High affinity uptake of L-glutamate and γ-aminobutyric acid inDrosophila melanogaster

Preparations having properties resembling those of synaptosomes have been isolated from whole fly homogenates ofDrosophila melanogaster using ficoll gradient floatation technique. These have been characterized by marker enzymes and electron microscopy and binding of muscarinic antagenist³H Quinuclidinyl benzilate. An uptake system for neurotransmitter, ã-Aminobutyric acid has been demonstrated in these preparations. A high affinity uptake system for L-glutamate has also been studied in these subcellular fractions. This uptake of glutamate is transport into an osmotically sensitive compartment and not due to binding of glutamate to membrane components. The transport of glutamate has an obligatory requirements for either sodium or potassium ions. Kinetic experiments show that two transport systems, withK _m values 0.33 X 10^-6M and 2.0 X 10^-6M, respectively, function in the accumulation of glutamate. ATP stimulates lower affinity transport of glutamate. Inhibition of glutamate uptake by L-aspartate but not by phenylalanine and tyrosine indicates that a common carrier mediates the transport of both glutamate and aspartate. β-N-oxalyl-L-β β-diamino propionic acid and kainic acid, both inhibitors of glutamate transport in mammalian brain preparations, strongly inhibited transport of glutamate inDrosophila preparations Comparison with uptake of ã-aminobutyric acid and glutamate in isolated larval brain is presented to show that the synaptosome-like preparations we have isolated are rich in central nervous system derived structures, and presynaptic endings from neuromuscular junctions.     

Effect of rainstorms on heterotrophic bacterial activity in a hypertrophic African lake

Hartbeespoort Dam is a hypertrophic man-made lake which is located in the Transvaal Province of South Africa. This region has recently experienced its most severe drought of the century. However, on three occasions in the summer rainy seasons of 1984 and 1985, major rainfalls (> 50 mm) occurred which caused large inflows to the lake. Inflowing river water entered as a density current causing marked silting of the water. Within the epilimnion (0–10 m) prior to these rainfalls there was usually no variation of bacterial numbers with depth, but heterotrophic bacterial activity (glucose uptake) decreased with depth concomitant with primary production. With the increased river inflow bacterial numbers did not increase but bacterial activity at the bottom of the epilimnion (10 m) increased to as high as 2.7 µg C l^–1 h^–1 in January 1985, reversing the depth profile of bacterial activity within the epilimnion. This resulted in decreased glucose concentrations (K_t + S_n) and turnover times. Heterotrophic activity per cell increased by between 2.5 and 5 times. These data demonstrate that storm events are important phenomena causing short-term changes in the metabolic activity of planktonic heterotrophic bacteria in lakes.     

Temperature Dependence of Drug Interaction with the Platelet 5-Hydroxytryptamine Transporter: A Clue to the Imipramine Selectivity Paradox

Although [3H]imipramine is a selective radioligand for the 5-hydroxytryptamine (5-HT) transporter in human platelets, its affinity for binding to the 5-HT transporter complex at 0 degrees C (0.6 nM) is significantly higher than its potency for inhibition of [3H]5-HT uptake at the physiological temperature of 37 degrees C (Ki = 29 nM). As this apparent discrepancy could be related to the assay temperature, we studied the thermodynamics of drug interaction with the 5-HT transporter at assay temperatures between 0 degrees C and 37 degrees C, using as radioligands [3H]imipramine (0 degrees C and 20 degrees C) and [3H]paroxetine (20 degrees C and 37 degrees C), a newly available probe for the 5-HT transporter. At 20 degrees C, Ki values of 14 tricyclic and nontricyclic drugs for inhibition of [3H]imipramine and [3H]paroxetine binding to human platelet membranes were highly significantly correlated (r = 0.98, p less than 0.001), validating the use of these two radioligands to study the 5-HT transporter over a temperature range larger than was previously possible with [3H]imipramine alone. The affinity of imipramine for the 5-HT transporter is progressively enhanced with decreasing incubation temperature, thus favoring the selectivity of [3H]imipramine for the 5-HT transporter at 0 degrees C. At 37 degrees C, the Ki of imipramine for inhibition of [3H]paroxetine binding is 32 nM, and equals its Ki value for inhibition of 5-HT uptake into human platelets. With the exception of chlorimipramine, other tricyclic 5-HT uptake inhibitors showed a temperature sensitivity in their interaction with the 5-HT transporter similar to that of imipramine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of Exogenous Gangliosides on Amino Acid Uptake and Na+,K+-ATPase Activity in Superior Cervical and Nodose Ganglia of Rats

The effects of some gangliosides on active uptake of nonmetabolizable alpha-aminoisobutyric acid (AIB) and Na+, K+-ATPase and Ca2+, Mg2+-ATPase activities in superior cervical ganglia (SCG) and nodose ganglia (NG) excised from adult rats were examined during aerobic incubation at 37 degrees C for 2 h. In NG, amino acid uptake was greatly accelerated with the addition of galactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylgluc osyl ceramide (GM1) (85%) and also with N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosyl ceramide (GM2) or [N-acetylneuraminyl]-galactosyl-N-acetylgalactosaminyl-[N-acetyl- neuraminyl]-galactosylglucosyl ceramide (GD1a) (43% each) compared with a nonaddition control at a 5 nM concentration. Under identical conditions, Na+, K+-ATPase activity was strongly stimulated with GM1 (180%) and GD1a (93%), whereas Ca2+, Mg2+-ATPase activity showed no change. In SCG, on the other hand, AIB uptake was apparently inhibited (-27%) by addition of GM1, with a slight decrease in Na+, K+-ATPase but no change in Ca2+, Mg2+-ATPase activity in the tissue. Both asialo-GM1, in which N-acetylneuraminic acid is deficient, and Forssman glycolipid, which is not present in nervous tissue, failed to produce any significant increase in both SCG and NG not only in amino acid uptake, but also in Na+, K+-ATPase activity. A kinetic study of active AIB uptake showed that GM1 ganglioside produced an increase in Km with no change in Vmax in SCG, whereas it caused a decrease in Km with a slight increase in Vmax in NG. Treatment of NG and SCG with neuraminidase from Vibrio cholerae, an enzyme that split off sialic acid from polysialoganglioside, leaving GM1 intact, caused little inhibition of the amino acid uptake.(ABSTRACT TRUNCATED AT 250 WORDS)     

[3H]Dipyridamole Binding to Guinea Pig Brain Membranes: Possible Heterogeneity of Central Adenosine Uptake Sites

The binding of [3H]dipyridamole ([3H]DPR) to guinea pig brain membranes is described and compared to that of [3H]nitrobenzylthioinosine ([3H]NBI). The binding of [3H]DPR is saturable, reversible, and specific with pharmacologic evidence indicating that this ligand is binding to the adenosine uptake site. Compared to [3H]NBI the binding of [3H]DPR is of higher capacity (Bmax = 208 +/- 16 fmol/mg protein for [3H]NBI and 530 +/- 40 fmol/mg protein for [3H]DPR) and lower affinity (KD = 0.35 +/- 0.02 nM for [3H]NBI and 7.6 +/- 0.7 nM for [3H]DPR). The adenosine uptake inhibitors are the most potent inhibitors of binding (Ki of 10(-8)-10(-7) M) whereas adenosine receptor ligands such as cyclohexyladenosine, 2-chloroadenosine, and various methylxanthines are several orders of magnitude less potent (Ki 10(-5)-10(-2). The inhibition of [3H]DPR binding by NBI is biphasic, with only 40% of binding being susceptible to inhibition of NBI concentrations less than 10(-5) M. The tissue distribution of [3H]DPR binding parallels that of [3H]NBI although in most cases significantly more sites are observed with [3H]DPR. Calcium channel blocking agents such as nifedipine, nimodipine, and verapamil are also inhibitors of [3H]DPR binding with potencies in the micromolar range. The data are consistent with [3H]DPR being a useful additional ligand for the adenosine uptake site and provide evidence that multiple uptake binding sites exist of which only about 40% are NBI-sensitive.     

Effect of Quinolinic Acid in the Nucleus Basalis Magnocellularis on Cortical High-Affinity Choline Uptake

A transient 45% increase in cortical high-affinity choline uptake (HACU) was observed after an injection of quinolinic acid (QUIN) into the nucleus basalis magnocellularis (nbM) of the rat. This was followed by a steady decline in choline uptake, which resulted in a 46% decrease by day 7. Specific [3H]hemicholinium-3 binding to coronal brain sections showed a similar pattern following injections of QUIN into the nbM. The increase in cortical HACU elicited by QUIN appeared to be dose dependent.     

Low-Level Microwave Irradiations Affect Central Cholinergic Activity in the Rat

Sodium-dependent high-affinity choline uptake was measured in various regions of the brains of rats irradiated for 45 min with either pulsed or continuous-wave low-level microwaves (2,450 MHz; power density, 1 mW/cm2; average whole-body specific absorption rate, 0.6 W/kg). Pulsed microwave irradiation (2-microseconds pulses, 500 pulses/s) decreased choline uptake in the hippocampus and frontal cortex but had no significant effect on the hypothalamus, striatum, and inferior colliculus. Pretreatment with a narcotic antagonist (naloxone or naltrexone; 1 mg/kg i.p.) blocked the effect of pulsed microwaves on hippocampal choline uptake but did not significantly alter the effect on the frontal cortex. Irradiation with continuous-wave microwaves did not significantly affect choline uptake in the hippocampus, striatum, and hypothalamus but decreased the uptake in the frontal cortex. The effect on the frontal cortex was not altered by pretreatment with narcotic antagonist. These data suggest that exposure to low-level pulsed or continuous-wave microwaves leads to changes in cholinergic functions in the brain.     

Stimulation of phospholipase D activity and indication of acetylcholine synthesis by oleate in rat brain synaptosomal preparations

It had been previously demonstrated that the oleate activation of synaptosomal membrane phospholipase D liberated choline which was available for acetylcholine formation. The present investigations were undertaken to determine if oleate might have an effect on choline uptake by synaptosomes. It was observed that oleate interfered with choline uptake when incubations were carried out at 37°C but uptake was stimulated at 3°C. Oleate was the most effective fatty acid of several tested. Preliminary observations suggest the presence of a membranous form of choline acetyltransferase.     

Responses of wild plants to nitrate availability

Summary Two annual species of Bromus, an invader (B. hordeaceus, ex B. mollis) and a non-invader (B. intermedius), were grown for 28 days in growth chambers, at 5 and 100 M NO ₃ ^- in flowing nutrient solution. No differences between the two species were observed at either NO ₃ ^- level, in terms of relative growth rate (RGR) or its components, dry matter partitioning, specific NO ₃ ^- absorption rate, nitrogen concentration, and other characteristics of NO ₃ ^- uptake and photosynthesis. The effects of decreasing NO ₃ ^- concentration in the solution were mainly to decrease the NO ₃ ^- concentration in the plants through decreased absorption rate, and to decrease the leaf area ratio through increased specific leaf mass and decreased leaf mass ratio. Organic nitrogen concentration varied little between the two treatments, which may be the reason why photosynthetic rates were not altered. Consequently, RGR was only slightly decreased in the 5-M treatment compared to the 100-M treatment. This is in contrast with other species, where growth is reduced at much higher NO ₃ ^- concentrations. These discrepancies may be related to differences in RGR, since a log-linear relationship was found between RGR and the NO ₃ ^- concentration at which growth is first reduced. In addition, a strong linear relationship was found between the RGR of these species and their maximum absorption rate for nitrate, suggesting that the growth of species with low maximum RGR may be partly regulated by nutrient uptake.     

Interaction between nitrogen and photon flux density in birch seedlings at steady-state nutrition

Birch ( Betula pendula Roth.) was investigated under steady-state nutrition and growth at different incident photon flux densities (PFD) and different relative addition rates of nitrogen. PFD had a strong influence on the relative growth rate at optimum nutrition and on the nitrogen productivity (growth rate per unit of nitrogen) but little effect on the formal relationships between nitrogen and growth, i.e. PFD and nitrogen nutrition are orthogonal growth factors. At a given suboptimum nitrogen (the same distance from optimum), increased PFD increased the relative growth rate and, therefore, the relative uptake rate and the required relative addition rate in accordance with the theoretical equality between these three parameters at steady-state nutrition. Correspondingly, at a given suboptimum relative addition rate, increased PFD decreased nitrogen status (larger distance from optimum) at an unchanged relative growth rate. Nutrient uptake rate, dry matter content, and partitioning of biomass and nutrients are strongly influenced by nitrogen status. PFD influences these characteristics, but only to an extent corresponding to its effect on the nitrogen status. The influence of PDF on the relative growth rate at optimum and on nitrogen productivity is well described by hyperbolic relationships, similar to reported PFD/photosynthesis relationships. These expressions for plant growth as well as the productivities of leaf area and quantum appear to be valuable characteristics of plant responses to light and nutrition. Although the calculated PFD/growth relationships indicate saturation at high values of PFD, a more realistic estimate of PFD at which saturation occurs is about 30 mol m⁻² day⁻¹, where the highest relative growth rate and nitrogen productivity were experimentally determined. No significant effect was observed because of day length differences between the present and previous experiments.