

Alkylating Agents ◽

Regulatory Protein ◽

Agonist Binding ◽

Fat Cell ◽

Cation Site ◽

Bivalent Cation ◽

Cell Plasma ◽

Highly Sensitive

Guanine nucleotides and Mg2+ differentially regulate agonist binding to adenosine (Ri) receptors in fat-cell plasma membranes. GTP alone decreases binding of the agonist ligand [3H]N6-cyclohexyladenosine (CHA) by increasing the dissociation constant (Kd). Mg2+ alone also decreases [3H]CHA binding, which is associated with a decrease in the number of receptors and in the dissociation constant. In the presence of Mg2+, the effect of GTP is to increase [3H]CHA binding by increasing the total number of receptors. It thus appears that Mg2+ acts specifically at a bivalent-cation site which, with GTP, regulates agonist binding. This putative Mg site is highly sensitive to alkylating agents. Mild treatment with N-ethylmaleimide (NEM) abolishes the characteristic GTP effect on agonist binding in the presence of Mg2+. In addition, the effect of Mg2+ alone is also eliminated. The effect of GTP alone is largely unaltered. Studies of the adenylate cyclase activity indicate that this NEM treatment also abolishes the inhibition of basal activity by adenosine analogues, whereas guanylyl imidodiphosphate inhibition of forskolin-stimulated activity is only slightly impaired at this NEM concentration. These observations indicate that a Mg2+ ‘site’ or ‘component’ is required for the integration of receptor (Ri) occupancy with regulation of catalytic activity (C). The regulatory role of Mg2+ is more demonstrable in receptor-GTP-regulatory-protein (Ri-Ni) interactions than in GTP-regulatory-protein-catalytic-unit (Ni-C) interactions.

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Stimulation of Serotonin-N-Acetyltransferase Activity in the Pineal Gland of the Mongolian Gerbil (Meriones unguiculatus) by Intracerebroventricular Injection of Vasoactive Intestinal Polypeptide

Journal of Pineal Research ◽

10.1111/j.1600-079x.1989.tb00914.x ◽

1989 ◽

Vol 7 (4) ◽

pp. 393-399 ◽

Cited By ~ 9

Author(s):

Hannsjörg Schröder ◽

Jörg Stehle ◽

Morten Møller

Keyword(s):

Pineal Gland ◽

Vasoactive Intestinal Polypeptide ◽

Mongolian Gerbil ◽

Meriones Unguiculatus ◽

Intracerebroventricular Injection ◽

Acetyltransferase Activity ◽

Stimulation Of ◽

Intestinal Polypeptide

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Effects of tactile and electrical stimuli upon release of vasoactive intestinal polypeptide in the mammalian penis

Journal of Endocrinology ◽

10.1677/joe.0.1000249 ◽

1984 ◽

Vol 100 (2) ◽

pp. 249-252 ◽

Cited By ~ 23

Author(s):

A. F. Dixson ◽

K. M. Kendrick ◽

M. A. Blank ◽

S. R. Bloom

Keyword(s):

Vasoactive Intestinal Polypeptide ◽

Tactile Stimulation ◽

Fold Increase ◽

Sooty Mangabey ◽

Blood Samples ◽

Barbary Sheep ◽

Tactile Stimuli ◽

Potent Vasodilator ◽

Stimulation Of ◽

Intestinal Polypeptide

ABSTRACT Plasma levels of vasoactive intestinal polypeptide (VIP) in the corpora cavernosa penis and dorsal penile veins greatly exceeded those measured in the limb or caudal veins during anaesthesia in various mammals (Bennett's wallaby, Barbary sheep, cheetah, puma, sooty mangabey, pigtail macaque and chimpanzee). Tactile stimulation of the penis immediately before or during collection of blood samples resulted in an increase. In the wallaby, VIP levels (mean ± s.e.m.) in blood samples collected from the flaccid penis in the absence of tactile stimulation were very low (0·6 ± 0·5 pmol/l). A 36-fold increase in VIP occurred after manual extension of the flaccid penis (24·8 ± 3·2 pmol/l) or during manually stimulated erections (25· 1 ± 1·7 pmol/l). Electrical stimulation of erection produced no significant increase in VIP levels (2·3±0·9 pmol/l) unless accompanied by tactile stimulation (17·5±1·4 pmol/l). These studies provide the first demonstration that sensory feedback from the penis plays an important role in regulating vasoactive intestinal polypeptidergic activity. Since VIP is a potent vasodilator its release due to tactile stimuli during copulation may play a role in the maintenance of penile erection. J. Endocr. (1984) 100, 249–252

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