BAY K 8644, a 1,4-Dihydropyridine Ca2+ Channel Activator: Dissociation of Binding and Functional Effects in Brain Synaptosomes

K+-stimulated 45Ca2+ uptake into rat brain and guinea pig cerebral cortex synaptosomes was measured at 10 s and 90 s at K+ concentrations of 5-75 mM. Net increases in 45Ca2+ uptake were observed in rat and guinea pig brain synaptosomes. 45Ca2+ uptake under resting or depolarizing conditions was not increased by the 1,4-dihydropyridine BAY K 8644, which has been shown to activate Ca2+ channels in smooth and cardiac muscle. High-affinity [3H]nitrendipine binding in guinea pig synaptosomes (KD = 1.2 X 10(-10) M, Bmax = 0.56 pmol mg-1 protein) was competitively displaced with high affinity (IC50 2.3 X 10(-9) M) by BAY K 8644. Thus high-affinity Ca2+ channel antagonist and activator binding sites exist in synaptosome preparations, but their relationship to functional Ca2+ channels is not clear.     

The mechanism-based inactivation of p450 2B4 by tert-butyl 1-methyl-2-propynyl ether: structural determination of the adducts to the p450 heme

tert-Butyl 1-methyl-2-propynyl ether (tBMP) was analyzed for its ability to act as a mechanism-based inactivator of p450 2B4. tBMP inactivated p450 2B4 in a time-, concentration-, and NADPH-dependent manner. Losses in activity occurred with concurrent losses in the reduced CO spectrum and native p450 heme; however, there was a greater loss in activity than could be accounted for by reduced CO spectra or native heme loss. LC/MS analysis demonstrated that the losses in native heme were accompanied by the appearance of two modified hemes with m/z values of 705Da, consistent with tBMP adducted hemes. Both adducts had identical fragmentation patterns when analyzed by LC/MS/MS. The spectra were consistent with a tBMP molecule and an oxygen atom attached to iron-depleted heme. Proton NMR studies suggest that the two modified hemes in p450 2B1 are N-alkylated on pyrrole rings A and D.     

K14、K19在寻常型银屑病发病中的作用机制研究

目的:研究细胞角蛋白K14、K19在寻常型银屑病(PV)发病中的作用机制。方法:选择从2012年1月到2016年12月在西安交通大学第二附属医院皮肤科就诊的PV患者60例纳入本次研究。将PV患者在皮损区及未受累皮肤区分别取1份皮肤,制成存档蜡块,分别记为PV皮损组和PV未受累皮肤组各60例。另选同期在我院接受外伤手术治疗的健康皮肤60例作为对照组,分析K14、K19在PV中的阳性表达率以及表达水平,分析K14及K19在PV皮损区阳性表达的相关性。结果:各组的K14及K19阳性表达率以及表达水平比较差异有统计学意义(P0.05)。PV皮损组和PV未受累皮肤组的K14阳性表达率及表达水平明显高于对照组,K19阳性表达率及表达水平明显低于对照组,差异有统计学意义(P0.05)。PV皮损组的K14阳性表达率及表达水平明显高于PV未受累皮肤组,K19阳性表达率及表达水平明显低于PV未受累皮肤组,差异有统计学意义(P0.05)。根据Spearman法分析相关性发现,K14及K19在PV皮损区阳性表达中呈负相关(r=-0.871,P=0.000)。结论:K14及K19均在PV发病过程中出现异常表达,其中K14阳性表达较强,而K19阳性表达较弱,二者在PV皮损区阳性表达中呈负相关。临床上可考虑监测K14及K19的阳性表达水平,从而更好地辅助临床诊断及病情的预估,值得临床医师关注与重视。     

Cation Permeability and Selectivity of a Root Plasma Membrane Calcium Channel

Calcium channels in the plasma membrane of root cells fulfill both nutritional and signaling roles. The permeability of these channels to different cations determines the magnitude of their cation conductances, their effects on cell membrane potential and their contribution to cation toxicities. The selectivity of the rca channel, a Ca²⁺-permeable channel from the plasma membrane of wheat (Triticum aestivum L.) roots, was studied following its incorporation into planar lipid bilayers. The permeation of K⁺, Na⁺, Ca²⁺ and Mg²⁺ through the pore of the rca channel was modeled. It was assumed that cations permeated in single file through a pore with three energy barriers and two ion-binding sites. Differences in permeation between divalent and monovalent cations were attributed largely to the affinity of the ion binding sites. The model suggested that significant negative surface charge was present in the vestibules to the pore and that the pore could accommodate two cations simultaneously, which repelled each other strongly. The pore structure of the rca channel appeared to differ from that of L-type calcium channels from animal cell membranes since its ion binding sites had a lower affinity for divalent cations. The model adequately accounted for the diverse permeation phenomena observed for the rca channel. It described the apparent submillimolar K _m for the relationship between unitary conductance and Ca²⁺ activity, the differences in selectivity sequences obtained from measurements of conductance and permeability ratios, the changes in relative cation permeabilities with solution ionic composition, and the complex effects of Ca²⁺ on K⁺ and Na⁺ currents through the channel. Having established the adequacy of the model, it was used to predict the unitary currents that would be observed under the ionic conditions employed in patch-clamp experiments and to demonstrate the high selectivity of the rca channel for Ca²⁺ influx under physiological conditions. Received: 23 August 1999/Revised: 12 November 1999     

Mitogen-activated protein kinase signaling is involved in suramin-induced neurite outgrowth in a neuronal cell line

Suramin is a well-known antitrypanosomal drug and a novel experimental agent for the treatment of several cancers. Previous study showed that suramin is an activator of extracellular signal-regulated kinase (ERK1/2) signaling in several cell lines including Chinese hamster ovary cells, although the physiological relevance of this activation remains uncertain. Here, it was shown that suramin enhances neurite outgrowth concomitant with activation of ERK1/2 in Neuro-2a cells, a neuronal cell line. These neurite outgrowth and ERK1/2 activation were significantly inhibited by PD98059, an inhibitor of mitogen-activated protein kinase kinase, as well as by activation of endogenous adenosine A2A receptors. The suramin-induced phosphorylation of ERK1/2 was also inhibited by inhibitors of Src family kinases. This attenuation of ERK1/2 activity was accompanied by a significant decrease in suramin-induced neurite outgrowth. These results suggest that suramin activates the Src/ERK1/2 signaling pathway that induces neurite outgrowth, both of which are negatively regulated by cAMP produced in response to activation of endogenous adenosine A2A receptors.     

Adaptation of signature-tagged mutagenesis to Escherichia coli K1 and the infant-rat model of invasive disease

With the exception of the polysialic acid capsule (K1 antigen), little is known about other virulence factors needed for systemic infection by Escherichia coli K1, the leading cause of Gram-negative neonatal meningitis in humans. In this work, the functional genomics method of signature-tagged mutagenesis (STM) was adapted to E. coli K1 and the infant-rat model to identify non-capsule virulence genes. Validation of the method was demonstrated by the failure to recover a reconstructed acapsular mutant from bacterial pools used to systemically infect 5-day-old rats. Three new genes required for systemic disease were identified from a total of 192 mutants screened by STM (1.56% hit rate). Gut colonization, Southern blot hybridization, mixed-challenge infection, and DNA sequence analyses showed that the attenuating defects in the mutants were associated with transposon insertions in rfaL (O antigen ligase), dsbA (thiol:disulfide oxidoreductase), and a new gene, puvA (previously unidentified virulence gene A), with no known homologues. The results indicate the ability of STM to identify novel systemic virulence factors in E. coli K1.     

Nutritional imbalance in wheat (Triticum aestivum L.) genotypes grown at soil water stress

An experiment was conducted to determine the effect of water stress on nutritional changes in tolerant (DS-4 and Chakwal-86) and susceptible (DS-17 and Pavon) genotypes in lysimeters. The stress was imposed at different growth stages (pre-anthesis, post-anthesis, terminal drought). The biomass (dry weight) and Ca, Mg and P concentration decreased with water stress in all the wheat genotypes. However, the tolerant genotypes had less reduction than susceptible at all the treatments. Potassium increased in all wheat genotypes due to water stress and was higher in tolerant than susceptible genotypes. Sodium content was not affected by water stress.     

Ginkgo biloba extract modifies hypoglycemic action of tolbutamide via hepatic cytochrome P450 mediated mechanism in aged rats

We examined hepatic cytochrome P450 (CYP)-mediated interactions between Ginkgo biloba extract (GBE) and tolbutamide, an oral anti-diabetic agent, in aged and young rats. Tolbutamide was orally given to rats with or without GBE treatment, and time-dependent changes in blood glucose were monitored. The basal activity of six CYP subtypes in liver was lower in the aged rats than in the young rats, while the inductions of these enzymes by 5 day pretreatment of 0.1% GBE diet were more in the aged rats. Further, the pretreatment of GBE significantly attenuated the hypoglycemic action of tolbutamide in the aged rats, corresponding well to the enhanced activity of (S)-warfarin 7-hydroxylase, which is responsible for CYP2C9 subtype, a major isoform metabolizing tolbutamide. In contrast, the simultaneous administration of GBE with tolbutamide potentiated the hypoglycemic action of this drug. The in vitro experiments revealed that GBE competitively inhibited the metabolism of tolbutamide by (S)-warfarin 7-hydroxylase in the rat liver microsomes. In the young rats, the 5 day pretreatment with GBE significantly attenuated the hypoglycemic action of tolbutamide, but a simultaneous treatment had little influence on the tolbutamide effect. In conclusion, the present study has shown that the simultaneous and continuous intake of GBE significantly affects the hypoglycemic action of tolbutamide, possibly via a hepatic CYP enzyme-mediated mechanism, particularly in the aged rats. Therefore, it is anticipated that the intake of GBE as a dietary supplement with therapeutic drugs should be cautious, particularly in elderly people.     

Pharmacokinetic,metabolic stability,plasma protein binding and CYP450s inhibition/induction assessment studies of N-(2-pyridylmethyl)-2-hydroxiymethyl-1-pyrrolidinyl-4-(3-chloro-4-methoxy-benzylamino)-5-pyrimidine-carboxamide as potential type 5 phosphodiesterase inhibitors

N-(2-pyridylmethyl)-2-hydroxiymethyl-1-pyrrolidinyl-4-(3-chloro-4-methoxy-benzylamino)-5-pyrimidine-carboxamide (NHPPC) is a new potential of type 5 phosphodiesterase (PDE5) inhibitors, synthesized from the avanafil analogue for the treatment of erectile dysfunction. The targets of this article were to assess plasma protein binding, liver microsomal metabolic stability, inhibition and induction on cytochrome P450 isozymes and the pharmacokinetics of NHPPC. Equilibrium dialysis technique was applied to determine Plasma protein binding (PPB) and NHPPC was evaluated in male Sprague–Dawley rats and Beagle dogs in vivo pharmacokinetic. The NHPPC was highly bound to plasma proteins in rats, dogs and human tested and the mean values for PPB rate were 96.2%, 99.6% and 99.4%, respectively. After in vitro liver microsomes incubated for 60?min, the percent remaining of NHPPC was 42.8%, 0.8% and 42.0% in rats, dogs and human, respectively. In vitro intrinsic clearance was found to be 0.0233, 0.1204 and 0.0214 mL/min/mg protein in rat, dog and human liver microsomes of NHPPC, respectively. NHPPC showed no significant inhibitory effects on major CYP450 enzymes, and had no significant induction potential on CYP1A2 and CYP3A4. Following oral administration in rats and dogs, t_max was 6 and 0.5?h, respectively. The clearance for NHPPC was 1.19 and 1.46?L/h/kg in rats and dogs, respectively. And absolute bioavailability in rat and dog were approximately 34.5% and 53.1%, respectively. These results showed that NHPPC has a good development prospect.