Recovery of acetylcholinesterase activity after irreversible inhibition by organophosphorous compounds in embryonic development

1. Recovery of acetylcholinesterase (AChE) activity was studied using the embryos of sea urchins Strongylocentrotus intermedius and S. nudus, embryos of axolotl Ambystoma mexicanum and in the chick embryo muscle culture treated by "irreversible" organophosphorous inhibitors (OPI). 2. AChE activity was assayed by a modified Ellman's procedure. 3. It follows from the data obtained that, unlike the plutei of sea urchins and the monolayer culture of chick embryo muscle cells, the embryos of axolotl show a compensatory increase in AChE biosynthesis after inhibition by OPI. 4. This mechanism is assumed to be related to the presence of a well developed neuromuscular system in the A. mexicanum embryos. 5. It is possible that acetylcholine accumulated as a result of partial AChE inhibition is responsible for the compensatory increase in AChE biosynthesis.     

Study of 2'-phosphodiesterase activity in cultured NIH 3T3 cells during activation of cAMP-dependent phosphorylation

A rapid and transient decrease in 2'-phosphodiesterase activity in NIH 3T3 mouse cells was observed after adrenaline addition. The decrease of activity was accompanied by an elevation of intracellular cAMP level. The 2'-phosphodiesterase activity changed similarly when cells sink deeper into the resting state. In the latter case, the fall of the enzyme activity was correlated with elevation of the activity of cAMP-dependent proteinkinase and, moreover, a considerable increase of the intracellular level of 2',5'-oligoadenylate was observed. Phosphorylation of proteins by cAMP-dependent proteinkinase in the cell lysate also produced a pronounced drop of 2'-phosphodiesterase activity. Exogenous 2',5'-oligo (A) treatment of the cells resulted in the rise of 2'-phosphodiesterase activity; actinomycin D prevented this effect. The data presented suggest the involvement of two different mechanisms in regulation of 2'-phosphodiesterase activity: cAMP-dependent phosphorylation and induction of 2'-phosphodiesterase by 2',5'-oligoadenylate.     

Change inLimnaea stagnalis neuronal response to acetylcholine during intracellular and extracellular perfusion with serotonin

The modifying effect of adding serotonin to the intra- and extracellular environment on the inward currents generated by the cell following intracellular application of acetylcholine was shown during studies on unidentified isolatedLimnaea stagnalis neurons using techniques of intracellular perfusion and voltage clamping. Serotonin inhibited response to achetylcholine in both cases in most of the test neurons. Serotonin intensified this response when applied to the intracellular environment and produced the opposite effect of reducing the amplitude of inward acetylcholine currents when administered extracellularly. Cyproheptadine, the serotonin receptor blocker, inhibited the enhancing effect of serotonin produced by adding this neurotransmitter to the intracellular fluid, but mimicked the inhibitory effects of serotonin on response to acetylcholine, whether added to the intra- or extracellular environment. Findings would suggest the presence of intracellular serotonin receptors in the mollusk neurons; one of their possible functions could be controlling the sensitivity of the cell surface cholinoreceptors.N. K. Koltsov Institute of Developmental Biology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 326–332, May–June, 1986.     

Cyclic AMP-dependent regulation of activities of synthetase and phosphodiesterase of 2′,5′-oligoadenylate in NIH 3T3 cells

Summary Dihydrofolate synthetase (EC 6.3.2.12) from N. gonorrhoeae was isolated and enzyme characteristics were determined. The purified enzyme was found quite stable when stored at –60 °C. About 50% of the enzyme activity wag destroyed within 6 weeks when kept at 4 °C. Maximum velocity was observed at pH 9.3. The enzyme required a monovalent cation, K⁺ or NH₄ ⁺ , and divalent cation, Mg²⁺ or Mn²⁺ for its function. ATP at 5 mM concentration gave maximum activity. K_m values for dihydropteroate and L-glutamate at pH 9.3 were 3.5 × 10^–5 M and 6.5 × 10^–4 M, respectively. Patterns of product inhibition by dihydrofolate were found to be non-competitive with respect to dihydropteroate, having a K_i value of 5.1 ± 0.8 × 10^–4 M, and competitive with respect to L-glutamate, having a K_i value of 6.2 × 10^–4 M.     

Glucagon signalling in the dorsal vagal complex is sufficient and necessary for high‐protein feeding to regulate glucose homeostasis in vivo

High‐protein feeding acutely lowers postprandial glucose concentration compared to low‐protein feeding, despite a dichotomous rise of circulating glucagon levels. The physiological role of this glucagon rise has been largely overlooked. We here first report that glucagon signalling in the dorsal vagal complex (DVC) of the brain is sufficient to lower glucose production by activating a Gcgr–PKA–ERK–K_ATP channel signalling cascade in the DVC of rats in vivo. We further demonstrate that direct blockade of DVC Gcgr signalling negates the acute ability of high‐ vs. low‐protein feeding to reduce plasma glucose concentration, indicating that the elevated circulating glucagon during high‐protein feeding acts in the brain to lower plasma glucose levels. These data revise the physiological role of glucagon and argue that brain glucagon signalling contributes to glucose homeostasis during dietary protein intake.     

Patterns in the binding of cytotoxic neuropharmacologic preparations by early sea urchin embryos]

Early embryos of Arbacia lixula, Paracentrotus lividus and Sphaerechinus granularis intensively bind cytotoxic neuropharmacological drugs, such as antiserotonine indole derivatives, cholinolytics and tricyclic antidepressants. The binding intensity decreases markedly upon quaternization of the drugs. Quantitative analysis indicates that: a)with respect to the drugs, the suspension of living embryos may be described as a single adsorbing system following the Langmuir equation; b) at least two independent binding pools exist in embryos; c) the magnitude of cytotoxic effect of a given drug is not proportional to its binding.