Blockade by ifenprodil of high voltage-activated Ca2+ channels in rat and mouse cultured hippocampal pyramidal neurones: comparison with N-methyl-D-aspartate receptor antagonist actions

1. The block by ifenprodil of voltage-activated Ca2+ channels was investigated in intracellular free calcium concentration ([Ca2+]i) evoked by 50 mM K+ (high-[K+]o) in Fura-2-loaded rat hippocampal pyramidal neurones in culture and on currents carried by Ba2+ ions (IBa) through Ca2+ channels in mouse cultured hippocampal neurones under whole-cell voltage-clamp. The effects of ifenprodil on voltage-activated Ca2+ channels were compared with its antagonist actions on N-methyl-D-aspartate- (NMDA) evoked responses in the same neuronal preparations. 2. Rises in [Ca2+]i evoked by transient exposure to high-[K+]o in our preparation of rat cultured hippocampal pyramidal neurones are mediated predominantly by Ca2+ flux through nifedipine-sensitive Ca2+ channels, with smaller contributions from nifedipine-resistant, omega-conotoxin GVIA-sensitive Ca2+ channels and Ca2+ channels sensitive to crude funnel-web spider venom (Church et al., 1994). Ifenprodil (0.1-200 microM) reversibly attenuated high-[K+]o-evoked rises in [Ca2+]i with an IC50 value of 17 +/- 3 microM, compared with an IC50 value of 0.7 +/- 0.1 microM for the reduction of rises in [Ca2+]i evoked by 20 microM NMDA. Tested in the presence of nifedipine 10 microM, ifenprodil (1-50 microM) produced a concentration-dependent reduction of the dihydropyridine-resistant high-[K+]o-evoked rise in [Ca2+]i with an IC50 value of 13 +/- 4 microM. The results suggest that ifenprodil blocks Ca2+ flux through multiple subtypes of high voltage-activated Ca2+ channels. 3. Application of the polyamine, spermine (0.25-5 mM), produced a concentration-dependent reduction of rises in [Ca2+]i evoked by high-[K+]o. The antagonist effects of ifenprodil 20 micro M on high-[K+]0-evoked rises in [Ca2+]. were attenuated by spermine 0.25 mM but not by putrescine 1 or 5 mM. In contrast,spermine 0.1 mM increased rises in [Ca2+]i evoked by NMDA and enhanced the ifenprodil (5 micro M) block of NMDA-evoked rises in [Ca2+]i.4. Similar results were obtained in mouse cultured hippocampal pyramidal neurones under whole-cell voltage-clamp. Ifenprodil attenuated both the peak and delayed whole-cell IB. with an IC% value of 18 +/- 2 micro M, whilst it attenuated steady-state NMDA-evoked currents with an IC50 of 0.8 +/- 0.2 micro M. Block of IBa by ifenprodil 10 JaM was rapid in onset, fully reversible and occurred without change in thecurrent-voltage characteristics of Ba. The ifenprodil block of IBa was enhanced on membrane depolarization and was weakly dependent on the frequency of current activation. Spermine 0.1 mM potentiated control NMDA-evoked currents but attenuated IB,. In agreement with the microspectrofluorimetric studies, co-application of spermine produced a small enhancement of the inhibitory effect of ifenprodil 10 micro M on NMDA-evoked responses whereas the reduction of I4 by ifenprodil 10 micro M in the presence of spermine was less than expected if the inhibitory effects of ifenprodil and spermine on IBa were simply additive.5. The results indicate that ifenprodil blocks high voltage-activated Ca2+ channels in rat and mouse cultured hippocampal pyramidal neurones. Although the Ca2+ channel blocking actions of ifenprodil are observed at higher concentrations than those associated with NMDA antagonist activity, Ca2+ channel blockade may contribute, at least in part, to the established neuroprotective and anticonvulsant properties of the compound.     

Increased absolute light sensitivity in Himalayan mice with cold-induced ocular pigmentation

Controversy over the relationship between ocular pigmentation and absolute dark-adapted light sensitivity has persisted for over two decades. Previous electrophysiological experiments in hypopigmented mammals (mice, rats, rabbits) show increased thresholds in the dark-adapted state proportional to the deficit in ocular melanin. Animals with the least amount of ocular melanin have the most elevated thresholds. Dark-adapted thresholds in hypopigmented mice show similar threshold elevations in behavioral tests. The present study extends these findings to show that a specific increase in ocular pigmentation results in the converse effect, lowered absolute dark-adapted thresholds. The increase in ocular melanin was accomplished by keeping Himalayan mice in the cold (4 degrees C) for 6 weeks. Himalayan mice (C57BL/6J cH/cH) were compared to black mice (C57BL/6J (+/+)) and albino mice (C57BL/6J c2J/c2J) after 6 weeks at either 4 degrees C or 20 degrees C in 12-h cycling light (<1 cd/m2). The Himalayan mice that were kept in the cold exhibited a 44% increase in ocular melanin compared to Himalayan mice kept at room temperature. Cold rearing did not effect ocular melanin or visual thresholds in control animals (black mice = 10(-5.9) cd/m2 and albino mice = 10(-4.4) cd/m2). In contrast, the Himalayan mice maintained at 4 degrees C had thresholds of 10(-5.7) cd/m2 compared to 10(-5.1) cd/m2 for Himalayan mice kept at 20 degrees C. This represents compelling evidence of a direct relationship between ocular melanin concentration and absolute dark-adapted light sensitivity.     

Isothermal solidification kinetics of diffusion brazing

Diffusion brazing (DB) is a process that produces interface-free joints that approach the bulk properties of the material that is to be joined. Solid-state diffusion of the melting point depressant (MPD) element into the joint metal causes the solid/liquid (S/L) interface to advance until the joint is solidified. The time required to complete this isothermal solidification stage was modeled using a moving boundary analysis. Precision measurements of the interlayer width as a function of time were made on the copper-silver system. The bonding apparatus consisted of a suspended load feedback system that prevented leakage of joint metal due to extrusion or surface wetting, thus preserving mass balance. The interlayer width vs bonding time measurements obtained were found to be within a factor of 4 of the theoretical model. The difference was ascribed to the difficulty in accurately measuring the actual liquid width and loss of silver due to vaporization. Large spherical protrusions grow during bonding, which further roughens the interface. However, experimental and predicted concentration profiles of silver were found to be in complete agreement. As the liquid remaining in the grain boundary grooves is diffused away, porosity can develop due to volume changes. By holding the joint at temperature for extended periods, complete solidification followed by homogenization will occur. Selecting the appropriate bonding temperature to achieve a specified maximum concentration of braze metal at the joint is dependent on both the isothermal solidification and homogenization kinetics.     

Fabrication of submicron high-aspect-ratio GaAs actuators

Submicron, single-crystal gallium arsenide (SC-GaAs) actuators have been designed, fabricated, and operated. The fabrication process, called SCREAM-II (single crystal reactive etching and metallization II), uses chemically assisted ion beam etching (CAIBE) and reactive ion etching (RIE) to produce suspended and movable SC-GaAs structures with up to a 25:1 aspect ratio of vertical depth (10 μm) to lateral width (400 nm). Integrated actuators with predominantly vertical sidewall (PVS) aluminum electrodes are used to move the structures. Silicon nitride is used as an etch mask, structural stiffener, and electrical insulator. An x-y stage with integrated actuators produces controllable x-y displacements of ±1.8 μm when a voltage of 54.5 V is applied to either or both of the x and y actuators. The x-y stage resonates for an applied sinewave of 20 V (peak to peak) with f=10.5 kHz and a DC offset of 10 V. The structural vibration amplitude is 0.6 μm     

Advanced colorectal cancer is associated with impaired interleukin 12 and enhanced interleukin 10 production

Interleukin 12 (IL-12) is a heterodimeric cytokine that has been demonstrated to have a major role in stimulating a cell-mediated antitumor response. IL-10, a product of T helper 2 lymphocytes, is its most potent inhibitor. The aim of this study was to investigate whether patients with colorectal cancer had an imbalance in production of IL-12 and IL-10 preoperatively, and whether this was associated with advanced disease at surgery. Blood was obtained before surgery from 60 patients with colorectal cancer and from 30 controls. Peripheral blood mononuclear cells were incubated with Staphylococcus aureus Cowan's strain 1 in vitro for 24 h to assess IL-12 expression after stimulation, and serum was used for IL-10 measurement. IL-12 and IL-10 levels were assessed by ELISA. A single pathologist staged the tumors according to the tumor-node-metastasis (TNM) and Dukes' classifications. Patients with colorectal cancer had significantly lower levels of IL-12 (P <0.001) and higher levels of IL-10(P = 0.004) compared to controls. In addition, lower levels of IL-12 were detected in those patients who were node positive (P<0.05), had Dukes' C lesions (P < or = 0.001), and T3 or T4 lesions (P<0.033) when compared to controls. Patients with Dukes' B and C lesions (P<0.01) and T3 and T4 lesions (P<0.05) also had higher levels of IL-10 compared to controls. This study is the first to demonstrate that patients with colorectal cancer have decreased IL-12 production and increased serum IL-10. This suggests an impaired T helper 1 cell-mediated antitumor response and provides some justification for exogenous IL-12 therapy or anti-IL-10 therapy in these patients.     

Estimates of glycolysis, pyruvate (de)carboxylation, pentose phosphate pathway, and methyl succinate metabolism in incapacitated pancreatic islets

Pancreatic islets were cultured for 24 h in the presence of 1 mM glucose, which renders islets incapable of responding to glucose with insulin release. These islets were compared to islets maintained at 20 mM glucose for 24 h. Detritiation of [2-3H]glucose and [5-3H]glucose in 1 mM glucose islets was normal, suggesting that glucose transport and phosphorylation and all enzymes of glycolysis were not down-regulated in the incapacitated islets. 14CO2 formation from [U-14C]glucose and [6-14C]glucose was inhibited up to 80% and 14CO2 from methyl succinate was inhibited up to 60%, indicating that down-regulation at (a) mitochondrial site(s) might explain the incapacitated insulin release. 14CO2 formation from [3,4-14C]glucose (which becomes [1-14C]pyruvate) was decreased, indicating that the reaction catalyzed by pyruvate dehydrogenase was down-regulated. This decrease, however, was not as large as the decreases in 14CO2 formation from [U-14C]glucose, [2-14C]glucose (which becomes [2-14C]pyruvate), or [6-14C]glucose (which becomes [3-14C]pyruvate), indicating that other reactions were also down-regulated. 14CO2 formation from [1-14C]glucose was inhibited less than that from [6-14C]glucose in the incapacitated islets (34 vs 54%) and these rates indicated that flux of glucose through the pentose phosphate pathway was increased in the incapacitated islet, such that 29% (0.4 nmol of 1.4 glucose/100 islets/90 min) was metabolized via this pathway in the incapacitated islet but only 3.4% (0.1 of 2.9 nmol glucose/100 islets/90 min) was metabolized via the pentose pathway in the 20 mM glucose islets. With rates of 14CO2 evolved from glucose labeled at C2 and C6 and from methyl succinate labeled at C1 + C4 and C2 + C3 the 14CO2 ratio formula was used to calculate the ratios of carboxylated and decarboxylated pyruvate. Roughly equal amounts of pyruvate entered the citric acid cycle by each route in islets maintained for 24 h at 1, 5, or 20 mM glucose. The results indicate that decarboxylation and carboxylation of pyruvate were about equally suppressed in incapacitated islets and that direct inhibition of reactions of the cycle was unlikely. This is consistent with evidence which indicates that down-regulation of both pyruvate carboxylase and pyruvate dehydrogenase occurs in incapacitated islets, i.e., under long-term conditions that modify amounts of enzymes (MacDonald et al., 1991, J. Biol. Chem. 266, 22392-22397).(ABSTRACT TRUNCATED AT 400 WORDS)     

Some Statistical Properties of the Visual Evoked Potential in Man and Their Application as a Criterion of Normality

The average visual evoked potential in man is found to be characterized by six major potential waves or deflections. A computer-aided visual inspection technique is used to extract and measure the 12 parameters corresponding to the amplitude and latency of the six peaks from the responses of 50 subjects. It is then demonstrated that each of these parameters is approximately individually Gaussian distributed and their means and variances are found. With this information, a simple statistical model for the normal visual evoked potential is constructed. It is next assumed that the same 12 parameters are jointly Gaussian distributed and the correlation matrix is computed. A principal components analysis is then applied to this matrix and it is found that the 12 correlated visual evoked potential parameters can be transformed into a reduced set of four uncorrelated components accounting for approximately 76 percent of the total variance of the original set. The four components are then rotated using a varimax technique and the correlation between these components and the original 12 parameters is found to reveal some interesting aspects of the visual evoked potential (VEP) pattern behavior.     

Prediction of corrosion product stability in high-temperature aqueous systems

Calculated thermodynamic data for metal oxidation/oxide reduction reactions of Fe, Ni, Co and Cu, and for formation, oxidation and reduction of NiFe₂O₄, CoFe₂O₄, CuFeO₂ and CuFe₂O₄, are examined for aqueous systems containing dissolved hydrogen and oxygen at temperatures up to 300°C. The data are presented as equilibrium partial pressures of oxygen and hydrogen for specific reactions. This information is used to predict which solids are stable in an equilibrium system containing known concentrations of oxygen and hydrogen, and in a non-equilibrium system in which γ and neutron radiation fields cause the concentrations of oxygen and hydrogen to be much greater than the equilibrium values. Results of X-ray diffraction studies of corrosion products filtered from the heat-transport system of the Douglas Point Generating Station are compared with phase stability predictions.