A multi-lesional analysis of diffuse idiopathic pulmonary neuroendocrine cell hyperplasia: a single-centre analysis

AIM

To conduct a multi-lesional computed tomography (CT) analysis of diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) patients to determine volumetric changes in lesions over 5 years.

MATERIALS AND METHODS

A retrospective case-note review was undertaken to identify 16 patients with histological and radiological features of DIPNECH between 2012-2021. Area and volume were calculated for 17 sets of lesions identified on high-resolution CT. Clinical data were extracted from electronic patient records, which included demographic data, outpatient clinic letters, histology reports, and imaging reports.

RESULTS

One hundred and twenty-eight lesions were identified in 16 patients (one male, 15 female) and followed-up annually over a median 1,985 days (range 1,450-2,290). At year 1 follow-up, lesion area ranged from 1-48 mm2, and lesion volume ranged from 8-18,380 mm3; lesion area ranged from 1-45mm2 and lesion volume ranged from 11-17,800 mm3 and year 5. Half (8/16) of the patients had concomitant typical carcinoid tumours and one patient had an atypical carcinoid tumour. No statistically significant correlation (p<0.05) was found between lesion cross-sectional area or volume and duration of follow-up (years and days). No metastatic spread was observed at the time of analysis.

CONCLUSIONS

No significant increase was observed in the size of over 100 lesions in patients with DIPNECH over a 5-year period and no metastasis occurred during the study period affirming the relatively indolent course of the disease.

Native pulmonary valve endocarditis requiring pulmonary valve replacement in adulthood: a case series

Native pulmonary valve endocarditis is a rare phenomenon as native valve endocarditis tends to typically affect the left sided heart valves. However, the right-sided heart valves can be affected in patients with a history of intravenous drug use, whereby the tricuspid valve is most commonly affected. We present two cases who were diagnosed with native pulmonary valve endocarditis in the absence of congenital heart disease. In the first case, the native pulmonary valve endocarditis was probably a derivative of compounding factors of an enlarged underlying pulmonary artery and staphylococcal bacteraemia. In the second case, a common causal organism of native valve endocarditis following dental treatment and the resultant echocardiography findings was of significant interest. In summary, native pulmonary valve endocarditis is relatively rare complication in the adult population, especially in the absence of congenital heart disease.

Off-pump external pericardial patch repair for post-infarct left ventricular free wall rupture: a case series

We describe an off-pump surgical approach to this challenging condition supported by our results from a case series, which would add to existing literature in the management of this life-threatening complication. We identified seven patients who underwent surgical intervention for left ventricular (LV) free wall rupture at our institution. They were all diagnosed to have cardiac tamponade secondary to free wall rupture of the LV in the presence of acute myocardial infarction. The surgical technique comprised of utilizing an external pericardial patch which was secured using surgical biological glues (fibrin-based sealants or gelatin hydrogels). The 30-day mortality, 1-year survival and 2-year survival were 57, 42 and 42%, respectively. Advanced age, female gender and use of cardiopulmonary bypass were characteristics that were not significantly associated with survival. We advocate the use of an off-pump external pericardial patch repair strategy as a ‘bridge to recovery’ in this extremely high-risk group of patients.

Rectal and bladder dose reduction with the addition of intravaginal balloons to vaginal packing in intracavitary brachytherapy for cervical cancer

PURPOSE

The use of intravaginal Foley balloons in addition to conventional packing during high-dose-rate (HDR) tandem and ovoids intracavitary brachytherapy (ICBT) is a means to improve displacement of organs at risk, thus reducing dose-dependent complications. The goal of this project was to determine the reduction in dose achieved to the bladder and rectum with intravaginal Foley balloons with CT-based planning and to share our packing technique.

METHODS AND MATERIALS

One hundred and six HDR-ICBT procedures performed for 38 patients were analyzed for this report. An uninflated Foley balloon was inserted into the vagina above and below the tandem flange separately and secured in place with vaginal packing. CT images were then obtained with both inflated and deflated Foley balloons. Plan optimization occurred and dose volume histogram data were generated for the bladder and rectum. Maximum dose to 0.1, 1.0, and 2.0 cm(3) volumes for the rectum and bladder were analyzed and compared between inflated and deflated balloons using parametric statistical analysis.

RESULTS

Inflation of intravaginal balloons allowed significant reduction of dose to the bladder and rectum. Amount of reduction was dependent on the anatomy of the patient and the placement of the balloons. Displacement of the organs at risk by the balloons allowed an average of 7.2% reduction in dose to the bladder (D0.1 cm(3)) and 9.3% to the rectum (D0.1 cm(3)) with a maximum reduction of 41% and 43%, respectively.

CONCLUSIONS

For patients undergoing HDR-ICBT, a significant dose reduction to the bladder and rectum could be achieved with further displacement of these structures using intravaginal Foley balloons in addition to conventional vaginal packing.

Simultaneous spectrophotometric determination of celecoxib and diacerein in bulk and capsule by absorption correction method and chemometric methods

Two methods, absorption correction and multivariate spectrophotometric methods were developed for simultaneous estimation of Celecoxib (CEL) and Diacerein (DIA) in combined dosage form. Absorption correction method involves direct estimation of DIA at wavelength 341 nm in which CEL has zero absorbance and shows no interference. For estimation of CEL, corrected absorbance was calculated at 253 nm due to the interference of DIA at this wavelength. Linearity was observed in the range of 6-22 μg mL(-1) for CEL and 3-11 μg mL(-1) for DIA. The method was validated as per ICH guidelines. Chemometric methods including classical least square (CLS), inverse least square (ILS), principal component regression (PCR) and partial least square (PLS) were studied for simultaneous determination of CEL and DIA in capsule using spectrophotometry. A set of 25 standard mixtures containing both drugs were prepared in range of 5-25 μg mL(-1) for CEL and 3-15 μg mL(-1) for DIA. Analytical figure of merit (FOM), such as sensitivity, selectivity, analytical sensitivity, limit of detection and limit of quantitation were determined for chemometric methods. The proposed methods were applied for determination of two components from combined dosage form.

Successful percutaneous coronary intervention in a patient with combined deficiency of FV and FVIII due to novel compound heterozygous mutations in LMAN1

Percutaneous coronary intervention (PCI) in patients with congenital coagulation factor deficiencies presents a unique challenge. They are not only at increased risk of perioperative bleeding but can also suffer thrombosis of the stent as preventive anticoagulation and antiplatelet therapy is difficult. Several cases of successful PCI have been described in patients with haemophilia A and B, but there are no reports in patients with combined coagulation factor deficiencies. We used PCI to treat the coronary artery disease in a patient with the combined deficiency of factor V and factor VIII (F5F8D) and analysed the molecular basis of the disorder for this patient. A 68-year-old patient was admitted for urgent PCI with bare metal stent placement after the diagnosis of the F5F8D. Peripheral blood DNA was extracted for the sequence analysis of LMAN1 and MCFD2 genes. Mutations in LMAN1 was confirmed by molecular cloning of the PCR product and resequencing of the resulting clones. The patient underwent successful PCI with good long-term outcome. Our patient tolerated anticoagulation therapy well, with unfractionated heparin, and double antiplatelet therapy while he was initially supported with fresh frozen plasma and recombinant FVIII. Molecular analysis revealed that the patient carries unusual compound heterozygous frameshift mutations on the same microsatellite repeat region in exon 8 of LMAN1, one of which is a novel mutation (c.912delA). Our results suggest that patients with F5F8D can safely undergo PCI for coronary artery disease, with the treatment individualized to the specific patient.

Capillary versus venous haemoglobin determination in the assessment of healthy blood donors

BACKGROUND AND OBJECTIVES

To determine the accuracy of fingerstick haemoglobin assessment in blood donors, the performance of a portable haemoglobinometer (HemoCue Hb 201+) was prospectively compared with that of an automated haematology analyzer (Cell-Dyn 4000). Haemoglobin values obtained by the latter were used as the 'true' result.

MATERIAL AND METHODS

Capillary fingerstick samples were assayed by HemoCue in 150 donors. Fingerstick samples from two sites, one on each hand, were obtained from a subset of 50 subjects. Concurrent venous samples were tested using both HemoCue and Cell-Dyn devices.

RESULTS

Capillary haemoglobin values (HemoCue) were significantly greater than venous haemoglobin values (HemoCue), which in turn were significantly greater than venous haemoglobin values by Cell-Dyn (mean ± SD: 14.05 ± 1.51, 13.89 ± 1.31, 13.62 ± 1.23, respectively; P < 0.01 for all comparisons among groups). Nine donors (6%) passed haemoglobin screening criteria (≥ 12.5 g/dl) by capillary HemoCue, but were deferred by Cell-Dyn values (false-pass). Five donors (3%) were deferred by capillary sampling, but passed by Cell-Dyn (false-fail). Substantial variability in repeated fingerstick HemoCue results was seen (mean haemoglobin 13.72 vs. 13.70 g/dl, absolute mean difference between paired samples 0.76 g/dl). Hand dominance was not a factor.

CONCLUSIONS

Capillary samples assessed via a portable device yielded higher haemoglobin values than venous samples assessed on an automated analyzer. False-pass and false-fail rates were low and acceptable in the donor screening setting, with 'true' values not differing by a clinically significant degree from threshold values used to assess acceptability for blood donation.

The unwritten price of cosmetic tourism: an observational study and cost analysis

INTRODUCTION AND AIMS

Cosmetic tourism, driven by the promise of inexpensive operations abroad, is increasingly popular despite warnings from professional bodies regarding associated risks. Increasing numbers of individuals have presented to our department requesting NHS treatment of complications from such surgery. We set out to characterize these patients and evaluate costs incurred through their assessment and management.

MATERIAL AND METHODS

An observational study was conducted from 2007 to 2009 on patients presenting to a tertiary referral Plastic Surgery practice with complications of cosmetic tourism surgery. Demographic characteristics, as well as those related to the operation, were recorded. Hospital patient flow pathways were constructed, cost analysis performed using Patient Level Costing, and expenditure and profitability calculated.

KEY RESULTS

Nineteen patients presented within the study period. Most operations were performed in Europe or Asia, and were primarily breast augmentation procedures (n=13). The principal complications were wound infection or dehiscence, and poor cosmetic results. Eleven patients received NHS treatment, at a cost of £120,841. The mean cost for all patients' management was £6360 (range: £114-£57,968), rising to £10,878 for those accepted for treatment. For 8 of the 9 patients (89%) for whom full patient level costing was available, the hospital incurred a financial loss.

CONCLUSION

The costs to the NHS of managing complications of cosmetic tourism are substantial, and underestimated by central funding agencies.

Multiple myeloma presenting as solitary mass in the posterior fossa

Intracranial plasma cell tumors are extremely rare and can either be solitary lesions or part of systemic multiple myeloma. We report a 42-year-old woman who presented with a posterior fossa mass and successfully underwent surgical resection, leading to the diagnosis of multiple myeloma. To our knowledge, this is the first reported case of multiple myeloma presenting as a posterior fossa mass lesion. This report highlights the importance of maintaining plasma cell tumor in the differential of intracranial mass with bony involvement. Furthermore, once the diagnosis is established, further work up is critical to evaluate for systemic disease.

Up- and down-regulation of the mechano-gated K(2P) channel TREK-1 by PIP (2) and other membrane phospholipids

TREK-1 is an unconventional K(+) channel that is activated by both physical and chemical stimuli. In this study, we show that the inner leaflet membrane phospholipids, including PIP(2), exert a mixed stimulatory and inhibitory effect on TREK-1. Intra-cellular phospholipids inhibit basal channel activity and activation by membrane stretch, intra-cellular acidosis and arachidonic acid. However, binding of endogenous negative inner leaflet phospholipids with poly-lysine reduces inhibition and reveals channel stimulation by exogenous intra-cellular phospholipids. A similar effect is observed with PI, PE, PS and PA, unlike DG, demonstrating that the phosphate at position 3 is required although the global charge of the molecule is not critical. Inhibition depends on the distal C-terminal domain that conditions channel mechano-sensitivity, but is independent of the positively charged PIP(2) stimulatory site in the proximal C-terminal domain. This is, to our knowledge, the first report of an ion channel dually regulated by membrane phospholipids.

Cardiovascular polycystins: insights from autosomal dominant polycystic kidney disease and transgenic animal models

Mutations in the PKD1 and PKD2 polycystin genes are responsible for autosomal dominant polycystic kidney disease (ADPKD), one of the most prevalent genetic kidney disorders. ADPKD is a multisystem disease characterized by the formation of numerous fluid-filled cysts in the kidneys, the pancreas, and the liver. Moreover, major cardiovascular manifestations are common complications in ADPKD. Intracranial aneurysms and arterial hypertension are among the leading causes of mortality in this disease. In the present review, we summarize our current understanding of the role of polycystins in the development, maintenance, and function of the cardiovascular system.

Desensitization of mechano-gated K2P channels

The neuronal mechano-gated K2P channels TREK-1 and TRAAK show pronounced desensitization within 100 ms of membrane stretch. Desensitization persists in the presence of cytoskeleton disrupting agents, upon patch excision, and when channels are expressed in membrane blebs. Mechanosensitive currents evoked with a variety of complex stimulus protocols were globally fit to a four-state cyclic kinetic model in detailed balance, without the need to introduce adaptation of the stimulus. However, we show that patch stress can be a complex function of time and stimulation history. The kinetic model couples desensitization to activation, so that gentle conditioning stimuli do not cause desensitization. Prestressing the channels with pressure, amphipaths, intracellular acidosis, or the E306A mutation reduces the peak-to-steady-state ratio by changing the preexponential terms of the rate constants, increasing the steady-state current amplitude. The mechanical responsivity can be accounted for by a change of in-plane area of approximately 2 nm2 between the closed and open conformations. Desensitization and its regulation by chemical messengers is predicted to condition the physiological role of K2P channels.

Cross-talk between the mechano-gated K2P channel TREK-1 and the actin cytoskeleton

TREK-1 (KCNK2) is a K(2P) channel that is highly expressed in fetal neurons. This K(+) channel is opened by a variety of stimuli, including membrane stretch and cellular lipids. Here, we show that the expression of TREK-1 markedly alters the cytoskeletal network and induces the formation of actin- and ezrin-rich membrane protrusions. The genetic inactivation of TREK-1 significantly alters the growth cone morphology of cultured embryonic striatal neurons. Cytoskeleton remodelling is crucially dependent on the protein kinase A phosphorylation site S333 and the interactive proton sensor E306, but is independent of channel permeation. Conversely, the actin cytoskeleton tonically represses TREK-1 mechano-sensitivity. Thus, the dialogue between TREK-1 and the actin cytoskeleton might influence both synaptogenesis and neuronal electrogenesis.

A phospholipid sensor controls mechanogating of the K+ channel TREK-1

TREK-1 (KCNK2 or K(2P)2.1) is a mechanosensitive K(2P) channel that is opened by membrane stretch as well as cell swelling. Here, we demonstrate that membrane phospholipids, including PIP(2), control channel gating and transform TREK-1 into a leak K(+) conductance. A carboxy-terminal positively charged cluster is the phospholipid-sensing domain that interacts with the plasma membrane. This region also encompasses the proton sensor E306 that is required for activation of TREK-1 by cytosolic acidosis. Protonation of E306 drastically tightens channel-phospholipid interaction and leads to TREK-1 opening at atmospheric pressure. The TREK-1-phospholipid interaction is critical for channel mechano-, pH(i)- and voltage-dependent gating.

An intracellular proton sensor commands lipid- and mechano-gating of the K(+) channel TREK-1

The 2P domain K(+) channel TREK-1 is widely expres sed in the nervous system. It is opened by a variety of physical and chemical stimuli including membrane stretch, intracellular acidosis and polyunsaturated fatty acids. This activation can be reversed by PKA-mediated phosphorylation. The C-terminal domain of TREK-1 is critical for its polymodal function. We demonstrate that the conversion of a specific glutamate residue (E306) to an alanine in this region locks TREK-1 in the open configuration and abolishes the cAMP/PKA down-modulation. The E306A substitution mimics intracellular acidosis and rescues both lipid- and mechano-sensitivity of a loss-of-function truncated TREK-1 mutant. We conclude that protonation of E306 tunes the TREK-1 mechanical setpoint and thus sets lipid sensitivity.

Molecular basis of the voltage-dependent gating of TREK-1, a mechano-sensitive K(+) channel

TREK-1 is a member of the mammalian two P domain K(+) channel family. Mouse TREK-1 activity, in transiently transfected COS cells, is reduced at negative resting membrane potentials by both an external Mg(2+) block and an intrinsic voltage-dependent gating mechanism leading to a strong outward rectification. Deletional and chimeric analysis demonstrates that the carboxy terminal domain of TREK-1, but not the PKA phosphorylation site S333, is responsible for voltage-dependent gating. Since the same region is also critically required for TREK-1 mechano-gating, both mechanisms might be functionally linked. Preferential opening of TREK-1 at depolarized potentials will greatly affect action potential duration, recovery from inactivation and neuronal repetitive firing activity.

Lipid and mechano-gated 2P domain K(+) channels

The two pore domain K(+) channels TREK and TRAAK are opened by membrane stretch. The activating mechanical force comes from the bilayer membrane and is independent of the cytoskeleton. Emerging work shows that mechano-gated TREK and TRAAK are opened by various lipids, including long chain polyunsaturated anionic fatty acids and neutral cone-shaped lysophospholipids. TREK-1 shares the properties of the Aplysia neuronal S channel, a presynaptic background K(+) channel involved in behavioral sensitization, a simple form of learning.

Molecular physiology of oxygen-sensitive potassium channels

Physiological adaptation to acute hypoxia involves oxygen-sensing by a variety of specialized cells including carotid body type I cells, pulmonary neuroepithelial body cells, pulmonary artery myocytes and foetal adrenomedullary chromaffin cells. Hypoxia induces depolarization by closing a specific set of potassium channels and triggers cellular responses. Molecular biology strategies have recently allowed the identification of the K+ channel subunits expressed in these specialized cells. Several voltage-gated K+ channel subunits comprising six transmembrane segments and a single pore domain (Kv1.2, Kv1.5, Kv2.1, Kv3.1, Kv3.3, Kv4.2 and Kv9.3) are reversibly blocked by hypoxia when expressed in heterologous expression systems. Additionally, the background K+ channel subunit TASK-1, which comprises four transmembrane segments and two pore domains, is also involved in both oxygen- and acid-sensing in peripheral chemoreceptors. Progress is currently being made to identify the oxygen sensors. Regulatory beta subunits may play an important role in the modulation of Kv channel subunits by oxygen.

Properties and modulation of mammalian 2P domain K+ channels

Mammalian 2P domain K(+) channels are responsible for background or 'leak' K(+) currents. These channels are regulated by various physical and chemical stimuli, including membrane stretch, temperature, acidosis, lipids and inhalational anaesthetics. Furthermore, channel activity is tightly controlled by membrane receptor stimulation and second messenger phosphorylation pathways. Several members of this novel family of K(+) channels are highly expressed in the central and peripheral nervous systems in which they are proposed to play an important physiological role. The pharmacological modulation of this novel class of ion channels could be of interest for both general anaesthesia and ischaemic neuroprotection.

TWIK-2, an inactivating 2P domain K+ channel

We cloned human and rat TWIK-2 and expressed this novel 2P domain K(+) channel in transiently transfected COS cells. TWIK-2 is highly expressed in the gastrointestinal tract, the vasculature, and the immune system. Rat TWIK-2 currents are about 15 times larger than human TWIK-2 currents, but both exhibit outward rectification in a physiological K(+) gradient and mild inward rectification in symmetrical K(+) conditions. TWIK-2 currents are inactivating at depolarized potentials, and the kinetic of inactivation is highly temperature-sensitive. TWIK-2 shows an extremely low conductance, which prevents the visualization of discrete single channel events. The inactivation and rectification are intrinsic properties of TWIK-2 channels. In a physiological K(+) gradient, TWIK-2 is half inhibited by 0.1 mm Ba(2+), quinine, and quinidine. Finally, cysteine 53 in the M1P1 external loop is required for functional expression of TWIK-2 but is not critical for subunit self-assembly. TWIK-2 is the first reported 2P domain K(+) channel that inactivates. The base-line, transient, and delayed activities of TWIK-2 suggest that this novel 2P domain K(+) channel may play an important functional role in cell electrogenesis.

TREK-1 is a heat-activated background K(+) channel

Peripheral and central thermoreceptors are involved in sensing ambient and body temperature, respectively. Specialized cold and warm receptors are present in dorsal root ganglion sensory fibres as well as in the anterior/preoptic hypothalamus. The two-pore domain mechano-gated K(+) channel TREK-1 is highly expressed within these areas. Moreover, TREK-1 is opened gradually and reversibly by heat. A 10 degrees C rise enhances TREK-1 current amplitude by approximately 7-fold. Prostaglandin E2 and cAMP, which are strong sensitizers of peripheral and central thermoreceptors, reverse the thermal opening of TREK-1 via protein kinase A-mediated phosphorylation of Ser333. Expression of TREK-1 in peripheral sensory neurons as well as in central hypothalamic neurons makes this K(+) channel an ideal candidate as a physiological thermoreceptor.

The neuroprotective agent riluzole activates the two P domain K(+) channels TREK-1 and TRAAK

Riluzole (RP 54274) is a potent neuroprotective agent with anticonvulsant, sedative, and anti-ischemic properties. It is currently used in the treatment of amyotrophic lateral sclerosis. This article reports that riluzole is an activator of TREK-1 and TRAAK, two important members of a new structural family of mammalian background K(+) channels with four transmembrane domains and two pore regions. Whereas riluzole activation of TRAAK is sustained, activation of TREK-1 is transient and is followed by an inhibition. The inhibitory process is attributable to an increase of the intracellular cAMP concentration by riluzole that produces a protein kinase A-dependent inhibition of TREK-1. Mutants of TREK-1 lacking the Ser residue where the kinase A phosphorylation takes place are activated in a sustained manner by riluzole. TRAAK is permanently activated by riluzole because, unlike TREK-1, it lacks the negative regulation by cAMP.

Lysophospholipids open the two-pore domain mechano-gated K(+) channels TREK-1 and TRAAK

The two-pore (2P) domain K(+) channels TREK-1 and TRAAK are opened by membrane stretch as well as arachidonic acid (AA) (Patel, A. J., Honoré, E., Maingret, F., Lesage, F., Fink, M., Duprat, F., and Lazdunski, M. (1998) EMBO J. 17, 4283-4290; Maingret, F., Patel, A. J., Lesage, F., Lazdunski, M., and Honoré, E. (1999) J. Biol. Chem. 274, 26691-26696; Maingret, F., Fosset, M., Lesage, F., Lazdunski, M. , and Honoré, E. (1999) J. Biol. Chem. 274, 1381-1387. We demonstrate that lysophospholipids (LPs) and platelet-activating factor also produce large specific and reversible activations of TREK-1 and TRAAK. LPs activation is a function of the size of the polar head and length of the acyl chain but is independent of the charge of the molecule. Bath application of lysophosphatidylcholine (LPC) immediately opens TREK-1 and TRAAK in the cell-attached patch configuration. In excised patches, LPC activation is lost, whereas AA still produces maximal opening. The carboxyl-terminal region of TREK-1, but not the amino terminus and the extracellular loop M1P1, is critically required for LPC activation. LPC activation is indirect and may possibly involve a cytosolic factor, whereas AA directly interacts with either the channel proteins or the bilayer and mimics stretch. Opening of TREK-1 and TRAAK by fatty acids and LPs may be an important switch in the regulation of synaptic function and may also play a protective role during ischemia and inflammation.

Mechano- or acid stimulation, two interactive modes of activation of the TREK-1 potassium channel

TREK-1 is a member of the novel structural class of K(+) channels with four transmembrane segments and two pore domains in tandem (1,2). TREK-1 is opened by membrane stretch and arachidonic acid. It is also an important target for volatile anesthetics (2,3). Here we show that internal acidification opens TREK-1. Indeed, lowering pH(i) shifts the pressure-activation relationship toward positive values and leads to channel opening at atmospheric pressure. The pH(i)-sensitive region in the carboxyl terminus of TREK-1 is the same that is critically involved in mechano-gating as well as arachidonic acid activation. A convergence, which is dependent on the carboxyl terminus, occurs between mechanical, fatty acids and acidic stimuli. Intracellular acidosis, which occurs during brain and heart ischemia, will induce TREK-1 opening with subsequent K(+) efflux and hyperpolarization.

Inhalational anesthetics activate two-pore-domain background K+ channels

Volatile anesthetics produce safe, reversible unconsciousness, amnesia and analgesia via hyperpolarization of mammalian neurons. In molluscan pacemaker neurons, they activate an inhibitory synaptic K+ current (IKAn), proposed to be important in general anesthesia. Here we show that TASK and TREK-1, two recently cloned mammalian two-P-domain K+ channels similar to IKAn in biophysical properties, are activated by volatile general anesthetics. Chloroform, diethyl ether, halothane and isoflurane activated TREK-1, whereas only halothane and isoflurane activated TASK. Carboxy (C)-terminal regions were critical for anesthetic activation in both channels. Thus both TREK-1 and TASK are possibly important target sites for these agents.

A mammalian two pore domain mechano-gated S-like K+ channel

Aplysia S-type K+ channels of sensory neurons play a dominant role in presynaptic facilitation and behavioural sensitization. They are closed by serotonin via cAMP-dependent phosphorylation, whereas they are opened by arachidonic acid, volatile general anaesthetics and mechanical stimulation. We have identified a cloned mammalian two P domain K+ channel sharing the properties of the S channel. In addition, the recombinant channel is opened by lipid bilayer amphipathic crenators, while it is closed by cup-formers. The cytoplasmic C-terminus contains a charged region critical for chemical and mechanical activation, as well as a phosphorylation site required for cAMP inhibition.

Disruption of mitochondrial respiration inhibits volume-regulated anion channels and provokes neuronal cell swelling

Hypoxia and inhibitors of mitochondrial respiration impair the regulatory volume decrease (RVD) of cerebellar granule neurons after hypotonic swelling. RVD is linked to the opening of volume-regulated anion channels (VRACs). VRACs are outwardly rectifying, inactivate slowly during maintained depolarization, and are permeable to the cellular organic osmolyte taurine. Channel activation requires nonhydrolytic ATP binding and is not modulated by intracellular ADP. VRAC opening is reversibly depressed by hypoxia and by mitochondrial inhibitors such as oligomycin, rotenone, and antimycin A. These results demonstrate that neuronal VRAC activation and swelling are both tightly linked to cellular energy. Moreover, the findings reported in this work may have a particular significance for inherited mitochondrial human diseases, such as mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), which cause brain swelling and edema.

Factors that affect the expression of beta-amyloid precursor protein immunoreactivity in the rat retina

Expression of beta-amyloid precursor protein immunoreactivity in the rat retina was studied after intravitreal injection of substances known to influence neural function in different ways. The substances were the excitatory amino acid glutamate, the inflammatory agent lipopolysaccharide, the depolarizing agent potassium chloride, and the potassium channel blocker barium chloride. In comparison with controls, more beta-amyloid precursor protein immunoreactivity was observed in the radial process of Müller glial cells 24 hours after injection of glutamate or lipopolysaccharide. In contrast, administration of barium chloride greatly reduced immunostaining in Müller cells. Further, an increase in immunostaining was observed in the inner and outer plexiform layers in retinas treated with any of the 3 chemicals, and in blood vessels after injection of glutamate and lipopolysaccharide. These observations suggest that multiple but specific signaling pathways are involved in regulating expression of beta-amyloid precursor protein in distinct cell types and regions in the retina.

Preparation and purification of antisera against different regions or isoforms of beta-amyloid precursor protein

We describe a procedure for the production and peptide affinity purification of polyclonal antisera against synthetic peptides representing different domains of beta-amyloid precursor protein (APP). Rabbits were immunised with keyhole limpet haemocyanin coupled to synthetic peptides representing the amino-terminal APP18-32, Kunitz-type protease inhibitor (KPI) region APP301-316, the A beta region APP670-686, and the carboxy-terminal APP756-770 of APP770 for the production of antisera anti-AP-1, anti-AP-2, anti-AP-4 and anti-AP-5, respectively. Each antiserum was purified to specific antibody using the respective cognate peptides immobilised on affinity columns as ligand, using the 1-ethyl-3-(dimethylaminopropyl)carbodiimide-diaminodipropylamine method. Purified antibodies of these four antisera were highly specific and in enzyme-linked immunosorbent assays (ELISA) reacted only to the corresponding peptide. These purified antisera have been used in Western blot, immunohistochemical and immunoprecipitation techniques to facilitate the understanding of the regulation of APP and amyloid beta-protein (A beta). The A beta is formed by proteolysis of APP, and its deposition leading to the formation of senile plaques in the brain is considered to be a key step in the pathogenesis of Alzheimer's disease.

Kv2.1/Kv9.3, a novel ATP-dependent delayed-rectifier K+ channel in oxygen-sensitive pulmonary artery myocytes

The molecular structure of oxygen-sensitive delayed-rectifier K+ channels which are involved in hypoxic pulmonary artery (PA) vasoconstriction has yet to be elucidated. To address this problem, we identified the Shab K+ channel Kv2.1 and a novel Shab-like subunit Kv9.3, in rat PA myocytes. Kv9.3 encodes an electrically silent subunit which associates with Kv2.1 and modulates its biophysical properties. The Kv2.1/9.3 heteromultimer, unlike Kv2.1, opens in the voltage range of the resting membrane potential of PA myocytes. Moreover, we demonstrate that the activity of Kv2.1/Kv9.3 is tightly controlled by internal ATP and is reversibly inhibited by hypoxia. In conclusion, we propose that metabolic regulation of the Kv2.1/Kv9.3 heteromultimer may play an important role in hypoxic PA vasoconstriction and in the possible development of PA hypertension.

Cell-specific expression of beta-amyloid precursor protein isoform mRNAs and proteins in neurons and astrocytes

The abnormal accumulation of beta-amyloid (A beta) in senile plaques appears to be a central pathological process in Alzheimer's disease. A beta is formed by proteolysis of beta-amyloid precursor protein (APP) with several isoforms generated by alternative splicing of exons 7, 8 and 15. A semi-quantitative reverse transcription (RT)-polymerase chain reaction (PCR) analysis showed that APP695 mRNA lacking exon 7 and 8 was most abundant in primary cultures of rat neurons, while APP770 and APP751 representing, respectively, the full length and exon 8 lacking isoforms predominated in cultured astroglial cells. Antisera AP-2 and AP-4 were produced by immunizing rabbits with keyhole limpet haemocyanin coupled with synthetic peptides representing KPI region APP301-316 and A beta region APP670-686 of APP770, respectively. These polyclonal antisera were purified against the corresponding peptide using affinity chromatography. Western blot analysis of homogenates of relatively enriched neuronal and astroglial cultures showed that these antibodies discretely stained bands of proteins in a cell-specific manner. Dot-blot analysis using AP-2, AP-4 and 22C11 antibodies indicated that, in comparison with neurons, cultured astrocytes contained 3-fold greater KPI-containing APP isoform proteins. The amount of total APP proteins, which include both KPI-containing and KPI-lacking APP isoforms, was approximately 90% higher in astrocytes than in neurons. Consistent with these in vitro findings in cultured astrocytes, in fimbria-fornix lesioned rat hippocampus, labelling with AP-2 antibody, which specifically reacts with KPI-containing APP proteins, was mainly observed in glial fibrillary acidic protein-positive reactive astrocytes in vivo. The results showed that APP isoforms are expressed in a cell type-specific manner in the brain and, since deposition of A beta is closely associated with the expression of KPI-containing APP isoforms, provide further evidence for the involvement of astrocytes in plaque biogenesis.

Presenilins and early-onset familial Alzheimer's disease

Thirty-seven missense mutations and a splice-site mutation in the presenilin gene PS1 on chromosome 14 and two missense mutations PS2 on chromosome 1 co-segregate with early-onset familial Alzheimer's disease (AD). The presenilins belong to a family of conserved integral membrane proteins which include Caenorhabditis elegans SPE4 and SEL12 and the rat apoptosis-linked gene, ALG3. This review summarizes the genetics of presenilins in AD and indicators of putative function based on cellular localization and the functions of non-human homologues. Findings to date suggest an important role of presenilins in beta-amyloid (A beta) production: in vitro and in vivo studies have shown that presenilin mutations are associated with relatively increased production of the longer, and highly fibrillogenic A beta 42(43) peptide, and a marked elevation in the number of A beta 42-immunoreactive plaques in the brains of individuals with familial AD who carry PS1 and PS2 mutations. There is growing evidence that the deposition of A beta 42(43) could in some cases be an early and key event in the AD pathogenic cascade. The genetic and molecular biological data discussed in this review describe mechanisms by which presenilin mutations could lead to the development of AD. Also, mutant presenilins may be more proapoptotic. It is argued that the understanding of the processes by which presenilin mutations lead to the development of AD will help in devising a coherent framework for therapeutic strategies.

Expression of beta-amyloid precursor protein immunoreactivity in the retina of the rat during normal development and after neonatal optic tract lesion

Immunoreactivity to beta-amyloid precursor protein (APP) was present in the inner plexiform, ganglion cell and optic fibre layers, as well as in blood vessels, at birth in normally developing rat retinas. In the inner plexiform layer immunoreactivity disappeared by postnatal day (P) 14. A small population of ganglion cells was immunoreactive at birth, but none were visible at P7. From P14 onwards, however, there was weak immunoreactivity in ganglion cells again, and strong staining in Müller glia. Retinas affected by neonatal optic tract lesions contained more immunoreactive ganglion cells at P4 than did controls, but by P14 there was a severe loss of ganglion cells. These observations are consistent with APP being involved in retinal differentiation, including maturation of glia and neurones, synaptogenesis and possibly neuronal survival.

Glial cell derived neurotrophic factors and Alzheimer's disease

In Alzheimer's disease the normal balance of metabolic pathways regulating trophic factors/cytokines is disrupted; local reduction may result in neurons being deprived of neurotrophic factors while an excess may initiate a cascade of interaction between glial cells and beta-amyloid precursor protein metabolism thereby facilitating plaque formation. This paper briefly discusses the findings of our group on aspects ranging from cholinergic humoral and trophic factors to mechanisms underlying amyloidogenesis in Alzheimer's disease.

Modulation of N-methyl-D-aspartate receptor mediated arachidonic acid release by endogenous nitric oxide in cultured neurons

Nitric oxide (NO) and arachidonic acid (AA) are believed to act as intra- and intercellular messengers in the central nervous system. Using primary cultures of striatal and hippocampal neurons, we have studied the effect of endogenous NO on N-methyl-D-aspartate (NMDA)-mediated AA release. Inhibition of NO synthesis with L-NG-nitroarginine (L-Noarg) produced a dose-dependent increase in NMDA-mediated AA release that was reversed by L-arginine. On the other hand, L-Noarg did not modify AA release produced by joint stimulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and phospholipase C-coupled metabotropic subtypes of glutamate receptors. Our results indicate that endogenously produced NO could modulate cellular events mediated by NMDA-induced AA release.

beta-Amyloid-mediated inhibition of redox activity (MTT reduction) is not an indicator of astroglial degeneration

The reduction in 3-[4,5-dimethylthiazol]-2,5-diphenyltetrazolium bromide (MTT) to a coloured formazan compound by cultured cells has been extensively used as an in vitro model for understanding neurobiological mechanisms involved in amyloid beta-protein (A beta-mediated cell death. In primary cultures of astrocytes, very low concentrations of aggregated A beta 1-4C, but not A beta 4C-1, produced a significant inhibition in the reduction of the dye MTT. This inhibitory response was rapid and persisted as long as A beta 1-4C was present in the culture medium. Such a severe reduction in cell redox activity for days failed to cause death of astroglial cells, measured in terms of trypan blue uptake and lactate dehydrogenase release. Interleukin-1 beta (IL-1 beta), which is known to attenuate excitotoxic neurodegeneration, had no effect on A beta 1-4C-induced inhibition of MTT reduction. These results suggest that even though inhibition of MTT reduction represents an early indicator of the A beta 1-4C mediated cell injury, without other corroborating evidence, it should not be used as a measure of cell death.

v-Abl activates c-myc transcription through the E2F site

The v-abl oncogene of Abelson murine leukemia virus encodes a deregulated form of the cellular nonreceptor tyrosine kinase. v-Abl activates c-myc transcription, and c-Myc is an essential downstream component in the v-Abl transformation program. To explore the mechanism by which v-Abl activates c-myc transcription, a cotransfection assay was developed. We show that transactivation of a c-myc promoter by v-Abl requires the SH1 (tyrosine kinase) and SH2 domains of v-Abl; the C-terminal domains are not required for transactivation. The assay also identified the E2F site in the c-myc promoter as a v-Abl-responsive element. In addition, multimerized E2F sites were shown to be sufficient to confer v-Abl-dependent activation on a minimal promoter. This is the first identification of a v-Abl response element for transcriptional activation. v-Abl tyrosine kinase-dependent changes in proteins binding the c-myc E2F site were also demonstrated, including induction of a complex containing DP1, p107, cyclin A, and cdk2. Identification of v-Abl-dependent changes in E2F-binding proteins provides an important link between v-Abl, transcription, cell cycle regulation, and control of cellular growth.

Neurodegeneration mediated by glutamate and beta-amyloid peptide: a comparison and possible interaction

In Alzheimer's disease, abnormal extracellular accumulations of beta-amyloid (a major component of the senile plaques) and of the excitatory amino acid glutamate are both thought to be associated with degeneration of nerve cells. In the present study, using cultured cortical or hippocampal neurons as an in vitro model, we compared the effects of various factors influencing neurodegeneration mediated by glutamate or by beta-amyloid peptide (A beta). We also asked the question: does long-term treatment with sublethal doses of A beta-(25-35) potentiate glutamate-mediated excitotoxicity? Neuronal cell death was quantified using the lactate dehydrogenase (LDH) method. Since extracellular LDH remains stable for days, the magnitude of relative afflux of LDH correlates in a linear fashion with the number of damaged neurons in cultures. When applied singly, both glutamate (for 15 min) and A beta-(25-35) or its parent peptide A beta-(1-40) (continuously) produced a dose-dependent neuronal degeneration. In the case of glutamate, the half-maximal effects were observed at about 0.08 mM glutamate for both cerebral cortical and hippocampal neurons (cultured for 13 days in vitro, DIV). The effect of A beta-(25-35) was also time-dependent, while neurons grown in a chemically defined medium showed relatively greater susceptibility to A beta-(25-35) than those cultured in a serum-containing medium. These differential effects were not related to the presence of different numbers of glial cells in the cultures. Treatment with different doses of the antimitotic inhibitor, cytosine arabinoside, for 24 h (6-7 DIV) produced at 13 DIV cortical neuronal cultures with varying numbers of astrocytes, as determined by the astrocyte-specific enzyme glutamine synthetase. The presence of astrocytes decreased the toxicity of glutamate for neurons. The modulation was due to uptake of glutamate by astrocytes, thereby reducing its effective concentration, as the effect was seen at 0.1 mM and not at 10 mM glutamate. Incorporation of an NMDA receptor mediated Ca2+ ion channel blocker, MK-801, together with glutamate completely inhibited degeneration of cortical neurons, and pretreatment of cultures with basic fibroblast growth factor for 2 days did so partially. However, these compounds had no effect on neurotoxicity mediated by A beta-(25-35). Lastly, the effect of glutamate interacted with that of A beta-(25-35). Pretreatment of cortical neurons for 2 days with 10 microM A beta-(25-35) by itself had no appreciable effect, but it potentiated significantly the degeneration of these neurons mediated by glutamate.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of protein kinase C modulation on NMDA receptor mediated regulation of neurotransmitter enzyme and c-fos protein in cultured neurons

The role of protein kinase C (PKC) in N-methyl-D-aspartate (NMDA) receptor-mediated biochemical differentiation and c-fos protein expression was investigated in cultured cerebellar granule neurons. The biochemical differentiation of glutamatergic granule cells was studied in terms of the specific activity of phosphate-activated glutaminase, an enzyme treatment in the synthesis of the putative neurotransmitter pool of glutamate. When the partially depolarized cells were treated with NMDA for the last 1 to 3 days (between 2 and 5 days in vitro), it elevated the specific activity of glutaminase. In contrast, NMDA had little effect on the activity of aspartate aminotransferase or of lactate dehydrogenase. Treatment of 10-day old granule neurons with NMDA also resulted in a marked increase in the immunocytochemically measured expression of c-fos protein. The increases in both the activity of glutaminase and the steady state level of c-fos protein were specific to the activation of NMDA receptors, as they were completely blocked by D,L-2-amino-5-phosphonovaleric acid. The specific stimulation of NMDA receptors in PKC-depleted granule neurons or in the presence of reasonably specific PKC inhibitors also produced significant elevation in the activity of glutaminase and the expression of c-fos protein. These increases were similar in magnitude to those observed in the granule neurons of the respective control groups. Our findings demonstrate that PKC is not directly involved in the NMDA receptor-mediated signal transduction processes associated with biochemical differentiation and c-fos induction in cerebellar granule neurons.

MAZ-dependent termination between closely spaced human complement genes

The zinc finger protein MAZ, originally identified as a factor that binds to the c-myc P2 promoter, is associated with transcriptional termination. As shown in these studies, a termination sequence between the closely spaced human complement genes C2 and Factor B contains a protein binding site which interacts with three different proteins in vitro. Binding of one of these factors, MAZ, correlates with activity of the C2 termination sequence in vivo. Cloned MAZ was used to obtain a consensus binding site, G5AG5. This allowed identification of new sites, between the closely spaced human genes g11 and C4 and within an intron of the mouse IgM-D gene, where termination is known to occur and regulate the expression of IgD. The g11 and IgM MAZ sites lie within sequences that have activity in a termination assay and, furthermore, mutation of C2 or g11 MAZ sites severely reduces termination activity. MAZ bends DNA, and inherently bent DNA is highly active as a terminator, suggesting that MAZ-induced bending is important for C2 and g11 termination. We propose that MAZ sites exist in promoters which require protection against transcriptional interference, such as those of closely spaced genes, to cause efficient termination. The MAZ consensus sequence will facilitate the identification of further sites.

A low-affinity nerve growth factor receptor antibody is internalized and retrogradely transported selectively into cholinergic neurons of the rat basal forebrain

The mechanism by which nerve growth factor transduces its signal in responsive cells is yet to be clearly defined. However, it has been suggested that the internalization of nerve growth factor, the first step in the retrograde flow of nerve growth factor, is a property of the high-affinity receptors, p140trkA. Here we show that when a monoclonal antibody (MC 192), which immunoprecipitates p75NGFR (the low-affinity 75,000 mol. wt nerve growth factor receptor protein) and not p140trkA, was administered into the dorsal hippocampal formation of the rats, it was internalized and retrogradely transported to the cell bodies residing in the medial septum-diagonal band complex. The topographic organization and the localization of these neurons containing retrogradely transported p75NGFR antibody were strikingly similar to those nerve cells immunostained for choline acetyltransferase in the immediately-adjacent section, indicating that the neurons which contained p75NGFR antibody were cholinergic neurons. A double-label immunocytochemistry confirmed this conclusion. On the other hand, none of the parvalbumin-positive GABAergic neurons contained retrogradely transported p75NGFR antibody. Moreover, in contrast to specific transport of p75NGFR antibody into cholinergic neurons, when wheat germ agglutinin-colloidal gold was injected into the hippocampus at the same levels, it was taken up and retrogradely transported into both choline acetyltransferase-positive cholinergic and parvalbumin-immunoreactive GABAergic neurons in the medial septum-diagonal band complex.