Effects Of Guanosine Triphosphate Research Articles

A postsynaptic G-protein in hippocampal long-term potentiation

The effects of guanosine triphosphate (GTP)-binding protein (G-protein) blockade on hippocampal LTP at stratum radiatum-CA1 synapses was studied. Bath application of 20 mM lithium chloride (LiCl) inhibited long-term potentiation (LTP) of extracellularly-recorded excitatory postsynaptic potentials (EPSPs). Inclusion of 100 mM LiCl in intracellular recording electrodes was shown to block postsynaptic G-proteins by bath-application of baclofen, an agonist at the G-protein linked γ-aminobutyric acid (GABAB) receptor. Under normal conditions, GABAB receptor activation causes a hyperpolarization postsynaptically, and a decrease in neurotransmitter release presynaptically. With LiCl in the recording electrodes, the postsynaptically-mediated hyperpolarization was blocked, while the presynaptically-mediated depression of EPSPs was unaffected. With postsynaptic G-proteins blocked in this manner, LTP at these synapses was inhibited. These studies provide evidence for the involvement of a postsynaptic G-protein in LTP of stratum radiatum-CA1 synapses.

Differential response to gonadotropins and prostaglandin E2 in ovarian tissue during prenatal and postnatal development in cattle.

In cattle, growing follicles are present in fetal ovaries during the last part of gestation. This study examines the extent of changes in basal and hormone-stimulated adenylyl cyclase (AC) activity in ovaries of the bovine fetus when the first follicles begin to grow. The first growing follicles appeared in fetal ovaries around Day 180 and consisted mainly of primary and secondary follicles; few antral follicles were present before Day 220 of gestation. Basal AC activity in ovarian membranes increased simultaneously with the beginning of follicle growth in the fetus (5.8 +/- 0.9 vs. 9.3 +/- 1.3 pmol cAMP/mg protein/min at 130-180 and 180-210 days of gestation, respectively p less than 0.05). During the same time period, there was a significant increase in both the absolute (16.1 +/- 1.2 to 39.9 +/- 1.4 pmol cAMP/mg protein/min) and the relative (2.8 +/- 0.1 to 4.3 +/- 0.3 times the basal level, p less than 0.05) effects of guanosine triphosphate (GTP). After birth, basal and GTP-stimulated AC activities (pmol cAMP/mg protein/min) increased markedly in ovarian membranes of 1-wk-old calves and then decreased with age; the lowest levels were measured in mature cyclic cows. However, the relative effect of GTP (times the basal level) did not show this age-related variation. Prostaglandin E2 (PGE2) stimulation of AC in ovarian membranes from fetuses was high even on Day 120 (2.1 +/- 0.3 times the control level).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of guanosine nucleotides on skinned smooth muscle tissue of the rabbit mesenteric artery.

1. Effects of guanosine triphosphate (GTP) and guanosine 5'-o-(3-thio)triphosphate (GTP gamma S) on mechanical properties of skinned smooth muscle tissues of the rabbit mesenteric artery were investigated. 2. In skinned muscle tissues prepared by saponin, GTP (above 100 microM) and GTP gamma S (above 1 microM) enhanced the Ca2+-induced contraction (0.3 microM-Ca2+ buffered with 2 mM-EGTA) in the presence of 1 microM-ionomycin, a depletor of stored Ca2+. The concentration-response (pCa-tension) relationship observed in the presence of 10 microM-GTP gamma S shifted to the left with no change in the maximum response evoked by 10 microM-Ca2+. The action of GTP was reversible but that of GTP gamma S was not. 3. The enhancement of the Ca2+-induced contraction by GTP gamma S occurred with increases in the phosphorylation of myosin light chain and in the shortening velocity as measured with the slack test. 4. GTP gamma S had no effect on the Ca2+-independent contraction of skinned muscle tissues evoked by MgATP in Ca2+-free solution (4 mM-EGTA), following treatment with rigor solution containing adenosine 5'-o-(3-thio)triphosphate (ATP gamma S). 5. The present results indicate that GTP and GTP gamma S enhance the Ca2+-induced contraction in skinned muscle tissues due to increase in the Ca2+ sensitivity of contractile proteins. These enhancing actions of guanosine nucleotides on contractile proteins are discussed in comparison to those of protein kinase C.

Regulation of guinea pig myometrial beta-adrenoreceptors by guanosine triphosphate and magnesium ion.

The effects of guanosine triphosphate (GTP) and magnesium on the interaction of 1-isoproterenol with beta-adrenoreceptors were studied in myometrial membranes from nonpregnant and late-pregnant (0.9 gestation, term 65 days) guinea pigs. The affinity of the beta-adrenoreceptor for 1-isoproterenol, as measured by inhibition of (-)125I-cyanopindolol binding, was increased by 10 mM MgCl2. The addition of 250 microM GTP reversed this process. In the presence of MgCl2, the competition curves could be resolved into two affinity states of the beta-adrenoreceptor, high and low, respectively. The ratio of the dissociation constant of the high-affinity state to that of the low-affinity state was significantly higher in late-pregnant than in the nonpregnant animals. In the presence of GTP, there was only one (low-affinity) state of the receptor detectable. In both groups of animals, the interaction between beta-adrenoreceptor agonists and myometrial beta-adrenoreceptors was positively modulated by MgCl2. This process was reversed by GTP. However, there appeared to be a differential regulation of the ability of the myometrial beta-adrenoreceptor to form a high-affinity state, depending on the reproductive state of the animal.

Effect of guanosine triphosphate on the release of Ca 2+ from intracellular store sites of saponin-treated human peripheral lymphocytes

The effects of guanosine triphosphate (GTP) on the release and uptake of Ca 2+ in nonmitochondrial intracellular store sites of human peripheral lymphocytes were examined. GTP in the presence of 3% polyethylene glycol released Ca 2+ from the intracellular store sites of lymphocytes in a dose-dependent manner, and the maximal release was obtained at 10 μ m GTP. GDP and 5′-GMP also enhanced the release of Ca 2+. On the other hand, Ca 2+ uptake in the presence of oxalate by saponin-treated lymphocytes was stimulated by GTP and this stimulation was abolished when polyethylene glycol was concomitantly present. The dose dependence of the stimulated Ca 2+ uptake by GTP was much the same as that of the Ca 2+ released by GTP. These results indicate that GTP has an inherent activity to release Ca 2+ as well as to stimulate the uptake of Ca 2+ in nonmitochondrial intracellular store sites of saponin-treated lymphocytes. The stimulatory effect of polyethylene glycol on GTP-mediated Ca 2+ release may occur by inhibiting functions of the Ca 2+ pump.

Is there a connection between high affinity 3H-spiperone binding sites and DA-sensitive adenylate cyclase in corpus striatum ?

The possibility of a connection between the high affinity 3H-spiperone binding sites and the dopamine-sensitive adenylate cyclase system suggested by recent studies was investigated in corpus striatum. When measured under identical conditions (membrane preparation, incubation conditions, presence of dopamine), the affinity of spiperone for its binding site (1.5 × 10 10M) was much higher than its affinity for inhibiting the dopamine sensitive adenylate cyclase (10 7M). Phenoxybenzamine was found to block 3H-spiperone binding irreversibly. Phenoxybenzamine (10 5M) completely supressed 3H-spiperone binding while the adenylate cyclase continued to be stimulated by dopamine (35 per cent of control stimulation) and inhibited by spiperone or haloperidol. The affinities of these neuroleptics for inhibiting the dopamine-sensitive adenylate cyclase were the same on control and phenoxybenzamine treated membranes. Consequently the 3H-spiperone binding site has not to be occupied to allow inhibition of the dopamine-sensitive adenylate cyclase. Guanosine triphosphate reduced the affinities of dopamine, 3-{2-[ N-(3-hydroxyphenylethyl) N-propylamino]ethyl}phenol (RU 24926) and serotonin for 3H-spiperone binding sites and did not affect the affinity of 2-Br-α-ergocriptine. Since RU 24296 and serotonin neither stimulate nor inhibit the dopamine-sensitive adenylate eyclase, the effects of guanosine triphosphate on binding do not appear related to adenylate cyclase activation by agonists which is known to require guanosine triphosphate. Our experiments suggest that the high affnity 3H-spiperone binding sites are not related to the dopamine-sensitive adenylate cyclase.

Stabilization and solubilization of bovine corpus-luteum adenylate cyclase. The effects of guanosine triphosphate, guanosine 5'-[beta,gamma-imido]triphosphate, sodium fluoride and Tris/hydrochloric acid concentration on enzyme activity.

1. Adenylate cyclase of the washed 600g sediment of bovine corpus-luteum homogenate is stimulated by p[NH]ppG (guanosine 5'-[beta,gamma-imido]triphosphate), the imido analogue of GTP, and to a lesser extent by GTP itself. Activation by p[NH]ppG is not reversed by extensive washing before assay, but can, however, be reversed by NaF. 2. Both p[NH]ppG and NaF stabilize the enzyme during incubation at 37 degrees C. NaF also causes an irreversible activation, but only of part of the potentially NaF-activatable adenylate cyclase; there are possibly two components of the adenylate cyclase system, which can be distinguished by their response to NaF. 3. Solubilization of the adenylate cyclase activity in the 600g sediment, by using the non-ionic detergent Lubrol-PX, gave variable yields. A relationship between the magnitude of NaF stimulation of the 600g-sediment enzyme and the yield of soluble activity derived from the sediment was recognized. The results suggest that the pre-existing state of the enzyme complex in vivo is reflected by the response in vitro to NaF and may determine the success with which activity can be solubilized. 4. The absolute yields of soluble activity could be increased by p[NH]ppG preactivation of the 600g sediment. During the development of the maximally active state by preincubation with p[NH]ppG the enzyme passes through a stage in which Lubrol solubilization is increased, but the maximally active state is itself less amenable to solubilization. p[NH]ppG activation causes the appearance of NaF-inhibited states, which appear to be preferentially solubilized by Lubrol-PX.

Adenylate cyclase activity of normal and goitrous rat thyroids.

SummaryThe influence of Mg2+, Mn2+, and Ca2+ as well as the effects of guanosine triphosphate (GTP) and prostaglandin E1 (PGE1) on adenylate cyclase activity in ho-mogenates of thyroid glands from rats treated with propylthiouracil (PTU) and from normal control rats were compared. Increasing concentrations of Mg2+ in the medium stimulated adenylate cyclase activity: at 8 and 12 mM Mg2+, cyclase activity was significantly higher in the PTU-treated group. The effect of Mn2+ on adenylate cyclase activity was essentially the same in goitrous and normal thyroids. Calcium inhibited adenylate cyclase activity; the K1 for Ca2+ (about 0.4 mM) was approximately equal for normal and goitrous glands. There was also no significant difference between goitrous and control thyroid tissue in fluoride-stimulated adenylate cyclase activity determined at various Mg2+ concentrations. Addition of GTP to the assay mixture stimulated adenylate cyclase activity in both groups. GTP also made tissue from both groups of rats respons...

The role of organic phosphates in modulating the oxygenation behavior of eel hemoglobin

Abstract The effects of guanosine triphosphate (GTP) and adenosine triphosphate (ATP) on the oxygen affinity of hemoglobin from the American eel, Anguilla rostrata, were determined. GTP was shown to reduce the oxygen affinity of the pigment to a greater extent than did ATP. The combination of GTP, ATP and NaCl simulating the intraerythrocytic concentrations of salt water and freshwater eels decreased the oxygen affinity more than did either of the individual phosphates suggesting a possible synergistic behavior of the compounds. The interactions between the intraerythrocytic phosphates and ions and ambient salinity are discussed.

The effects of organic phosphates on the oxygenation behavior of eel multiple hemoglobins

1. 1. The effects of guanosine triphosphate (GTP) † † GTP, guanosine triphosphate; ATP, adenosine triphosphate; DPG, 2,3-diphosphoglycerate Hb, hemoglobin. and adenosine triphosphate (ATP) on the oxygenation behavior of the two major hemoglobins of the American eel, Antuilla rostrata, were determined. 2. 2. Both phosphates lower the oxygen affinities of the individual hemoglobins but the effect of GTP is greater than that of ATP. 3. 3. The allosteric effect of these phosphates is more pronounced with HbI than with HbII. 4. 4. Combinations of GTP and ATP at intraerythrocytic ocnentrations lower the oxygen affinities of the pigments to a greater extent than either phosphate alone. 5. 5. Sodium chloride decreases the affinity of HbI but increases the affinity of HbII. 6. 6. The interaction between these phosphates and NaCl in modulating the oxygenation behavior of the multiple hemoglobins of marine and fresh-water eels is discussed.

Immunochemical Studies of Bovine and Frog Liver Glutamate Dehydrogenases

Abstract Rabbit antibody prepared against native bovine liver glutamate dehydrogenase is not a competitive inhibitor of coenzyme at active sites or of nucleotides at modifier (allosteric) sites. The antibody, indeed, activates glutamate dehydrogenase at the active sites of both bovine and frog liver enzymes. At modifier sites the antibody is antagonistic to the effects of purine nucleotides. For example, the antibody partially inhibits the activating effects of adenosine diphosphate and the inhibitory effects of guanosine triphosphate on glutamate dehydrogenase activity. Immunochemical and kinetic experiments indicate that there is a great deal of antigenic similarity between the bovine and frog liver enzymes. These results suggest that the antigenic sites are quite similar in both the bovine and frog enzymes and are not active or allosteric sites. It is possible that antibody is bound to a part of the enzyme molecule which contains neither active nor allosteric sites and which is structurally similar from species to species, while active and allosteric sites differ from species to species.