The stimulus-secretion coupling of amino acid-induced insulin release metabolic interaction L-asparagine and L-leucine in pancreatic islets

1. Because L-asparagine augments insulin release evoked by L-leucine, the metabolism of these two amino acids was investigated in rat pancreatic islets. 2. L-Leucine inhibited the uptake and deamidation of L-asparagine, but failed to exert any obvious primary effect upon the further catabolism of aspartate derived from exogenous asparagine. 3. L-Asparagine augmented the oxidation of L-leucine, and effect possibly attributable to activaion of 2-ketoisocaproate dehydrogenase. 4. The association of L-asparagine and L-leucine exerted a sparing action on the utilization of endogenous amino acids, so that the integrated rate of nutrients oxidation was virtually identical in the sole presence of L-leucine and simultaneous presence of L-asparagine and L-leucine, respectively. 5. It is proposed that the enhancing action of L-asparagine upon insulin release evoked by L-leucine is attributable to an increased generation rate of cytosolic NADPH rather than any increase in nutrients oxidation.     

Infrared spectroscopy of proteins

This review discusses the application of infrared spectroscopy to the study of proteins. The focus is on the mid-infrared spectral region and the study of protein reactions by reaction-induced infrared difference spectroscopy.     

KCNJ8/ABCC9-containing K-ATP channel modulates brain vascular smooth muscle development and neurovascular coupling

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Inhibitory effects of HgCl2 on excitation-secretion coupling at the motor nerve terminal and excitation-contraction coupling in the muscle cell

Summary 1. Indirect and direct twitch (0.1-Hz) stimulation of the rat phrenic nerve-diaphragm disclosed that the inhibitory effect of HgCl₂, 3.7 × 10^–5 M, on the neuromuscular transmission and in the muscle cell, was accelerated by 10-sec periods of 50-Hz tetanic stimulation every 10 min. This activity-dependent enhancement suggested an inhibitory mechanism of HgCl₂ related to the development of fatigue, like membrane depolarization or decreased excitability, decreased availability of transmitter, or interference with the factors controlling excitation-secretion coupling of the nerve terminal, i.e. (Ca²⁺)₀ or (Ca²⁺)_i, and excitation-contraction coupling in the muscle cell, i.e., (Ca²⁺)_i.2. During both indirect and direct stimulation, HgCl₂-induced inhibition was enhanced markedly by pretreatment with caffeine, which releases Ca²⁺ from endoplasmic and sarcoplasmic reticulum in the nerve terminal and muscle cell, respectively. This caffeine-induced enhancement was completely antagonized by dantrolene, which inhibits the caffeine-induced release. However, dantrolene alone did not antagonize the HgCl₂-induced inhibition.3. Since caffeine depletes the intracellular Ca²⁺ stores of the smooth endoplasmic reticulum, HgCl₂ probably inhibits by binding to SH groups of transport proteins conveying the messenger function of (Ca²⁺)_i. In the muscle cell this leads to inhibition of contraction. In the nerve terminal, an additional enhancement of the HgCl₂-induced inhibition, by inhibiting reuptake of choline by TEA and tetanic stimulation, suggested that HgCl₂ inhibited a (Ca²⁺)_i signal necessary for this limiting factor in resynthesis of acetylcholine.4. The (Ca²⁺)₀ signal necessary for stimulus-induced release of acetylcholine was not affected by HgCl₂. Hyperpolarization in K⁺-free solution antagonized the inhibitory effect of HgCl₂ at indirect stimulation, and Ca²⁺-free solution enhanced the inhibitory effect at direct stimulation. K⁺ depolarization, membrane electric field increase with high Ca²⁺, membrane stabilization with lidocaine, and half-threshold stimulation, did not change the inhibitory effect of HgCl CH₃HgCl, 1.85 × 10^–5 M, disclosed a synergistic interaction with caffeine during direct, but not during indirect, stimulation.     

陕西省新型城镇化与生态环境协调度研究

城镇化与生态环境之间相互影响、相互促进，两系统间耦合协调状态对于区域绿色可持续发展意义重大。以陕西省2005—2019年数据为例，在构建新型城镇化与生态环境系统评价指标体系的基础上结合耦合协调度模型、相对发展模型及面板向量自回归(PVAR)模型分析新型城镇化系统与生态环境系统间的耦合协调时空规律及互动关系。结果表明：(1)陕西省耦合协调度总体呈现“基本不协调—基本协调—中度协调”的演变规律。(2)各市耦合协调发展状态空间差异明显，2005年、2013年、2019年陕西省10个城市新型城镇化与生态环境耦合协调发展状态存在较大差异性，相对发展状态整体上由新型城镇化滞后状态发展为生态环境滞后状态。(3)脉冲响应图反映出新型城镇化与生态环境两系统间存在明显互动关系，前期生态环境受新型城镇化冲击的负向抑制作用，后期影响逐渐减小，受自身冲击较大，而新型城镇化发展前后期均主要受自身影响。本研究认为新型城镇化发展必须以生态为优先，在提高生态承载力的基础上，加速提升陕西省各区域空间人口等不同维度城镇化发展水平，从而实现高质量可持续的绿色发展目标。     

Isolated neurosecretory nerve endings as a tool for studying the mechanism of stimulus-secretion coupling

In the present paper we discuss the properties of a recently developed preparation of isolated neurosecretory nerve endings obtained from the rate neurohypophysis. These nerve terminals release two neurohormones, oxytocin and vasopressin, which are easily assayed by radioimmunoassay. Depolarization-induced secretion is dependent on the same parameters as those regulating release from the whole neural lobe. The isolated nerve endings can be permeabilized by means of digitonin; a treatment which gives direct access to the cytoplasm allowing the study of the minimal requirements for inducing neuropeptide release. Furthermore, some nerve endings are large enough to allow the use of the patch-clamp technique. In the present paper we present evidences which show that the isolated neurohypophysial nerve terminals represent a protent tool for studying the mechanism of stimulus-secretion.     

A new gene controlling the frequency of cell division per round of DNA replication in Escherichia coli

Summary A novel mutant of Escherichia coli, named cfcA1, was isolated from a temperature-sensitive dnaB42 strain, and found to have the following characteristics. Division arrest and lethality induced by inhibition of DNA replication was reduced and delayed in the cfcA1 dnaB42 strain, as compared with the parental dnaB42 strain. Two types of inhibition of division induced by the addition of nalidixic acid or hydroxyurea were suppressed by the cfcA1 mutation. Under permissive conditions for DNA replication, the colony forming ability of cfcA1 cells was significantly reduced as compared with that of cfc ⁺ cells; conversely the division rate of cfcA1 cells was higher than that of cfc ⁺ cells. The cfcA1 mutation partially restored division arrest induced in the thermosensitive ftsZ84 mutant at the restrictive temperature and suppresed the UV sensitivity of the lon mutation. The mutation was mapped at 79.2 min on the E. coli chromosome. Taking these properties into account, it is hypothesized that the cfcA gene is involved in determining the frequency of cell division per round of DNA replication by interacting with the FtsZ protein which is essential for cell division.     

Effect of HCO - 3 concentration in the absorption solution on the energetic coupling of H+-cotransports in roots of Zea mays L.

The effect of HCO ₃ ^- on ion absorption by young corn roots was studied in conditions allowing the independent control of both the pH of uptake solution and the CO₂ partial pressure in air bubbled through the solution. The surface pH shift in the vicinity of the outer surface of the plasmalemma induced by active H⁺ excretion was estimated using the initial uptake rate of acetic acid as a pH probe (Sentenac and Grignon (1987) Plant Physiol. 84, 1367). Acetic acid and orthophosphate uptake rates and NO ₃ ^- accumulation were slowed down, while ⁸⁶Rb⁺ uptake and K⁺ accumulation rates were increased by HCO ₃ ^- . These effects were similar to those induced by 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid/2-amino-2-(hydroxymethyl)-1,3-propanediol (Hepes-Tris). They were more pronounced when the H⁺ excretion was strong, were rapidly reversible and were not additive to those of Hepes-Tris. The hypothesis is advanced that the buffering system CO₂/H₂CO₃/HCO ₃ ^- accelerated the diffusion of equivalent H⁺ inside the cell wall towards the medium. This attenuated the surface pH shift in the vicinity the plasma membrane and affected the coupling between the proton pump and cotransport systems.Abbreviations FW fresh weight - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - J_aa acetic acid influx - J_K ⁺ K⁺ influx - J_Pi orthophosphate influx - Mes 2-(N-morpholino)ethanesulfonic acid - pCO₂ CO₂ partial pressure - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

A review of the in vitro and in vivo neurochemical characterization of the NMDA/PCP/Glycine/Ion channel receptor macrocomplex

Conclusions Current neurochemical studies of the NMDA receptor macromolecular complex are yielding new insights into the interactions of the subunits of this complex and the associated potential clinical benefits of selective modulation of these subnits. Such studies offer the great potential for a new generation of pharmacotherapies for a wide range of CNS disorders, including stroke, a condition for which there is currently no effective pharmacological treatment. However, it is essential to understand that the first generation products in this area may not be optimal pharmacotherapies, such that haracterization of possible receptor subtypes and understanding the molecular biology of the component proteins of the receptor complex will be crucial in the design of the optimal pharmacological modulators of the NMDA receptor complex.Special issue dedicated to Dr. Erminio Costa     

Multisegmental cobalt filling of the dorsal giant fibers in the nervous system of the earthworm,Lumbricus terrestris

Summary The anatomical organization of the two dorsal giant fiber systems of the earthworm Lumbricus terrestris is demonstrated in whole mounts and serial-section reconstructions based on backfillings of the ventral nerve cord with cobalt chloride. Both the medial and lateral fiber systems can be labeled selectively over more than ten body segments. They show a characteristic segmental pattern of collaterals with some modification in tail segments and of dorsal plasma protrusions in the unpaired medial giant fiber presumably representing openings in the myelin sheath. We found no multisegmental cobalt transport in other large neurons of the nerve cord. Cobalt passes through the segmentai septa between consecutive axonal elements of the metameric giant fibers and presumably also through commissural contacts between specific collaterals of the lateral giant fibers. Since these sites of contact are known to represent electrical synapses, cobalt coupling may, in L. terrestris, correlate with functional electrotonic coupling.Abbreviations CL collateral of lateral giant fiber - CM collateral of medial giant fiber - GIN giant interneuron - LGF lateral giant fiber - MGF medial giant fiber - SN segmental nerve