Impedance profiles of peripheral and central neurons

The electrical impedance of trigeminal ganglion cells (in vivo) and hippocampal CA1 neurons (in vitro) of guinea pigs was measured in the frequency range of 5-1250 Hz using intracellular recording techniques with single microelectrodes and computerized methodology. The transfer functions of the electrode and the electrode-neuron system were computed from the ratio of fast Fourier transforms of the output voltage response from the neuron and input current composed of sine waves with rapidly increasing frequency which displaced membrane potential by 2-5 mV. We believe these to be the first measurements of complex impedance and transfer functions in peripheral and central neurons of vertebrates and the first use of such input current functions. The majority of trigeminal ganglion cells did not exhibit electrical behaviour ascribable to a simple resistance-capacitance (RC) circuit but showed a hump at low frequencies (5-250 Hz) in the computed transfer function, probably attributable to resonance. The transfer function in less than 20% of the trigeminal neurons could be fitted approximately to a theoretical transfer function (resistance in series with a parallel RC circuit model) providing values for electrode resistance, effective input resistance, and effective input capacitance. The transfer functions measured in hippocampal CA1 neurons were characterized by a rapid fall-off in the low frequency range (less than 200 Hz). Impedance locus plots approximate the locus corresponding to a series RC circuit in parallel with a parallel RC circuit.     

Sequential Entry of Transforming Markers into Neisseria meningitidis After Chromosome Alignment

The kinetics of appearance of transformants as a function of time of exposure to deoxyribonucleic acid (DNA) was examined in Neisseria meningitidis. Incubation with chloramphenicol for as long as 2 hr, which probably leads to chromosome alignment, resulted in augmentation of the lag period before the appearance of the first transformants. The lag periods thus found were dependent upon the marker tested. This permitted the construction of a time map according to the lag periods observed for individual markers. This map was in general agreement with the chromosome map of the recipient strain as determined by marker frequency analysis. Transformation of recipient cells with chromosomes aligned by growth to the stationary phase showed the same type of increased lag in the appearance of transformants before the logarithmic phase of growth had again been reached. These results support the assumption that the nature of the marker accepted by a recipient cell corresponds to the marker present at the replication point of the chromosome. In the absence of DNA and protein synthesis, the uptake of one marker seems to be successively followed by other markers in a linear order determined by the chromosome of the recipient cell.     

Frequency response model of skeletal muscle and its association with contractile properties of skeletal muscle

The aims of the present study were to develop a mathematical model of the skeletal muscle based on the frequency transfer function, referred to as frequency response model, and to presume the relationship between the model elements and skeletal muscle contractile properties. Twitch force in elbow flexion was elicited by applying a single electrical stimulation to the motor point of biceps brachii muscles, and then analyzed visually by the Bode gain and phase diagram of the force signal. The frequency response model was represented by a frequency transfer function consisting of five basic control elements (proportional element, dead time element, and three first-order lag elements). The model element constants were estimated by best-fitting to the Bode gain and phase diagram of the twitch force signal. The proportional constant and the dead time in the frequency response model correlated significantly with the peak torque and the latency in the actual twitch force, respectively. In addition, the time constants of the three first-order lag elements in the model correlated strongly with the contraction time and the half relaxation time in the actual twitch force. The results suggested a possibility that the individual elements in the frequency response model would reflect the biochemical and biomechanical properties in the excitation–contraction coupling process of skeletal muscle.     

Kinetic aspects of the aggregation of Clostridium perfringens theta-toxin on erythrocyte membranes. A fluorescence energy transfer study

Fluorescence resonance energy transfer was used to monitor aggregation kinetics of the "thiol-activated" cytolysin (perfringolysin O (PFO) or theta-toxin) of Clostridium perfringens on erythrocyte membranes. PFO was labeled with the isothiocyanate derivatives of either fluorescein or tetramethylrhodamine. No detectable change in the hemolytic activity of PFO was detected after modification with either fluorophore at a ratio of 1:2 fluorophore molecules/cytolysin molecule. Fluorescence energy transfer (FET) between the donor (fluorescein.PFO or PFOD) and the acceptor (tetramethylrhodamine.PFO or PFOA) was detected by both quenching of donor fluorescence (520 nm) and by enhancement of acceptor fluorescence (575 nm) upon aggregation of labeled cytolysin molecules. FET was only observed when PFOD and PFOA were incubated in the presence of membranes. FET was not observed when PFOD and PFOA were incubated in a membrane-free solution or when unlabeled toxin was substituted for PFOA. FET was also found to be temperature-dependent. The temperature-dependent rates of change in FET upon mixing labeled toxin with erythrocyte membranes proceeded without a lag phase and displayed an activation energy of 18.7 kcal/mol. At all temperatures aggregation of PFO was virtually complete before the onset of hemolysis, the latter exhibiting a distinct lag phase. The lag period before onset of hemolysis was temperature-dependent and exhibited an activation energy of 23.2 kcal/mol. These results suggest that the aggregation of membrane-associated PFO is necessary to initiate the hemolytic process, and the lag phase which occurs before onset of hemolysis reflects the kinetics of PFO monomer to polymer conversion.     

Effects of pulse ultrasonic irradiation on the lag phase of Saccharomyces cerevisiae growth

Aims: This paper presents an analysis of lag phase phenomena in Saccharomyces cerevisiae growth as a function of ultrasonic irradiation. Methods and Results: Pulse irradiation treatments were performed by a 20 kHz ultrasonic transducer with different durations and energies. Data obtained from experiments were then employed to estimate growth parameters by specific transfer function. The significance of the different lag times in response to ultrasonic irradiation was analysed. The results showed that the yeast growth in lag phase responded to the irradiated ultrasonic of 20 min more than the 10 min. The ultrasonic energies between 330 and 360 W s m^?3 could decrease lag time up to 1 h compared to the sample without ultrasonic irradiation. Conversely, the treatments with energies higher than 850 W s m^?3 were able to extend the lag time and decrease the yeast growth. Conclusions: The lag durations of S. cerevisiae were changed significantly by different ultrasonic irradiations, energies and durations. In particular, sufficient irradiation energies reduced the lag time, resulting in accelerated yeast growth. In contrast, high energy could inactivate growth by increasing the lag time. Significance and Impact of the Study: This work provides an alternative technique to either accelerate or inactivate the S. cerevisiae lag phase. The approach can be developed in experiment designed to control the yeast growth by ultrasonic irradiation as assistance in the environments.     

Neural network model of on-off units in the fly visual system: simulations of dynamic behavior

We analyze the dynamic properties of a neural network model for on-off spiking neurons recorded in the first optic chiasm of the fly visual system. The model consists of two parallel pathways and three sequential processing stages. The first stage models photoreceptors. At the second stage, the signal is segregated into on- and off-pathways. These pathways are proposed to correspond to two populations of amacrine cells. At the third stage, the on- and off-pathways converge to on-off neurons. Furthermore, according to the model, on-off neurons interact via recurrent connections. This stage is proposed to correspond to lamina L4 neurons. In response to luminance increments and decrements, the model exhibits a three-component response and suggests pathways for each of the components. When stimulated by a train of pulses, the model exhibits fast adaptation for frequencies higher than about 5 Hz. Furthermore, adaptation to on- and off-pulses occurs independently. When the frequency of stimulation is reduced, the unit recovers rapidly from its adapted state. The temporal modulation transfer function has its peak around 7 Hz. The phase characteristics show a phase lead for low temporal frequencies changing to a phase lag for high frequencies. These model predictions are compared with data from Jansonius and van Hateren (1991). Received: 26 May 1997 / Accepted in revised form: 19 February 1998     

Energy-dependent intracellular translocation of proparathormone

We previously suggested that after synthesis, proparathormone is transferred from rough endoplasmic reticulum to the Golgi region where its conversion to parathormone occurs. We have attempted to define more closely this transfer process. In the first type of study, bovine parathyroid slices were incubated with [3H]leucine for 10 min and then radioisotope labeling was restricted by addition of a large excess of nonradioactive leucine. Under these conditions, more than 90% of the initially labeled proparathormone was converted to parathormone in 40 min. Lowered temperature in the chase period markedly inhibited the conversion. Several chemical agents were employed individually in the chase period to examine their effect on the conversion process. Antimycin A, dinitrophenol, oligomycin, and anaerobiosis (N2) inhibited the conversion, whereas sodium flouride and cycloheximide had no effect. In the second type of study, parathyroid slices were incubated with [3H]leucine for the entire incubation period. Lowered temperature and inhibitors of energy metabolism and microtubular function all lengthened the interval (lag) between the initial synthesis of [3H]parathormone. Cycloheximide, Tris, and chloroquine decreased the rates of protein synthesis and conversion, respectively, but none had any effect on the lag. We interpret the lag to represent the time of transit for proparathormone from rough endoplasmic reticulum to the Golgi region. We conclude that this transfer process is independent of the synthesis of the prohormone and its conversion to the hormone. Moreover, this translocation requires metabolic energy and appears to be mediated by microtubules.     

Lag phase of CO2-dependent O2 evolution by illuminated Anabaena variabilis cells.

The steady-state rate of CO2-dependent O2 evolution by Anabaena variabilis cells in response to illumination was established after a lag phase. The lag phase was shortened (1) in cells incubated with glucose as an oxidizable substrate and (2) upon an increase in light intensity. The lag phase was absent during electron transfer from H2O to p-benzoquinone (in combination with ferricyanide) involving Photosystem II. A lag was observed during electron transfer from H2O to methyl viologen involving Photosystems II and I, but not for electron transfer from N,N,N',N'-tetramethyl-p-phenylenediamine (in combination with ascorbate) to methyl viologen involving only Photosystem I. The lag phases of the light-induced H2O --> CO2 and H2O --> methyl viologen electron transfer reactions showed the same temperature dependences at 10-30 degrees C. The lag was prevented by 3-(3,4-dichlorophenyl)-1,1-dimethylurea at concentrations that caused partial inhibition of photosynthetic O2 evolution. Retardation of cell respiration by a combination of CN- and benzylhydroxamate shortened the lag phase of the H2O --> methyl viologen electron transfer. It is concluded that the lag phase is associated with the electron transfer step between Photosystem II and Photosystem I common for the photosynthetic and respiratory chains and is due to the stimulation of cell respiration during the initial period of illumination as a consequence of an increase in the reduced plastoquinone pool and to subsequent retardation of respiration resulting from the transition of the electron transfer chain to the competitive pathway involving Photosystem I.     

Neural mechanisms potentially contributing to the intersegmental phase lag in lamprey

Factors contributing to the production of a phase lag along chains of oscillatory networks consisting of Hodgkin-Huxley type neurons are analyzed by means of simulations. Simplified network configurations are explored consisting of the basic building blocks of the spinal central pattern generator (CPG) generating swimming in the lamprey. It consists of reciprocally coupled crossed inhibitory C interneurons and ipsilateral excitatory E interneurons that activate C neurons and other E neurons. Oscillatory activity in the model network can, in the simplest case, be produced by a pair of reciprocally coupled C interneurons oscillating through an escape mechanism. Different levels of tonic excitation drive the network over a wide burst frequency range. In this type of network, powerful frequency-regulating factors are the effective inhibition produced by the active side, in combination with the tendency of the inactive side to escape from the inhibition. These two mechanisms can be affected by several factors, e.g. spike frequency adaptation (calcium-dependent K(+) channels), N-methyl-D-aspartate membrane properties as well as presence of low-voltage activated calcium channels. A rostrocaudal phase lag can be produced either by extending the contralateral inhibitory projections or the ipsilateral excitatory projections relatively more in the caudal than the rostral direction, since both an increased inhibition and a phasic excitation slow down the receiving network. The phase lag becomes decreased if the length of the intersegmental projections is increased or if the projections are extended symmetrically in both the rostral and the caudal directions. The simulations indicate that the conditions in the ends of an oscillator chain may significantly affect sign, magnitude and constancy of the phase lag. Also, with short and relatively weak intersegmental connections, the network remains robust against perturbations as well as intrinsic frequency differences along the chain. The phase lag (percentage of cycle duration) increases, however, with burst frequency also when the coupling strength is comparatively weak. The results are discussed and compared with previous "phase pulling" models as well as relaxation oscillators.     

Stopped-flow analyses on the reaction of ascorbate with cytochrome b561 purified from bovine chromaffin vesicle membranes

Cytochrome b(561) in adrenal chromaffin vesicle membranes conveys electron equivalents from extravesicular ascorbate to the intravesicular monodehydroascorbate radical. We conducted a stopped-flow study on the reaction of ascorbate with purified cytochrome b(561) in the detergent-solubilized state for the first time. The time course of the reduction of oxidized cytochrome b(561) with ascorbate could not be fitted with a single exponential but with a linear combination of at least four exponential functions. This result is consistent with the notion that cytochrome b(561) contains two hemes b, each having a distinct redox potential and a function upon reactions with ascorbate and monodehydroascorbate radical. The fastest phase, which was assigned to the first one-electron donation from ascorbate to heme b on the extravesicular side, was further analyzed by transient phase kinetics employing a two-step bi-uni sequential ordered mechanism. The result showed K(s) = 2.2 mM for ascorbate at pH6.0. At a region below pH5.5, there was a significant lag before the reduction of hemes b occurred. This time lag was interpreted as due to a pH-dependent transient state before the first electron transfer to take place. The fastest phase was completely lost by N-carbethoxylation of heme-coordinating histidyl residues (His88 and His161) and Lys85 upon treatment with diethylpyrocarbonate. The presence of ascorbate during the treatment inhibited the N-carbethoxylation of the histidyl residues and, thereby, restored the final reduction level of hemes b. But the reduction rate was still only one-twentieth of the native form. This result suggested an important role of the conserved Lys85 for the interaction with ascorbate.     

Exercise training augments the dynamic heart rate response to vagal but not sympathetic stimulation in rats

We examined the transfer function of autonomic heart rate (HR) control in anesthetized sedentary and exercise-trained (16 wk, treadmill for 1 h, 5 times/wk at 15 m/min and 15-degree grade) rats for comparison to HR variability assessed in the conscious resting state. The transfer function from sympathetic stimulation to HR response was similar between groups (gain, 4.2 ± 1.5 vs. 4.5 ± 1.5 beats·min(-1)·Hz(-1); natural frequency, 0.07 ± 0.01 vs. 0.08 ± 0.01 Hz; damping coefficient, 1.96 ± 0.55 vs. 1.69 ± 0.15; and lag time, 0.7 ± 0.1 vs. 0.6 ± 0.1 s; sedentary vs. exercise trained, respectively, means ± SD). The transfer gain from vagal stimulation to HR response was 6.1 ± 3.0 in the sedentary and 9.7 ± 5.1 beats·min(-1)·Hz(-1) in the exercise-trained group (P = 0.06). The corner frequency (0.11 ± 0.05 vs. 0.17 ± 0.09 Hz) and lag time (0.1 ± 0.1 vs. 0.2 ± 0.1 s) did not differ between groups. When the sympathetic transfer gain was averaged for very-low-frequency and low-frequency bands, no significant group effect was observed. In contrast, when the vagal transfer gain was averaged for very-low-frequency, low-frequency, and high-frequency bands, exercise training produced a significant group effect (P < 0.05 by two-way, repeated-measures ANOVA). These findings suggest that, in the frequency domain, exercise training augments the dynamic HR response to vagal stimulation but not sympathetic stimulation, regardless of the frequency bands.     

On the interaction between heparin and some aminoglycoside antibiotics

An interaction between the aminoglycoside antibiotics and heparin wherein charge transfer complexes are formed has been investigated to determine the degree of inhibition of antibacterial function of the antibiotic in the complexed form.Minimum inhibitory concentration (MIC) values have been obtained for the action of the aminoclycoside antibiotics tobramycin, gentamicin, amikacin, kanamycin, and streptomycin, on a sensitive strain ofE. coli. Growth curves ofE. coli determined at concentrations of these antibiotics just below the MIC demonstrated significant lengthening of the lag phase relative to control growth curves generated in the absence of antibiotic. Heparin (1 U ml^–1 and 10 U ml^–1) had no effect on control growth curves; however, particularly at the higher concentration, it reduced the effect on the lag phase produced by the aminoglycoside antibiotics. Thus kanamycin, gentamicin, and tobramycin were most affected, while amikacin and streptomycin were least affected. The rank order of inhibition of antibiotic activity by interaction with heparin was in qualitative agreement with previously published figures for the degree of complexation between antibiotics and heparin.     

Transfer characteristic of the motor system of the hand obtained by electrical stimulation and its bearing on force tremor (author's transl)]

Pulse duration modulated signals were used to stimulate the extensor muscles of the hand. From this and from the isometric tension responses the frequency response of the human motor system was obtained. From the transfer characteristics of the components of the motor system which were taken from literature the frequency response of a closed-loop circuit model could be calculated. The theoretical frequency response was compared to the observed data. With increasing loop gain the model would show the characteristics of a filter tuned to the frequency of force-tremors.     

Initiation of glycogen biosynthesis in Escherichia coli. Studies of the properties of the enzymes involved.

The properties of the enzymes involved in the initiation of glycogen biosynthesis in Escherichia coli were studied. It was found that the enzymic activities which transfer the glycosyl residues from UDPglucose or ADPglucose for the glucoprotein synthesis had differing stabilities upon storage at 4 degrees C. The small amount of glycogen and the saccharide firmly bound to the membrane preparation, were degraded during the storage period. The activity measured in fresh and in stored preparations gave different time dependence curves. The stored preparation had a lag period which could be due to the transfer of the first glucose units to the protein. Both UDPglucose and ADPglucose : protein glucosyltransferases were affected in different ways by detergents. Based on the results presented, it may be concluded that both enzymatic activities are due to different enzymes. Furthermore, both enzymatic activities are different from that which transfers glucose from ADPglucose to glycogen. The following mechanism for the de novo synthesis is suggested. Glycogen in E. coli could be initiated by two different enzymes which transfer glucose to a protein acceptor either from UDPglucose or ADPglucose. Once the saccharide linked to the protein has reached a certain size it is almost exclusively enlarged by another ADPglucose-dependent enzyme. The participation of branching enzyme will produce a polysaccharide with the characteristics of glycogen.     

Functional significance of the statistical properties of the retinal discharge

Summary In this paper the effect of the statistical properties of the ganglion cell discharge on the transfer characteristics of the cat's retinal sensory system is studied. On the basis of results reported by the literature, a mathematical model of the system is defined. The model is then studied by digital computer, to obtain the amplitude of its response to sinusoidal stimulation as a function of frequency. The results show that, as the discharge is not Poisson-like, a positive resonance exists between stimulus and discharge at stimulus frequencies whose period is of the same order as, or smaller than the mean interval of the discharge. The amplitude of the resonance is a function of the statistical parameters of the discharge. These results fit well experiments recently carried out.     

Influence of Auxin on Young's Modulus in Stems and Roots of Pisum and the Theory of Changing the Modulus in Tissues

The effect of auxin on elastic extensibility has been investigated by means of the resonance frequency melhod in Pisum, sativum. The time lag for the decrease in Young's modulus E, caused by IAA, was between 2 and 3 minutes in etiolated stem internodes. The time lag for growth was about 7 minutes. The measurements of E in root segments were only qualitative owing to the structural characteristics; IAA decreases E in roots as it does in stems, but only in the region where IAA is assumed to enhance elongation. The connexion between elastic modulus and growth is discussed with reference to other investigations. The assumption has been made that a decrease in elastic modulus indicates a change in the cell wall which in some way is conducive to growth (induction of elongation). The theoretical possibilities of changing E have been discussed with reference to the formula for water fluxes. Both a change in a cell wall properly and a change in the cytoplasmic permeability are able to cause a change in E in the same way as auxin does. An early action of auxin must be located in the cell-wall-plasmalemma region.     

Ultrasound interaction with large unilamellar vesicles at the phospholipid phase transition: perturbation by phospholipid side chain substitution with deuterium

The ultrasonic absorption, alpha lambda, as a function of temperature and frequency was determined in large unilamellar vesicles (LUVs) in which specific phospholipid side chains were deuterated. Deuteration significantly altered the temperature and frequency dependence of alpha lambda. The frequency change was especially marked, with decreased frequency and broadening of the ultrasound relaxation, even with only minor changes in the phase transition temperature. Deuteration decreased the Tm and enthalpy of the lipid phase transition, as shown by differential scanning calorimetry, whereas electron spin resonance showed that at and above the lipid phase transition, no differences in the mobility as a function of temperature were observed. These results show that the observed increase in ultrasonic absorption in LUVs at the phospholipid phase transition arises from the interaction of ultrasound with the hydrophobic side chains, probably coupling with structural reorganization of small domains of molecules, a process which is maximized at the phase transition temperature.     

Initiation of glycogen biosynthesis in Escherichia coli studies of the properties of the enzymes involved

The properties of the enzymes involved in the initiation of glycogen biosynthesis in Escherichia coli were studied.It was found that the enzymic activities which transfer the glycosyl residues from UDPglucose or ADPglucose for the glucoprotein synthesis had differing stabilities upon storage at 4°C.The small amount of glycogen and the saccharide firmly bound to the membrane preparation, were degraded during the storage period.The activity measured in fresh and in stored preparations gave different time dependence curves. The stored preparation had a lag period which could be due to the transfer of the first glucose units to the protein.Both UDPglucose and ADPglucose: protein glucosyltransferases were affected in different ways by detergents.Based on the results presented, it may be concluded that both enzymatic activities are due to different enzymes. Furthermore, both enzymatic activities are different from that which transfers glucose from ADPglucose to glycogen.The following mechanism for the de novo synthesis is suggested. Glycogen in E. coli could be initiated by two different enzymes which transfer glucose to a protein acceptor either from UDPglucose or ADPglucose. Once the saccharide linked to the protein has reached a certain size it is almost exclusively enlarged by another ADPglucose-dependent enzyme. The participation of branching enzyme will produce a polysaccharide with the characteristics of glycogen.     

Dynamic behavior of small heat shock protein inhibition on amyloid fibrillization of a small peptide (SSTSAA) from RNase A

Small heat shock proteins, a class of molecular chaperones, are reported to inhibit amyloid fibril formation in vitro, while the mechanism of inhibition remains unknown. In the present study, we investigated the mechanism by which Mj HSP16.5 inhibits amyloid fibril formation of a small peptide (SSTSAA) from RNase A. A model peptide (dansyl-SSTSAA-W) was designed by introducing a pair of fluorescence resonance energy transfer (FRET) probes into the peptide, allowing for the monitoring of fibril formation by this experimental model. Mj HSP16.5 completely inhibited fibril formation of the model peptide at a molar ratio of 1:120. The dynamic process of fibril formation, revealed by FRET, circular dichroism, and electron microscopy, showed a lag phase of about 2 h followed by a fast growth period. The effect of Mj HSP16.5 on amyloid fibril formation was investigated by adding it into the incubation solution during different growth phases. Adding Mj HSP16.5 to the incubating peptide before or during the lag phase completely inhibited fibril formation. However, introducing Mj HSP16.5 after the lag phase only slowed down the fibril formation process by adhering to the already formed fibrils. These findings provide insight into the inhibitory roles of small heat shock proteins on amyloid fibril formation at the molecular level.