KCNQ/Kv7 channel regulation of hippocampal gamma-frequency firing in the absence of synaptic transmission. (57/273)

Synchronous neuronal firing can be induced in hippocampal slices in the absence of synaptic transmission by lowering extracellular Ca2+ and raising extracellular K+. However, the ionic mechanisms underlying this nonsynaptic synchronous firing are not well understood. In this study we have investigated the role of KCNQ/Kv7 channels in regulating this form of nonsynaptic bursting activity. Incubation of rat hippocampal slices in reduced (<0.2 mM) [Ca2+]o and increased (6.3 mM) [K+]o, blocked synaptic transmission, increased neuronal firing, and led to the development of spontaneous periodic nonsynaptic epileptiform activity. This activity was recorded extracellularly as large (4.7 +/- 1.9 mV) depolarizing envelopes with superimposed high-frequency synchronous population spikes. These intraburst population spikes initially occurred at a high frequency (about 120 Hz), which decayed throughout the burst stabilizing in the gamma-frequency band (30-80 Hz). Further increasing [K+]o resulted in an increase in the interburst frequency without altering the intraburst population spike frequency. Application of retigabine (10 microM), a Kv7 channel modulator, completely abolished the bursts, in an XE-991-sensitive manner. Furthermore, application of the Kv7 channel blockers, linopirdine (10 microM) or XE-991 (10 microM) alone, abolished the gamma frequency, but not the higher-frequency population spike firing observed during low Ca2+/high K+ bursts. These data suggest that Kv7 channels are likely to play a role in the regulation of synchronous population firing activity.  (+info)

Regulation of growth of mouse mastocytoma cells. (58/273)

N6,O2'-Dibutyryladenosine cyclic 3',5'-phosphate plus theophylline inhibited the growth of the mouse mast cell tumor line PY 815 both in vivo and in vitro. The inhibitory effect on growth in vitro was rapidly reversed following removal of the drugs. Growth inhibition was accompanied by reduced cell surface activity and increased cell-cell adhesion. The drug-treated cells accumulated distinct membrane-bound granules, which are characteristic of more mature mast cells. Treated cells also developed increased amounts of surface-associated acidic mucopolysaccharides. These results suggest that increased intracellular cyclic adenosine 3':5'-monophosphate causes mouse mastocytoma cells to decrease growth and elicits the expression of a more differentiated mast cell phenotype. The effect of the antileukemia drug, 4'-(9-acridinylamino)methanesulfon-m-anisidine, on cyclic adenosine 3':5'-monophosphate and adenosine 5'-triphosphate in mastocytoma cells is also reported.  (+info)

Urinary excretion of free toluenediamines in a patient with polyurethane-covered breast implants. (59/273)

We report the detection of free 2,4-toluenediamine in urine of a patient implanted with polyurethane-covered breast implants. Samples were collected on several dates, ranging from 21 days to seven months after the insertion of the implants, and these samples all showed the presence of free 2,4-toluenediamine at a concentration of about 1 micrograms/L. The chemical was not found in a urine sample collected before implantation. This finding is important for risk assessment of cancer in patients with this type of breast implant because the chemical is a suspected carcinogen. Free 2,6-toluenediamine, an isomer, was also found in all samples from this patient.  (+info)

Gemcitabine plus CI-994 offers no advantage over gemcitabine alone in the treatment of patients with advanced pancreatic cancer: results of a phase II randomized, double-blind, placebo-controlled, multicenter study. (60/273)

BACKGROUND: CI-994, an oral histone deacetylase inhibitor, has antineoplastic activity and synergism with gemcitabine preclinically. This randomized phase II trial explored whether CI-994 plus gemcitabine improves overall survival, objective response, duration of response, time to treatment failure and change in quality of life (QoL) or pain compared with gemcitabine alone. PATIENTS AND METHODS: A total of 174 patients received CG (CI-994 6 mg/m(2)/day days 1-21 plus gemcitabine 1000 mg/m(2) days 1, 8 and 15 each 28-day cycle) or PG (placebo plus gemcitabine 1000 mg/m(2) days 1, 8 and 15 of each 28-day cycle days 1-21). RESULTS: Median survival was 194 days (CG) versus 214 days (PG) (P = 0.908). The objective response rate with CG was 12% versus 14% with PG when investigator-assessed and 1% versus 6%, respectively, when assessed centrally. Time to treatment failure did not differ between the two arms (P = 0.304). QoL scores at 2 months were worse with CG than with PG. Pain response rates were similar between the two groups. There was an increased incidence of neutropenia and thrombocytopenia with CG. CONCLUSIONS: Adding CI-994 to gemcitabine in advanced pancreatic carcinoma does not improve overall survival, response rate or time to progression; CG produced decreased QoL and increased hematological toxicity and appears inferior to single-agent gemcitabine.  (+info)

The KCNQ channel opener retigabine inhibits the activity of mesencephalic dopaminergic systems of the rat. (61/273)

Homo- and heteromeric complexes of KCNQ channel subunits are the molecular correlate of the M-current, a neuron-specific voltage-dependent K(+) current with a well established role in control of neural excitability. We investigated the effect of KCNQ channel modulators on the activity of dopaminergic neurons in vitro and in vivo in the rat ventral mesencephalon. The firing of dopaminergic neurons recorded in mesencephalic slices was robustly inhibited in a concentration-dependent manner by the KCNQ channel opener N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester (retigabine). The effect of retigabine persisted in the presence of tetrodotoxin and simultaneous blockade of GABA(A) receptors, small-conductance calcium-activated K(+) (SK) channels, and hyperpolarization-activated (I(h)) channels, and it was potently reversed by the KCNQ channel blocker 4-pyridinylmethyl-9(10H)-anthracenone (XE991), indicating a direct effect on KCNQ channels. Likewise, in vivo single unit recordings from dopaminergic neurons revealed a prominent reduction in spike activity after systemic administration of retigabine. Furthermore, retigabine inhibited dopamine synthesis and c-Fos expression in the striatum under basal conditions. Retigabine completely blocked the excitatory effect of dopamine D(2) autoreceptor antagonists. Again, the in vitro and in vivo effects of retigabine were completely reversed by preadministration of XE991. Dual immunocytochemistry revealed that KCNQ4 is the major KCNQ channel subunit expressed in all dopaminergic neurons in the mesolimbic and nigrostriatal pathways. Collectively, these observations indicate that retigabine negatively modulates dopaminergic neurotransmission, likely originating from stimulation of mesencephalic KCNQ4 channels.  (+info)

Kv7/KCNQ/M-channels in rat glutamatergic hippocampal axons and their role in regulation of excitability and transmitter release. (62/273)

M-current (I(M)) plays a key role in regulating neuronal excitability. Mutations in Kv7/KCNQ subunits, the molecular correlates of I(M), are associated with a familial human epilepsy syndrome. Kv7/KCNQ subunits are widely expressed, and I(M) has been recorded in somata of several types of neurons, but the subcellular distribution of M-channels remains elusive. By combining field-potential, whole-cell and intracellular recordings from area CA1 in rat hippocampal slices, and computational modelling, we provide evidence for functional M-channels in unmyelinated axons in the brain. Our data indicate that presynaptic M-channels can regulate axonal excitability and synaptic transmission, provided the axons are depolarized into the I(M) activation range (beyond approximately -65 mV). Here, such depolarization was achieved by increasing the extracellular K(+) concentration ([K(+)](o)). Extracellular recordings in the presence of moderately elevated [K(+)](o) (7-11 mm), showed that the specific M-channel blocker XE991 reduced the amplitude of the presynaptic fibre volley and the field EPSP in a [K(+)](o)-dependent manner, both in stratum radiatum and in stratum lacknosum moleculare. The M-channel opener, retigabine, had opposite effects. The higher the [K(+)](o), the greater the effects of XE991 and retigabine. Similar pharmacological modulation of EPSPs recorded intracellularly from CA1 pyramidal neurons, while blocking postsynaptic K(+) channels with intracellular Cs(+), confirmed that active M-channels are located presynaptically. Computational analysis with an axon model showed that presynaptic I(M) can control Na(+) channel inactivation and thereby affect the presynaptic action potential amplitude and Ca(2+) influx, provided the axonal membrane potential is sufficiently depolarized. Finally, we compared the effects of blocking I(M) on the spike after-depolarization and bursting in CA3 pyramidal neuron somata versus their axons. In standard [K(+)](o) (2.5 mm), XE991 increased the ADP and promoted burst firing at the soma, but not in the axons. However, I(M) contributed to the refractory period in the axons when spikes were broadened by a low dose 4-aminopyridine (200 microm). Our results indicate that functional Kv7/KCNQ/M-channels are present in unmyelinated axons in the brain, and that these channels may have contrasting effects on excitability depending on their subcellular localization.  (+info)

A matrix of 3,4-diaminobenzophenone for the analysis of oligonucleotides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. (63/273)

A new matrix of 3,4-diaminobenzophenone (DABP) was demonstrated to be advantageous in the analysis of oligonucleotides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. With DABP as a matrix, intact oligonucleotide ions can be readily produced with lower laser powers, resulting in better detection limits, less fragmentation and fewer alkali metal ion adducts compared with the results obtained with conventional matrices. Importantly, minimal fragmentation and fewer alkali metal ion adducts were seen even at low concentrations of oligonucleotides. It was also found that samples prepared with DABP are highly homogenous and therefore reducing the need for finding 'sweet' spots in MALDI. In addition, excellent shot-to-shot reproducibility, resolution and signal-to-noise ratio were seen with DABP as the matrix.  (+info)

Microbial transformation of aniline derivatives: regioselective biotransformation and detoxification of 2-phenylenediamine by Bacillus cereus strain PDa-1. (64/273)

A bacterial isolate, strain PDa-1, grew well on basal medium supplemented with 2-phenylenediamine, sucrose, and ammonium nitrate and completely transformed 2-phenylenediamine. The isolate was identified as Bacillus cereus. The product formed from 2-phenylenediamine was identified by EI-MS and NMR as 2-aminoacetanilide; whole cells converted 2-phenylenediamine to the product with a 76% molar yield. Whole cells also showed a broad substrate specificity toward 20 of 26 tested arylamines with substituent groups of various size and positions. Especially 2-aminobenzoic acid, 4-aminosalicylic acid, 5-aminosalicylic acid, and 2-aminofluorene were converted completely to the corresponding product with an aminoacetyl group. Cell extracts of strain PDa-1 had a high arylamine N-acetyltransferase activity. The partially purified enzyme converted 2-phenylenediamine to 2-aminoacetanilide. Strain PDa-1 constitutively expressed the enzyme in the absence of 2-phenylenediamine. Effects of 2-phenylenediamine and 2-aminoacetanilide on growth indicated that this enzyme probably plays a role in the detoxification of toxic arylamines in this strain.  (+info)