Tonic GABAergic inhibition of taste-responsive neurons in the nucleus of the solitary tract

The effects of gamma-aminobutyric acid (GABA) and the GABAA receptor antagonist bicuculline methiodide (BICM) on the activity of taste- responsive neurons in the nucleus of the solitary tract (NST) were examined electrophysiologically in urethane-anesthetized hamsters. Single neurons in the NST were recorded extracellularly and drugs (21 nl) were microinjected into the vicinity of the cell via a multibarrel pipette. The response of each cell was recorded to lingual stimulation with 0.032 M NaCl, 0.032 M sucrose, 0.0032 M citric acid and 0.032 M quinine hydrochloride (QHCl). Forty-six neurons were tested for the effects of GABA; the activity of 29 cells (63%) was inhibited by 5 mM GABA. Whether activity was elicited in these cells by repetitive anodal current stimulation (25 microA, 0.5 s, 0.1 Hz) of the tongue (n = 13 cells) or the cells were spontaneously active (n = 13 cells), GABA produced a dose-dependent (1, 2 and 5 mM) decrement in activity. Forty- seven NST neurons were tested for the effects of BICM on their responses to chemical stimulation of the tongue; the responses of 28 cells (60%) were enhanced by 10 mM BICM. The gustatory responses of 26 of these cells were tested with three concentrations (0.2, 2 and 10 mM) of BICM, which produced a dose-dependent increase in both spontaneous activity and taste-evoked responses. Nine of these neurons were sucrose- best, seven were NaCl-best, eight were acid-best and two responded best to QHCl. The responses to all four tastants were enhanced, with no difference among neuron types. For 18 cells that were tested with two or more gustatory stimuli, BICM increased their breadth of responsiveness to their two most effective stimuli. These data show that approximately 60% of the taste-responsive neurons in the rostral NST are inhibited by GABA and/or subject to a tonic inhibitory influence, which is mediated by GABAA receptors. The modulation of these cells by GABA provides a mechanism by which the breadth of tuning of the cell can be sharpened. Modulation of gustatory activity following a number of physiological changes could be mediated by such a GABAergic circuit.      

The microbial synthesis of flavin nucleotides: A review

Recent data on the synthesis and hydrolysis of flavin nucleotides in yeast and bacteria and the regulation of this process are summarized. Specific examples are provided and the prospects of the use of genetically modified microorganisms for the industrial manufacturing of flavin mononucleotide and flavin adenine dinucleotide are considered.     

Bioremediation of chromium by the yeast Pichia guilliermondii: toxicity and accumulation of Cr (III) and Cr (VI) and the influence of riboflavin on Cr tolerance

A comparative study has been made on the sensitivity of the yeast Pichia guilliermondii to Cr (III) and Cr (VI) as well as on the Cr uptake potential at growth-inhibitory concentrations of chromium. The strains used in the study were either isolated from natural sources or obtained from a laboratory strain collection. The results show that most of the natural strains were more tolerant to chromium and were able to grow in the presence of 5 mM Cr (III) or 0.5 mM Cr (VI), that is at concentrations which substantially inhibited the growth of laboratory strains. The cellular Cr content after treatment was similar for both strain types and ranged from 1.2-4.0 mg/g d.w. and 0.4-0.9 mg/g d.w., for Cr (III) and Cr (VI) forms, respectively, however, in one case of a natural strain it reached the value of 10 mg Cr (III)/g dry mass. Natural-source strains were grouped into four groups based on the yeasts' differential response to Cr (III) and Cr (VI). Hexavalent Cr-resistant mutants of a P. giuilliermondii laboratory strain, which revealed markedly changed capabilities of chromium accumulation, were obtained by means of UV-induced mutagenesis. Cr (VI) treatment triggered oversynthesis of riboflavin and the addition of exogenous riboflavin increased P. guilliermondii resistance to both Cr (III) and Cr (VI). Electrophoretic protein profiles revealed the induction and/or suppression of several proteins in response to toxic Cr (VI) levels.     

Secretion and degradation of parathormone as a function of intracellular maturation of hormone pools

The biosynthesis, processing, and secretion of parthormone and the effect of calcium on these processes were measured in dispersed porcine parthyroid cells incubated with [(35)S]methionine. Proparathormone was detected at 10 min, the earliest time measured, and was rapidly and apparently quantitatively converted to parathormone. The half-life of the prohomormone pool was 15 min. Secretion of parathormone was detected by 20 min. In pulse-chase experiments there was a period between 20 and 40 min during which the wave of newly-synthesized parathormone was secreted. After 40 min during little additional radioactive hormone was secreted, but dibutyryl cyclic AMP, an agent that can mobilize stored parathormone, when added to the incubation mixtures enhanced radioactive parathormone secretion but only after 60 min, although it increased net hormone secretion as determined by radioimmunoassay to the same extent at all times studied. When the ionized calcium concentration of the medium was lowered, more radioactive hormone was secreted at all times but the effect was greatest on that hormone that was synthesized less than 60 min previously ; however, net hormone secretion in contrast to radioactive hormone was enhanced equally at all intervals. These data could mean that the refractoriness to secretion of parathormone 40-60 min of age was related to maturation of secretory container preparatory to storage. Low calcium (0.5 mM) stimulated hormone secretion up to fivefold compared to high calcium (3.0 mM) but did not affect synthesis of parathormone or proparathormne or conversion of the latter to hormone. During processing at least 70 percent of the intracellular parathormone was lost, presumably through proteolysis and this degradation was greater at high calcium. These data have been interpreted in light of the concept that two secretable pools of parathormone exist within the parathyroid.     

Nitrite reductase activity of deoxyhemoglobin in diabetes and its correction by nicotinamide

The increase of deoxyhemoglobin nitrite-reductase activity was established at streptozotocin-induced diabetes in rats. The deoxyhemoglobin nitrosilation in the streptozotocin-induced diabetic rats was shown to increase the optical density in the aromatic acid region and cause additional absorption peak at 334 nm. The two-week injection of nicotinamide causes reduction in the nitrite reductase activity of the deoxyhemoglobin and the absorption peak at 334 nm disappearance.     

Spectral properties of myoglobins from aquatic mammals

Spectral characteristics of ferri- and ferroderivatives of myoglobins have been studied in semiwater mammals. Extinction coefficients in the visible range of the spectrum have been determined for different derivatives of the studied heme proteins. It is established that variations in the maxima and minima of different absorption bands are inconsiderable. Close positions of isobestic points have been revealed for a system of oxyglobin and reduced myoglobin obtained from the muscles of the studied animals. Changes in spectral characteristics of methmyoglobins, induced by the effect of different pH, are identical, which evidences for similarity of the surroundings of active site of the studied heme proteins.     

Effect of carnosine on the transformation of sodium nitrite in vitro in the presence of catalase]

It was shown that carnosine changes the compacting of ferment's globe. On the one hand, that action is causes with the connecting of haem. On the other hand, carnosine influences on the hydrate's membrane around protein. Dipeptide influences also on the interaction of catalase with sodium nitrite, which intensity depends on sequence of introducing HNO2 and carnosine into the medium.