Inhibitory innervation of a lobster muscle

Summary Inhibitory neuromuscular synapses formed by the common inhibitor (CI) neuron on the distal accessory flexor muscle (DAFM) in the lobster, Homarus americanus, were studied with electrophysiological and electron-microscopic (thin-section and freeze-fracture) techniques. Postsynaptic inhibition as indicated by inhibitory junctional potentials was several-fold stronger on distal compared to proximal muscle fibers. This difference correlated with the results of serial thin-section studies, which showed more inhibitory synapses on distal fibers than on their proximal counterparts. Effects of postsynaptic inhibition on excitatory junctional potentials via current shunting had a morphological correlate in the spatial relationship between inhibitory and excitatory synapses on the distal fibers. Inhibitory synapses were larger than their excitatory counterparts and had fewer glial processes. In freeze-fracture views, inhibitory synapses did not appear as raised plateaus in the P-face as do excitatory synapses, and their active zones were more widely scattered. The intramembrane particles in the inhibitory postsynaptic membrane-representing neurotransmitter receptors-are arranged in parallel rows in the sarcolemmal P-face and have complementary furrows in the sarcolemmal E-face. Altogether, our findings help to describe a population of inhibitory neuromuscular synapses formed by the CI neuron in lobster muscle.     

Effect of spore concentration on germination and autotropism inTrichoderma hamatum

Summary The effect of spore concentration on spore germination and germtube growth ofTrichoderma hamatum on water agar and on potato dextrose agar (PDA) was studied. Increasing inoculum size up to 10⁹ spores/plate on PDA and up to 10⁷ spores/plate on water agar shortened the incubation period required for germtubes emergence and increased germination rate. However, on water agar germination was inhibited at 10⁸ and was completely arrested at 10⁹ spores/plate. Inhibition in germination of 10⁷ spores/plate was observed on water agar when the plates were preincubated with 10⁹ spores/plate for 5 h or more. Addition of glucose and ammonium nitrate to the water agar medium allowed only 25% of the spores to germinate at 10⁹ as compared to 78% at 10⁷ spores/plate after 8 h of incubation. Addition of polysaccharides to the C+N supplemented medium, significantly increased germination up to 84% as compared to 100% on PDA, after 8 h of incubation. Germlings ofTrichoderma hamatum phialospores exhibited positive autotropism and anastamosis on both media. The phenomenon was positively related to inoculum size, being most pronounced at 10⁷ spores/plate.     

四种圆斑蝰蛇蛇毒对血小板聚集抑制作用的比较研究

对四种不同来源的RVV对ADP、Col和Ris诱导的血小板聚集抑制作用进行比较研究。RVV-B,RVVS和RVV-Styp对三种诱导剂的血小板聚集均有抑制作用,而RVV-T虽有ADP和Col抑制作用,但缺乏对Ris的抑制活性。预先与RVV孵育的血小板经洗涤后重新悬浮于自身PPP中,与RVV-StyP孵育的血小板完全恢复对Ris的凝集反应,而与RVV-B和RVV-S孵育的血小板仅部分恢复其反应。上述结果表明,在RVV中可能含有二种不同的血小板聚集抑制活性,而其抑制机理可能牵涉到血小板、血浆等因素。     

Comparison of the susceptibility of porcine and human dipeptidyl-peptidase IV to inhibition by protein-derived peptides

The enzyme dipeptidyl-peptidase IV (DPP-IV) is recognized to be a promising target for the management of type 2 diabetes. Over the last decade, numerous synthetic molecules and more recently, peptides from dietary proteins, have been reported to be able to inhibit DPP-IV activity. Most studies that have investigated the in vitro effect of these inhibitors have used porcine or human DPP-IV. Although structurally alike, it is unclear whether these two species display similar inhibition patterns. Therefore, the objective of this study was to compare the effects of protein-derived peptides on the activity of porcine and recombinant human DPP-IV. The two species showed different inhibition susceptibility to 43 of the 62 peptide sequences investigated. While 37 protein-derived peptides were more effective at inhibiting the porcine DPP-IV, only six caused a stronger inhibition of the activity of the human enzyme. Although the peptides WR, IPIQY and WCKDDQNPHS were found to be among the most potent inhibitors of both species, the inhibitory effect was greater on the porcine enzyme than on human DPP-IV (αK_i or K_i = 11.5, 13.4, 13.3 μM and 31.4, 28.2, 75.0 μM for porcine and human DPP-IV, respectively). Investigation into the mode of action of the most effective inhibitory peptides revealed that both species were inhibited in a similar manner by short fragments (≤5 amino acid residues), but that some of the longer peptides acted differently on the enzymes. This study shows that porcine DPP-IV is generally inhibited with greater potency by protein-derived peptides than is the human enzyme.     

Evidence for the Presence of Serotonin Receptors Negatively Coupled to Adenylate Cyclase in the Rabbit Iris-Ciliary Body

Serotonin has no obvious effect on basal cyclic AMP levels but reduces the forskolin-, isoproterenol-, and vasoactive intestinal peptide-induced stimulation of cyclic AMP levels in a dose-dependent manner. Serotonergic, cholinergic, muscarinic, alpha-adrenergic, and dopaminergic antagonists have no effect on the serotonin response. Topical application of a serotonin/pargyline solution to the living eye causes desensitisation of the serotonin response in the iris-ciliary body, an observation confirming the presence of specific serotonergic receptors linked to adenylate cyclase. The 5-HT1A [5-hydroxytryptamine (serotonin) type 1A] receptor agonists 8-hydroxy-2-(di-n-propylamino)tetralin and buspirone mimic the serotonin response in reducing the forskolin-stimulated cyclic AMP levels, as do the indole derivatives 5-methoxytryptamine, 5-hydroxtryptophan, and tryptamine. However, the ineffectiveness of the 5-HT1A agonist ipsapirone and the inability of spiroxatrine to block the serotonin response show that classical 5-HT1A receptors are not involved. The serotonin response is blocked by pertussis toxin and is insensitive to the phosphodiesterase inhibitor theophylline, which indicates the involvement of an inhibitory guanine regulatory protein in the coupling of the serotonin receptor to the adenylate cyclase catalytic unit.     

Development of 99mTc radiolabeled A85380 derivatives targeting cerebral nicotinic acetylcholine receptor: Novel radiopharmaceutical ligand 99mTc-A-YN-IDA-C4

Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels that have been implicated in higher brain functions. To elucidate the functional mechanisms underlying nAChRs and contribute significantly to development of drugs targeting neurological and neuropsychiatric diseases, non-invasive nuclear medical imaging can be used for evaluation. In addition, technetium-99m (^99mTc) is a versatile radionuclide used clinically as a tracer in single-photon emission computed tomography. Because A85380 is known as a potent α4β2-nAChR agonist, we prepared A85380 derivatives labeled with ^99mTc using a bifunctional chelate system. A computational scientific approach was used to design the probe efficiently. We used non-radioactive rhenium (Re) for a ^99mTc analog and found that one of the derivatives, Re-A-YN-IDA-C4, exhibited high binding affinity at α4β2-nAChR in both the docking simulation (?19.3 kcal/mol) and binding assay (Ki = 0.4 ± 0.04 nM). Further, ^99mTc-A-YN-IDA-C4 was synthesized using microwaves, and its properties were examined. Consequently, we found that ^99mTc-A-YN-IDA-C4, with a structure optimized by using computational chemistry techniques, maintained affinity and selectivity for nAChR in vitro and possessed efficient characteristics as a nuclear medicine molecular imaging probe, demonstrated usefulness of computational scientific approach for molecular improvement strategy.     

Mode of action of acidocin D20079, a bacteriocin produced by the potential probiotic strain, <Emphasis Type="Italic">Lactobacillus acidophilus</Emphasis> DSM 20079

Lactobacillus acidophilus DSM 20079 is the producer of a novel bacteriocin termed acidocin D20079. In this paper, mode of action using three various concentrations of acidocin D20079 (2,048, 128 and 11.3 AU/ml) was determined against an indicator strain L. delbrueckii subsp. lactis DSM 20076. These concentrations all led to marked decreases in both the number of viable cells and in optical density, indicating that the activity of the acidocin D20079 was bactericidal with concomitant cell lysis. Moreover, the probiotic potential of L. acidophilus DSM 20079 was analyzed for its ability to survive and retain viability at conditions (acid and bile concentrations) mimicking the gastrointestinal (GI) tract, under which it survived exposure to pH 2.0 with a 1.2 log cycle reduction in viability and where 45% of the original population survived in a medium containing 0.3% bile for 3 h.     

Distinct peptide binding specificities of Src homology 3 (SH3) protein domains can be determined by modulation of local energetics across the binding interface

The yeast Nbp2p SH3 and Bem1p SH3b domains bind certain target peptides with similar high affinities, yet display vastly different affinities for other targets. To investigate this unusual behavior, we have solved the structure of the Nbp2p SH3-Ste20 peptide complex and compared it with the previously determined structure of the Bem1p SH3b bound to the same peptide. Although the Ste20 peptide interacts with both domains in a structurally similar manner, extensive in vitro studies with domain and peptide mutants revealed large variations in interaction strength across the binding interface of the two complexes. Whereas the Nbp2p SH3 made stronger contacts with the peptide core RXXPXXP motif, the Bem1p SH3b domain made stronger contacts with residues flanking the core motif. Remarkably, this modulation of local binding energetics can explain the distinct and highly nuanced binding specificities of these two domains.     

KCNE3 is an inhibitory subunit of the Kv4.3 potassium channel

The mammalian Kv4.3 potassium channel is a fast activating and inactivating K+ channel widely distributed in mammalian tissues. Kv4.3 is the major component of various physiologically important currents ranging from A-type currents in the CNS to the transient outward potassium conductance in the heart (I(to)). Here we show that the KCNE3 beta-subunit has a strong inhibitory effect on current conducted by heterologously expressed Kv4.3 channels. KCNE3 reduces the Kv4.3 current amplitude, and it slows down the channel activation and inactivation as well as the recovery from inactivation. KCNE3 also inhibits currents generated by Kv4.3 in complex with the accessory subunit KChIP2. We find the inhibitory effect of KCNE3 to be specific for Kv4.3 within the Kv4 channel family. Kv4.3 has previously been shown to interact with a number of beta-subunits, but none of the described subunit-interactions exert an inhibitory effect on the Kv4.3 current.