Inactivation of voltage-dependent calcium current in an insulinoma cell line

We have studied the mechanism of Ca current inactivation in the -cell line HIT-T15 by conventional and perforated patch recording techniques, using two pulse voltage protocols and a combination of current and tail current measurements. In 5 mM Ca, from a holding potential of - 80 mV, the maximum current showed a complex time course of inactivation: a relatively fast, double exponential inactivation (_h1 12 ms and _h2 60 ms) and a very slowly inactivating component ( > 1 s). The faster component (_h1) was due to the voltage-dependent inactivation of a low-threshold-activated (LVA), T-type current, which deactivates more slowly ( 3–5 ms) than the other components ( 0.2–0.3 ms). The intermediate component (_h2) was due to the Ca-dependent inactivation of a portion of the high-threshold-activated (HVA) current. A saturating dose of the dihydropyridine (DHP) nifedipine (10 M) did not affect the LVA current, but inhibited by 68 ± 5% the transient, Ca-sensitive portion of the HVA current and by 33 ± 12% the long lasting component. We suggest that three components of the calcium current can be resolved in HIT cells and the main target of DHPs is a HVA current, which inactivates faster than the DHP-resistant HVA component and does so primarily through calcium influx. Correspondence to: C. Marchetti     

Photocurrent kinetics of purple-membrane sheets bound to planar bilayer membranes

Summary The kinetics of light-driven proton transport by bacteriorhodopsin has been studied in a model system consisting of a planar lipid bilayer membrane to which purple membrane fragments have been attached. After excitation with a 10-nsec laser flash a fast negative current-transient occurs, followed by a positive transient which decays to zero. The time course of the photocurrent may be represented by a sum of four exponentials with time constants ₁= 1.2sec, ₂= 17sec, ₄= 57sec, ₁= 950sec (at 25°C). In a D₂O medium ₂ and ₃ are increased by a factor of 2.6 and 2.9, respectively, whereas ₁ remains unaffected. The observed components of the photocurrent can be correlated to photochemical reaction steps inferred from flash-photometric experiments on the basis of the observed time constants, the activation energies, and the effects of pH and D₂O. From the photocurrent signals information may be obtained on the magnitude of the charge displacement associated with the elementary transitions of the bacteriorhodopsin molecule.     

Sodium channel opening as a precursor to inactivation

The time constant of the process producing the delay in Na inactivation development as determined by the two pulse method (_delay) was extracted and compared to that of the slowest Na activation process ₃ for the I _Na during the conditioning pulse of that same determination. _delay and two pulse inactivation _c values were computer generated using a nonlinear least squares algorithm. _h and single pulse inactivation _h values were independently generated for each determination also with the aid of the computer using the same non-linear least squares algorithm. In one determination at 2 mV, _c was 4.68 and _delay 0.494 ms while _h was 4.70 and ₃ 0.491 ms for a _c/_h of 0.996 and a _delay/₃ of 1.006. Mean _delay/₃ from five determinations in four axons, both Cs and K perfused, and spanning a potential range of-27 to 2mV was 1.068. The precursor process to inactivation is channel opening. Some fraction of channels presumably inactivate via another route where prior channel opening is not required.     

Holling's “hungry mantid” model for the invertebrate functional response considered as a Markov process. Part I: The full model and some of its limits

In this paper we give an analytical reformulation of Holling's (1966) simulation model for invertebrate predatory behaviour. To this end we represent a population of predators as a frequency distribution over a space of (physiological) states. The functional response of a predator is calculated from the (stable) equilibrium distribution of its state as a function of prey density.Starting from the general model various other models are obtained by limit processes, some of them new and some of them old. The more interesting of which will be studied in further papers in this series.List of Notation a rate constant of digestion - b maximum of rate constant of prey encounter in the mantid - b maximum pursuit duration in the mantid (_p(0)) - c satiation threshold for search - c satiation threshold for pursuit in the mantid: c=c(b-D_s/v)/b - D _m maximum sighting distance - D _p pursuit distance - D _s strike distance - expectation operator - f, f ₀ rate of change of satiation during search - f ₁ rate of change of satiation during prey handling - F functional response: number of prey eaten per unit of time by one predator - g rate constant of effective prey encounter in the gobbler and sucker - g₀ rate constant of prey encounter - g₁ probability of no prey loss from pursuit - g₂ probability of no prey escaping during pursuit - H Holling secretary correction factor in the sucker: fraction of the time spent searching - k _R density of R - k_T probability density of maximum prey handling time - K probability that maximum prey handling time is _e, i.e. pursuit duration is zero - K _R distribution function of R - N number of prey caught - p (marginal) density of S - p₀ density of S in search - p₁ simultaneous density of S and T - P probability - p ₁ marginal density of S in handling prey - q probability of strike success - R ratio of realized to maximum sighting distance - s, S satiation - satiation axis - t time - handling time axis - u eating speed - U homogeneous(0,1) random variable - v pursuit speed - V exponential(1) random variable - w prey weight - W exponential(_m) random variable - x prey density - ratio of maximum successful pursuit duration to meal duration (_pm/_e) - _pm - relative duration of successful pursuit (_p/_pm) - ratio of shortest to largest sighting distance - x_e - time already spent handling a prey item - rate of prey loss during prey handling - prey escape rate during pursuit - prey biomass density (xw) - , T maximum time still to be spent handling a prey item - _e meal duration - _m maximum handling time ( _e+ _p) - _p duration of successful pursuit - _pm maximum duration of successful pursuit (_p(0)) - hazard rate - _m maximum of hazard rate - scaled functional response (wF) - minimal i-state space     

Changes of fluorescence lifetime and rotational correlation time of bovine serum albumin labeled with 1-dimethylaminonaphthalene-5-sulfonyl chloride in guanidine and thermal denaturations

The nanosecond fluorescence depolarization method was applied to measure the fluorescence lifetime () and the rotational correlation time () of bovine serum albumin (BSA) labeled with 1-dimethylaminonaphthalene-5-sulfonyl chloride (dansyl-Cl). Changes of and of dansyl BSA in the guanidine denaturation and in the thermal denaturation were examined. In parallel, the secondary structural change of dansyl BSA was followed by circular dichroism measurements. The magnitude of was almost unchanged between 1 and 2 M guanidine, where the secondary structure of the protein was predominantly disrupted; whereas that of began to increase before the disruption of secondary structure in the guanidine denaturation. In the thermal denaturation, in contrast, changes of both and occurred in a temperature range where the secondary structure was predominantly disrupted. The volume of equivalent sphere (V _e ) and the axial ratio () for the BSA were 3.6–3.8×10^–19 cm³ and 3.6 at 2M guanidine as against 2.1×10^–19 cm³ and 2.2 in the absence of guanidine (25°C), respectively. The magnitudes ofV _e and were 4.9×10^–19 cm³ and 4.5 at 65°C, respectively. Although the secondary structural change of dansyl BSA was irreversible in the thermal denaturation,V _e and were reversible.     

Modelling endplate currents: dependence on quantum secretion probability and decay of miniature current

Quantification of the time course and amplitude of endplate currents (EPC) was made with respect to dispersion of quanta secretion and to changes in the exponential decay of miniature endplate currents (_mepc). The relationship between RPC amplitude and _mepc follows a double-exponential curve with ₁= 0.3 ms and ₂ = 6 ms. If the amplitude of fully synchronised EPC is taken as 100%, then the loss of EPC amplitude is already 42% with physiological parameters of dispersion (the half-rise and decay constant of distribution of secretion probability = 0.5 ms, _mepc =1 ms). This loss is even more substantial if secretion is more dispersed or miniature endplate currents decay faster. Correspondence to: F. Vyskocil     

"Velocity leakage" in the pigeon vestibulo-ocular reflex

The transfer characteristics of the vestibuloocular reflex (VOR), and of the semicircular canal primary afferents (SCPAs) that drive it, have been studied in several species. In monkeys and cats, the dominant time constant describing horizontal VOR dynamics ( _hu ) is longer than that ( _c ) of horizontal SCPAs. This lengthening of the time constant has been attributed to a velocity storage mechanism that has been modeled as a positive feedback loop in the VOR pathways. We have studied the transfer characteristics of horizontal and vertical VOR and SCPAs in unanesthetized pigeons. In this species the dominant time constants of both the horizontal and vertical VOR ( _hv and _vv ) are shorter than _c . This finding indicates that time constants characterizing the lower frequency response of the VOR can be lengthened or shortened depending on the species. We propose that in the pigeon the velocity leakage mechanism can be modeled by substituting negative feedback for positive feedback in the model of the VOR pathways. Negative feedback can also account for the further shortening of _hu and _vv as VOR gain increases with arousal. Additionally, making the negative feedback loop nonlinear can model the dependency of lower frequency VOR phase on amplitude, and skew in VOR waveforms. Pigeon VOR and SCPA dynamics also differ in their adaptive properties and higher frequency behavior. A predominance of input from highly adaptive SCPAs is proposed to account for the increased adaptation of the vertical VOR as compared with SCPAs overall. A pure time-delay associated with VOR operation can explain the phase lag of the VOR relative to SCPAs at higher frequencies.     

Die Aktivit?tsperiodik bei V?geln mit und ohne dunklem Schlafkasten

Zusammenfassung In 2 Versuchsserien wurden Kohlmeisen(Parus major) und japanische Möwchen(Lonchura striata var.domestica) einzeln und schallisoliert gehalten. In der ersten Versuchsserie, in der alle Vögel einen dunklen Schlafkasten hatten, wurde der Einfluß der Beleuchtungsstärke auf die Periode () der Hüpfaktivität und auf das Verhältnis von Aktivitätszeit zu Ruhezeit ( : -Verhältnis) untersucht. Sowhol Kohlmeisen als auch japanische Möwchen folgen der Regel, daß mit wachsender Beleuchtungsstärke die Periode kürzer und das : -Verhältnis größer wird.In der 2. Serie wurde der Einfluß Ruhe im dunklen Schlafkasten auf die Periodenlänge und auf das : -Verhältnis untersucht. Es wurden die Messungen aus Bedingung 1 (der Vogel hat einen dunklen Schlafkasten zur Verfügung) mit den Messungen aus Bedingung 2 (der Vogel hat keinen oder einen hellen Schlafkasten zur Verfügung) verglichen. Das Ergebnis bei Kohlmeisen entspricht den Befunden bei konstantem Licht verschiedener Intensität. Unter Bedingung 1 ist länger und das : -Verhältnis kleiner als in Bedingung 2. Das Ausmaß der Änderung von nach Fortnahme des dunklen Kastens ist unabhängig von der Periodenlänge in Bedingung 1. Das Ausmaß der änderung von : ist unabhängig von a : in Bedingung 1, jedoch schwach negativ korreliert mit der Periodenlänge in Bedingung 1.Bei japanischen Möwchen entsprechen die Ergebnisse dieser Versuchsserie nicht der Regel für tagaktive Vögel. Mit Benützen des dunklen Schlafkastens ist kürzer als ohne den Schlafkasten. Ohne den Schlafkasten ist etwa 24 Std. Das : -Verhältnis ist in Bedingung 1 unter bestimmten Voraussetzungen kleiner als in Bedingung 2. Das Ausmaß der Änderung von nach Fortnahme des Kastens ist mit der dazugehörigen Periode in Bedingung 1 hochsignifikant korreliert (Regressionskoeffizient b=-1.01, Korrelationskoeffizient r=0.89). Ebenfalls ist das Ausmaß der Änderung von : nach Fortnahme des Kastens mit : aus Bedingung 1 korreliert; es scheint, als würde ein bevorzugtes : -Verhältnis von etwa 2.0 eingeregelt.Die Ergebnisse werden im Hinblick auf 4 Punkte diskutiert: 1) Das circadiane System arbeitet innerhalb eines engen Bereiches von - und : -Werten optimal. 2) Der Optimalbereich wird bevorzugt unter ungünstigen Bedingungen angestrebt. 3) Der Entzug des dunklen Schlafkastens belastet japanische Möwchen mehr als Kohlmeisen. 4) Bei japanischen Möwchen wird in Bedingung 1 durch fortplfanzungsphysiologischen Einfluß verkürzt.

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Circadian activity rhythms of birds with and without a dark nest box

Summary Perch-hopping activity of Great tits(Parus major) and Bengales finches(Lonchura striata domestica), housed individually in soundproof boxes, was studied in two series of experiments. In the first series all birds had access to a dark nest box, in which they retired during their subjective night. In this experiment the effect of light intensity on the freerunning circadian activity rhythm was investigated. Both Great tits and Bengalese finches obey the circadian rule by responding to an increase in light intensity with shortening the circadian period () and with an increase of the ratio of activity time and rest time ( : ).In the second series of experiments the influence of sleeping in the dark nest box on both circadian period and : -ratio was studied. The results of two experimental conditions — without and with access to a dark nest box — were compared. In the Great tits, the results are in agreement with the effect of light intensity: when a dark nestbox is available, is longer and the : -ratio is smaller than in the absence of a nest box. The magnitude of the change in free-running period after removal of the nest box is independent of the original value of ; the amount of change : -ratio is likewise independent of the original : -ratio, but is weakly correlated to the original .InLonchura striata var. domestica, removal of the dark nest box leads to a lenghtening of the free-running period to about 24 hours; the : -ratio is smaller in the presence of a dark nestbox, if certain other conditions are fulfilled. The magnitude of the change in after removal of the nest box is highly correlated to the original free-running period (r=-0.89) in such a way that, without nest box, the period approaches a value of 24 hours. Also, the amount of change in : -ratio due to nest box removal is negatively correlated to the original : -ratio. A probably preferred : -ratio of 2.0 is adopted.These results are discussed in the view of 4 points: 1) The circadian system operates at its optimum within a narrow range of - and : -values. 2) This optimal range is especially adopted when conditions become adverse. 3) Removal of the dark nest box results in a more stressful situation for Bengalese finches than for Great tits. 4) In the Bengalese finches, is shortened in the presence of a nest box due to effects on reproductive physiology.

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Herrn Prof. Dr. JürgenAschoff zum 60. Geburtstag gewidemt.     

Conformational dynamics of the anticodon loop in yeast tRNAPhe as sensed by the fluorescence of wybutine

Conformational and dynamic properties of the anticodon loop of yeast tRNA^Phe were investigated by analyzing the time resolved fluorescence of wybutine serving as a local structural probe adjacent to the anticodon GmAA on its 3 side. The influence of Mg²⁺, important for stabilizing the tertiary structure of tRNA, and of the complementary anticodon s²UUC of E. coli tRNA ₂ ^Glu were investigated.Fluorescence lifetimes and anisotropies were measured with ps time resolution using time correlated single photon counting and a mode locked synchronously pumped and frequency doubled dye laser as excitation source. From the analysis of lifetimes () and rotational relaxation times ( _R ) we conclude that wybutine occurs in various structural states: (i) one stacked conformation where the base has no free mobility and the only rotational motion reflects the mobility of the whole tRNA molecule (=6 ns, _R =19 ns), (ii) an unstacked conformation where the base can freely rotate (=100 ps, _R = 370 ps) and (iii) an intermediary state (=2 ns, _R = 1.6 ns).Under biological conditions, i. e. in the presence of Mg²⁺ and neutral salts, wybutine is found in a stacked and immobile state which is consistent with the crystallographic picture. In the presence of the complementary codon however, as exemplified by the E. coli-tRNA ₂ ^Glu anticodon, our analysis indicates that the codon-anticodon complex exists in an equilibrium of structural states with different rotational mobility of wybutine. The conformation with wybutine freely mobile is the predominant one and suggests that this conformation of the codon-anticodon structure differs from the canonical 3–5 stack.     

Residual motion of hemoglobin-bound spin labels and protein dynamics: viscosity dependence of the rotational correlation times

The residual motion of spin labels bound to cysteine 93 and to lysines of methemoglobin has been studied by electron paramagnetic resonance spectroscopy. To separate the influences of the solvent and the protein environment of the label fluctuations, the correlation times, , were analyzed as a function of temperature for fixed solvent viscosities, . Results show that over a wide range of viscosity the dependence of on may be empirically described by a power law ^k . The exponent k depends strongly on the location of the label on the protein surface. If one regards the spin labels as artificial amino acid side chains, characteristic values of correlation times and amplitudes of the rotational motion at the surface can be given. For =1 cP and T=297 K the correlation time of the labels bound to lysines is found to be =9 · 10^–10 s and the rotational diffusion is nearly isotropic. The spin label bound to cysteine 93 occupies a protein pocket, its rotational motion is therefore restricted. The correlation time of the label motion within a limited motion cone of semi angle =30° ± 3° is found to be =1.3 · 10^–9 s for =1 cP and T=297 K.     

Effects of moisture stress on the multiplication and expansion of cells in leaves of sugar beet

Summary Sugar beets were subjected to moisture stress by decreasing the water potential of the culture solution osmotically with polyethylene glycol by a known amount, , and, alternatively by applying matric potential, , at the plant roots. Lowering the water potential at the root surface less than 200 millibars by either method resulted in significant decreases in the rate of cell multiplication. The final number of cells per leaf at = -372 mb the final was 165% of that at = -473 mb ( = –101 mb); similarly at = –15 mb the final cell number was 198% of that at = –196 mb ( = –181 mb). The mean cell volume of leaves was not significantly affected by these levels of moisture stress.     

Activation kinetics of single high-threshold calcium channels in the membrane of sensory neurons from mouse embryos

Summary Activation kinetics of single high-threshold inactivating (HTI orN-type) calcium channels of cultured dorsal root ganglion cells from mouse embryos was studied using a patchclamp method. Calcium channels displayed bursting activity. The open-time histogram was single exponential with an almost potential-independent mean open time _op. The closed-time histogram was multicomponent; at least three of the components were associated with the activation process. The fast exponential component with the potential-independent time constant _cl ^f included all intraburst gaps, while two slower ones with potential-dependent time constants _cl ^vs described shut times between bursts and between clusters of bursts. The burst length histogram was biexponential. The fast component with a relatively potential-independent time constant _bur ^f described short, isolated channel openings while the slow component characterized real bursts with a potential-dependent mean life time. The waiting-time histogram could be fitted by a difference of two exponentials with time constants being the same as _cl ^s and _cl ^vs . The data obtained were described in the frame of a 4-state sequential model of calcium channel activation, in which the first two stages are formally attributed to potential-dependent transmembrane transfer of two charged gating particles accompanying the channel transitions between three closed states, and the third one to fast conformational changes in channel protein leading to the opening of the channel. The rate constants for all transitions were defined. The validity of the proposed model for both low-threshold inactivating (LTI orT-type) and high-threshold noninactivating (HTN orL-type) calcium channels is discussed.     

Electric field-induced breakdown of lipid bilayers and cell membranes: A thin viscoelastic film model

Summary A simple viscoelastic film model is presented, which predicts a breakdown electric potential having a dependence on the electric pulse length which approximates the available experimental data for the electric breakdown of lipid bilayers and cell membranes (summarized in the reviews of U. Zimmermann and J. Vienken, 1982,J. Membrane Biol. 67:165 and U. Zimmermann, 1982,Biochim. Biophys. Acta 694:227). The basic result is a formula for the time of membrane breakdown (up to the formation of pores): =(/C)/( _m ² ₀ ² U ⁴/24Gh ³+T ²/Gh–1), where is a proportionality coefficient approximately equal to ln(h/2₀),h being the membrane thickness and ₀ the amplitude of the initial membrane surface shape fluctuation ( is usually of the order of unity), represents the membrane shear viscosity,G the membranes shear elasticity modules, _m the membrane relative permittivity, ₀=8.85×10^–12 Fm,U the electric potential across the membrane, the membrane surface tension andT the membrane tension. This formula predicts a critical potentialU _c ;U _c =(24Gh ³/ _m ² ₀ ² )^1/4 (for = andT=0). It is proposed that the time course of the electric field-induced membrane breakdown can be divided into three stages: (i) growth of the membrane surface fluctuations, (ii) molecular rearrangements leading to membrane discontinuities, and (iii) expansion of the pores, resulting in the mechanical breakdown of the membrane.     

Interaction among anion,cation and glucose transport proteins in the human red cell

Summary The time course of binding of the fluorescent stilbene anion exchange inhibitor, DBDS (4,4-dibenzamido-2,2-stilbene disulfonate), to band 3 can be measured by the stopped-flow method. We have previously used the reaction time constant, _DBDS, to obtain the kinetic constants for binding and, thus, to report on the conformational state of the band 3 binding site. To validate the method, we have now shown that the ID₅₀ (0.3±0.1 m) for H₂-DIDS (4,4-diisothiocyano-2,2-dihydrostilbene disulfonate) inhibition of _DBDS is virtually the same as the ID₅₀ (0.47±0.04 m) for H₂-DIDS inhibition of red cell Cl^– flux, thus relating _DBDS directly to band 3 anion exchange. The specific glucose transport inhibitor, cytochalasin B, causes significant changes in _DBDS, which can be reversed with intracellular, but not extracellular,d-glucose. ID₅₀ for cytochalasin B modulation of _DBDS is 0.1±0.2 m in good agreement withK _D =0.06±0.005 m for cytochalasin B binding to the glucose transport protein. These experiments suggest that the glucose transport protein is either adjacent to band 3, or linked to it through a mechanism, which can transmit conformational information. Ouabain (0.1 m), the specific inhibitor of red cell Na⁺,K⁺-ATPase, increases red cell Cl^– exchange flux in red cells by a factor of about two. This interaction indicates that the Na⁺,K⁺-ATPase, like the glucose transport protein, is either in contact with, or closely linked to, band 3. These results would be consistent with a transport proteincomplex, centered on band 3, and responsible for the entire transport process, not only the provision of metabolic energy, but also the actual carriage of the cations and anions themselves.     

Application of the Criterion of Biological Time (τ n /τ0) to the Studies of Embryogenesis in Birds

It was shown on the example of chick embryo that the number ₀ ( _n /₀) can be recommended as a measure of biological time and, for this purpose, the duration of the minimal mitotic cycle during synchronous cleavage divisions should be determined (in minutes) in various avian species. Based on the preliminary data, one can propose the comparability and similarity of the temporal programs of gastrulation and somitogenesis in the chick embryo and embryos of some fish and amphibians.     

Die Aktivitätsperiodik von zwei tagaktiven Nagern,Funambulus palmarum undEutamias sibiricus,unter Dauerlichtbedingungen

Zusammenfassung Bei, in kleinen Käfigen mit Zugang zu einer Lauftrommel, einzeln gehaltenen Tieren der beiden ArtenFunambulus palmarum (Palmenhörnchen) undEutamias sibiricus (asiatisches Streifenhörnchen) wurde der Einfluß verschiedener Beleuchtungsstärke unter Dauerlichtbedingungen auf die circadiane Aktivitätsperiodik untersucht.4 Palmenhörnchen wurden in verschiedenen Beleuchtungsstärken von nicht meßbarer Intensität bis etwa 1000 Lux gemessen. Von etwa 1 Lux bis 1000 Lux war die Periodendauer () positiv mit der Beleuchtungsstärke korreliert. Über den gesamten Bereich der untersuchten Lichtintensitäten war die Aktivitätsmenge positiv mit dem Logarithmus der Beleuchtungsstärke (logI _LL ) korreliert. Es bestand jedoch ebenso wie zwischen und logI _LL keine lineare Beziehung zwischen beiden Größen (Fig. 1). Das Verhältnis Aktivitätszeit zu Ruhezeit (:) war bei allen untersuchten Tieren weder mit noch mit der Aktivitätsmenge korreliert.Von insgesamt 15 unter Dauerlichtbedingungen zwischen 0,01 und 100 Lux gemessenen asiatischen Streifenhörnchen zeigten nur 7 Tiere circadiane Perioden der Aktivität. Infolge der großen Streuung der Aktivitätsanfänge und -enden sowie des Aktivitätsmusters konnten a und : bei den meisten Tieren nicht bestimmt werden. Die -Werte streuten um einen mittleren Wert von 23,6 Std; sie zeigten jedoch keine regelhafte Abhängigkeit von der Beleuchtungsstärke (Fig. 5).Bei einzelnen Tieren beider Arten wurde bei Beleuchtungsstärken von etwa 3–4 Lux eine Aufspaltung (temporäre Dissoziation) einzelner Aktivitätskomponenten mit verschiedenen Frequenzen beobachtet (Figs. 2 und 4).Aufgrund der unterschiedlichen Abhängigkeit der Aktivitätsparameter (Aktivitätszeit und Aktivitätsmenge) von bei verschiedenen Tiergruppen wird vermutet, daß das Licht sowohl verschiedene Parameter der circadianen Aktivitätsperiodik als auch einzelne Komponenten des der Aktivität zugrunde liegenden circadianen Systems unabhängig voneinander beeinflußt. Tag- und nachtaktive Säuger unterscheiden sich im wesentlichen nur in den kritischen Beleuchtungsstärken, d.h. den Beleuchtungsstärken, bei welchen die kürzesten Perioden gemessen werden (Fig. 6).

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The activity rhythm of two day-active rodents,Funambulus palmarum andEutamias sibiricus, in continuous illumination

Summary Palm squirrels (Funambulus palmarum) and Sibirian chipmunks (Eutamias sibiricus) were kept individually in small cages attached to a running wheel. Under continuous illumination the influence of different light intensities on the circadian rhythm of activity was measured.Four palm squirrels were exposed to light intensities between unmeasurable intensity (total darkness) and about 1000 lux. Between 1 and 1000 lux the period length () of the circadian rhythm of activity was positively correlated with light intensity. The amount of activity per period showed a positive relationship with light intensity over the range of intensities tested (Fig. 1). In all 4 animals the ratio activity-time to rest-time (: ) was neither correlated with the amount of activity per period nor with .From a total of 15 Sibirian chipmunks tested under continuous illumination between 0.01 and 100 lux only 7 animals showed circadian rhythms of activity. As a consequence of the great variability of the beginning and the end of activity as well as in the temporal activity pattern, a (activity time) and : could not be determined in most animals of this species. The values of varied around a mean of 23.6 hr, but did not change as a function of light intensity (Fig. 5).In some individuals of both species a splitting or temporary dissociation of single components of activity with different frequencies was observed at light intensities of about 3 to 4 lux (Figs. 2 and 4).On the basis of the different relationships between the activity functions (amount of activity and activity-time) and in various groups of animals (cf. day-active mammals and birds), it is assumed that light acts separately on the parameters of the circadian activity rhythm as well as on single components of the circadian system underlying activity. Day- and night-active mammals differ essentially only in respect to their critical light intensities, i.e. the light intensities at which the shortest circadian periods are measured (Fig. 6).

     

Induced diploid gynogenesis and polyploidy in the ornamental (koi) carp Cyprinus carpio L.

The results of a series of experiments conducted in our laboratory on the ornamental common carp (koi), aimed at optimizing heat-shock chromosome-set manipulation procedures, are described. The timing of heat-shock initiation was expressed in the relative unit of embryological age (₀) in order to standardize this parameter, the absolute time for heat-shock initiation being calculated from duration of one ₀ at two different pre-treatment water temperatures. Heat shocks were applied within the periods of 0.05–0.60 ₀ and 1.20–2.20 ₀ which, respectively, cover the successive phases of the 2nd meiotic division and the 1st cleavage. The highest production of diploid gynogenetic offspring was observed when heat shocks were initiated at 0.15–0.25 ₀ and at 1.5 ₀, after insemination, corresponding to anaphase of meiosis-II, and metaphase of the 1st cleavage, respectively. Similar results were obtained irrespective of the different pre-treatment water temperatures, thus confirming the possibility of standardizing heat-shock timing by ₀.     

Cyclic modes in artificial neural nets

Artificial neural nets constructed of dicrete populations of 200–1000 formal neurons have been studied through computer simulation. Among the basic assumptions of operation of these nets are the following: a) Each neuron fires at times which are integral multiples of the synaptic delay . b) It produces the appropriate PSP's after . c) All the neurons have the same refractory period and d) temporal summation occurs without decrement, for a period less than the synaptic delay. The nets were specified by a number of parameters: fraction of inhibitory neurons in the population, average number of connections to each cell, threshold for cell firing. These parameters did not determine the detailed microscopical structures of nets which was established separately on a random basis.For the range of the parameters considered in this study it was found that neural nets are capable of supporting self-maintaining activity in the form of cycling modes, characterized by a fixed period. The period of the cycles can be altered by a steady, non-cycling external input to the net. Evidence is presented that the cycling modes depend upon the statistical parameters of the net and the stimulus characteristics rather than on the detailed structure of the net. These results suggest that non-structured nerve nets may respond in specific manner to specific stimuli.

Glossary

Parameters of Neural Net Model Synaptic delay - A Total number of neurons in the netlet - h Fraction of inhibitory neurons in the netlet (in % of total number of neurons) - ⁺ Average number of axon branches emanating from anexcitatory neuron - ^– Average number of axon branches emanating from an inhibitory neuron - k ⁺ Average EPSP produced by an excitatory neuron in arbitrary units of amplitude - k ^– Average IPSP produced by an inhibitory neuron in arbitrary units of amplitude - Firing threshold of neurons in the netlet - The minimum number of ESPS's necessary to trigger a neuron in the absence of inhibitory inputs - The minimum number of ESPS's necessary to trigger a neuron in the presence of inhibitory inputs. Dynamic Parameters of the Model n An integer giving the number of elapsed synaptic delays (i.e. elapsed time) - _n The activity; i.e. the fraction of active neurons in the netlet at t=n (the actual number of active cells is given by _nA) - _n={ⁱ_n} State vector of single netlet at time n This research has been supported by NIH grants NS-8012 and NS-8498, and NSF grant GB-30498. Computation assistance was provoded by the Health Sciences Computing Facility, UCLA, sponsored by NIH Special Research Resources grant RR-3.     

Effects of zwitterionic detergents on the electronic structure of the primary donor and the charge recombination kinetics of P+Q A − in native and mutant reaction centers from Rhodobacter sphaeroides

The effects of detergents on the electronic structure of the oxidized primary donor P⁺ and the time constant _AP of the P⁺Q _A ^– charge recombination at ambient temperatures have been investigated in native and mutant reaction centers (RCs) from Rhodobacter sphaeroides. It is shown that N-lauryl-N,N-dimethyl-3-ammonio-1-propane sulfonate (SB12) induces a transition to a second distinct conformation of the RC. In the case of the wild type and the mutant FY(M197), in which a hydrogen bond is introduced to the 2-acetyl group of the dimer half of P that is associated with the M-subunit of the RC, the conformational change causes a more asymmetric spin density distribution between the two bacteriochlorophyll moieties of P⁺ in favor of the L-half. For both types of RCs the time constant _AP depends on the SB12/RC ratio as does the position of the long-wavelength band of P, _max. The increase of _AP by 30 ms and the shift of _max from 866 nm to 851 nm are indicative for the conformational change. In addition, a smaller linear increase of _AP with increasing SB12/RC ratio is superimposed on the variation of _AP due to the conformational change. Similar effects of SB12 on the optical spectra as well as on _AP are also observed for the two heterodimer mutants HL(L173) and HL(M202), in which one of the bacteriochlorophylls of P is replaced by a bacteriopheophytin. There are no clear indications for a correlation of _AP with the localization of the positive charge in P⁺. Furthermore, it is concluded from the dependence of _AP on the SB12/RC ratio that the single-site mutations do not affect the standard free energy difference of the two conformations to a measurable extent.     

Existence and uniqueness of a sharp travelling wave in degenerate non-linear diffusion Fisher-KPP equations

In this paper we use a dynamical systems approach to prove the existence of a unique critical value c ^* of the speed c for which the degenerate density-dependent diffusion equation u _ct = [D(u)u _x ] _x + g(u) has: 1. no travelling wave solutions for 0 < c < c ^*, 2. a travelling wave solution u(x, t) = (x - c ^* t) of sharp type satisfying (– ) = 1, () = 0 ^*; '(^*–) = – c ^*/D'(0), '(^*+) = 0 and 3. a continuum of travelling wave solutions of monotone decreasing front type for each c > c ^*. These fronts satisfy the boundary conditions (– ) = 1, '(– ) = (+ ) = '(+ ) = 0. We illustrate our analytical results with some numerical solutions.