Investigation of function of the lactose operon of escherichia coli K-12 under the influence of nonspecific regulators

The possible role of cyclic AMP in the stimulating action of ACTH and hydrocortisone on the lactose operon ofEscherichia coli K-12 was investigated. It was shown that ACTH had no effect on strainsE. coli WZ-78/F'lac (cya₈₅₅) andE. coli CA 8001 (L₁), in which the system of regulation of the function of the lactose operon by cyclic AMP is disturbed. Meanwhile this hormone stimulates the lactose operon in wild-type strains:E. coli 200 PS/F'lac andE. coli 3000. Hydrocortisone stimulates the function of the lactose operon both in the wild-type strainE. coli 3000 and in the mutantE. coli CA 8001 (L₁). It is considered that the stimulating action of ACTH on the lactose operon is mediated through cyclic AMP and that hydrocortisone stimulates the function of the lactose operon independently of cyclic AMP.Research Laboratory of Experimental Immunobiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR N. N. Zhukov-Verezhnikov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 33, No. 6, pp. 744–746, June, 1977.     

Cellular and membrane events involved in the K-induced increase in water permeability of toad skin

Exposure of the inner surface of toad skin (Bufo marinus) to high [K⁺] resulted in a marked (up to 7-fold) increase in water permeability (P _f) that was more marked in KCl-Ringer than in K₂SO₄-Ringer. Although high [K⁺] did not clicit a maximal increase inP _f, it blunted the hydrosmotic responses to vasopressin, isoproterenol and cAMP. Both post-cAMP inhibitors of stimulated water flow, such as diamide and vanadate, and pre-cAMP inhibitors, such as methohexital and propranolol, markedly reduced the K response, while exposure to Ca²⁺-free, KCl-Ringer did not inhibit water flow. Intramembrane particle aggregates, similar to those induced by cAMP-mediated hydrosmotic agents, were seen in the apical membrane of granular cells, just beneath thestratum corneum, in skins exposed to KCl. Available evidence indicates that cAMP might mediate, at least partially, the hydrosmotic effect of high [K⁺]. In contrast, a role of voltage-dependent Ca²⁺ channels, described in other cell systems depolarized with K, was not apparent in toad skin.     

Cytochemical localization of 5'-nucleotidase activity in retinal photoreceptor cells

Further cytochemical studies on the ultrastructural localization of 5'-nucleotidase in the rat retina have revealed activity to be associated with the complex synapses formed by the rod spherules of the receptors and the bipolar and horizontal cell processes. Activity was also seen on the axolemma of receptor fibers. In the rod inner segment strong reaction product is located intracellularly. In the rod outer segment the enzyme appears to be located only on the cytoplasmic side of the disc membrane and not intradiscally . Retinal pigment cells are rich in 5'-nucleotidase. Their microvilli accompany the tips of the receptor cells and show enzyme activity in an ecto position. A role for 5'-nucleotidase is possible in the metabolism of guanylate and adenylate nucleotides both of which are important for visual transduction processes.     

Involvement of GPR12 in the induction of neurite outgrowth in PC12 cells

GPR12, an orphan G protein-coupled receptor, constitutively activates the Gs signaling pathway and further increases intracellular cyclic AMP. GPR12 overexpression has been reported to promote neurite extension in neurons or transform neuro2a neuroblastoma cells into neuron-like cells. However, the possible effects and mechanisms of GPR12 in the differentiation of PC12 cells are still unknown. The present study shows that GPR12 overexpression induced PC12 cells differentiation into neuron-like cells with enlarged cell sizes and neuritogenesis possibly via activation of Erk1/2 signaling and significantly increased the expression of several neurite outgrowth-related genes, including Bcl-xL, Bcl-2 and synaptophysin. These findings indicate that GPR12 may play a role in neurite outgrowth during PC12 cell differentiation.     

Effects of dopamine on cyclic AMP concentration in the anterior pituitary glandin vitro

Summary Effects of different concentrations of dopamine on the cyclic AMP concentration in the rat anterior pituitary gland were investigated in vitro. Low concentrations of dopamine (10^–9–10^–8 mol/l) were found to decrease, whereas the high concentration (10^–5 mol/l) increased the cyclic AMP concentration in pituitaries collected from ovariectomized and estradiol-treated females. In contrast, dopamine had no effect on the anterior pituitary cAMP concentration when pituitaries were collected from ovariectomized rats which had not received estrogen replacement. These data show that the action of dopamine on the anterior pituitary cAMP largely depends on the dopamine concentration and the hormonal state of animals.This paper was supported by the Polish Academy of Sciences Grant No. 10.4.2.01.5.5.     

Effects of dibutyryl cyclic AMP and forskolin on phospholipid biosynthesis in thrombin-stimulated human platelets

The influence of forskolin, an adenylate cyclase activator, and of dibutyryl cyclic AMP (Bt2cAMP) on [3H]glycerol incorporation into glycerolipids was investigated in human platelets. It was found that preincubation with 2.5 mM Bt2cAMP produced a 2-4-fold increase in thrombin-induced incorporation into phospholipids compared to platelets activated by thrombin alone. Pretreatment with forskolin, which increased cellular cAMP content, also resulted in an increase in thrombin-stimulated [3H]glycerol incorporation into phospholipids. These findings demonstrate that a rise in platelet cAMP can accentuate thrombin-induced de novo synthesis of phospholipids from [3H]glycerol. Since the content of cellular cAMP was correlated with its ability to inhibit platelet activation monitored by serotonin release, it seems likely that glycerolipid, in particular phospholipid biosynthesis, is involved in controlling platelet activation by thrombin.     

Antipsychotics with inverse agonist activity at the dopamine D3 receptor

Summary In NG 108-15 cells expressing the recombinant human D₃ receptor, dopamine agonists enhance [³H]thymidine incorporation and decrease cAMP accumulation. In these cells, but not in wild type cells, haloperidol, fluphenazine, and various other antipsychotics inhibited basal [³H]thymidine incorporation in a concentration-dependent manner. In contrast, other dopamine antagonists such as nafadotride or (+)AJ 76, two D₃-preferring antagonists, were without effect. The concentration-response curve of haloperidol was shifted to the right in presence of nafadotride, with a potency compatible with its nanomolar apparent affinity as neutral antagonist. Pertussis toxin treatment abolished or markedly reduced the responses to haloperidol or fluphenazine. In contrast, no significant enhancement of cAMP accumulation could be observed, under the influence of haloperidol or eticlopride. These data indicate that some dopamine antagonists behave as inverse agonists, and thus appear to inhibit an agonist-independent activity of the D₃ receptor on [³H]thymidine incorporation pathway, but not on the cAMP pathway.     

Axonal transport of adenylate cyclase activity in normal and axotomized frog sciatic nerve

Adenylate cyclase activity accumulated proximal to a constriction placed around the frog sciatic nerve. The rate of accumulation was linear between 8 and 24 h following placement of the constriction; accumulation rate declined substantially after 24 h. Accumulation of activity distal to the constriction in normal nerve was not significantly different from control for the first 72 h, but increased at 5 days. These data are interpreted as indicating that adenylate cyclase is transported from the cell body to the nerve terminals in normal frog nerve, but not in the reverse direction. Following axon transection, anterograde transport of adenylate cyclase activity declined, but a transient retrograde transport of adenylate cyclase activity appeared. In addition, adenylate cyclase activity accumulated in the proximal transected nerve stump during the period when Schwann cell proliferation and the initiation of nerve regeneration both appear. The pattern of response of adenylate cyclase activity to nerve injury suggests that the adenylate cyclase: cAMP system could play some role in peripheral nerve regeneration.     

纳络酮对缺血再灌注心肌腺苷酸环化酶活性和环磷酸腺苷含量的影响

利用犬心肌缺血再灌注模型观察纳络酮对缺血再灌注心肌腺苷酸环化酶（ＡＣ）活性和环磷酸腺苷（ｃＡＭＰ）含量的影响以及纳络酮在体外对心肌ＡＣ活性的影响。结果表明：心肌缺血和缺血再灌注后，ＡＣ活性及ｃＡＭＰ含量均明显增高（Ｐ＜０．０５，Ｐ＜０．０１），缺血心肌ＡＣ活性明显高于再灌注心肌（Ｐ＜０．０５）；静脉注射纳络酮能明显降低缺血再灌注心肌ＡＣ活性和ｃＡＭＰ含量（Ｐ＜０．０５，Ｐ＜０．０１），但对生理盐水治疗的动物正常（模拟手术）、缺血和再灌注心肌匀浆ＡＣ活性无明显作用（Ｐ＞０．０５）。提示，纳络酮本身对ＡＣ活性无抑制作用，其降低缺血再灌注心肌ｃＡＭＰ含量可能涉及酶前因素。