Stimulus-evoked slow potential shifts and changes in [K+]0 of the frog optic tectum

Summary In 17 frogs (Rana esculenta var ridibunda) immobilised with succinyl choline the optic tectal surface was stimulated by trains of electrical pulses or by a flash to the contralateral eye. Sustained potential shifts (SPSs) and changes in extracellular potassium concentration ( [K⁺]₀) were simultaneously recorded.In response to electrical stimulation SPSs of maximal amplitudes (1.19±0.1 mV) were recorded between 50 and 200 m in depth and maximal [K⁺]₀ (0.69 ±0.08 mM) between 100 and 350 m. The changes of SPS and [K⁺]₀ showed a close similarity in experiments with changes in voltage, pulse duration and frequency of stimuli within a train. The induced SPS had a duration of 28±1.54 s, the [K⁺]₀ of 32±1.23 s.The flash stimulus induced an SPS and [K⁺]₀ of maximal amplitudes between 50 and 200 m in depth with values of 0.57±0.1 mV and 0.29±0.03 mM respectively. An additional wave with a latency of ca 1 s and a duration of ca 3 s arose on the background of the SPS to a flash stimulus, associated with an additional increase in [K⁺]₀.It is considered that the accumulation of K⁺ in extra-cellular space, with neuronal activity, results in depolarization of radial processes of ependymal glia. This is reflected in the neuropil of the upper layers of the optic tectum as an SPS.We would like to dedicate this article to the memory of Alexander Roitbak who died as a result of a tragic accident while this paper was in press. He will be remembered fondly especially for his contributions to understanding of the functions of Neuroglia. E.V.O., P.R.L., T.A.R.     

Pioneer and late stage tropical rainforest tree species (French Guiana) growing under common conditions differ in leaf gas exchange regulation,carbon isotope discrimination and leaf water potential

Leaf gas exchange rates, predawn _wp and daily minimum _wm leaf water potentials were measured during a wet-to-dry season transition in pioneer (Jacaranda copaia, Goupia glabra andCarapa guianensis) and late stage rainforest tree species (Dicorynia guianensis andEperua falcata) growing in common conditions in artificial stands in French Guiana. Carbon isotope discrimination () was assessed by measuring the stable carbon isotope composition of the cellulose fraction of wood cores. The values were 2.7 higher in the pioneer species than in the late stage species. The calculated time integratedC _i values derived from the values averaged 281 mol mol^–1 in the pioneers and 240 mol mol^–1 in the late stage species. The corresponding time-integrated values of intrinsinc water-use efficiency [ratio CO₂ assimilation rate (A)/leaf conductance (g)] ranged from 37 to 47 mmol mol^–1 in the pioneers and the values were 64 and 74 mmol mol^–1 for the two late stage species. The high values were associated—at least inJ. copaia—with high maximumg values and with high plant intrinsinc specific hydraulic conductance [Cg/(_wm–_wp], which could reflect a high competitive ability for water and nutrient uptake in the absence of soil drought in the pioneers. A further clear discriminating trait of the pioneer species was the very sensitive stomatal response to drought in the soil, which might be associated with a high vulnerability to cavitation in these species. From a methodological point of view, the results show the relevance of for distinguishing ecophysiological functional types among rainforest trees.     

Visual unit,EEG and sustained potential shift responses to biologically significant stimuli in the brain of toads (Bufo bufo)

Summary Visual unit activity, EEG changes and sustained potential shifts (SPS) were recorded from the toad tectum whilst the animal was presented with a visual stimulus. Telencephalic EEGs were also recorded.On the surface of the tectum, retinal unit activity preceded a sustained negative shift in potential and an increase in the amplitude and dominant frequency of the EEG. In deeper layers of the tectum, T5 units with configurational selectivity for wormlike stimuli were found. The activity of these units followed a pronounced SPS and EEG change.Visual unit activity was most pronounced during the negative-going phase of the synchronised EEG, when there was also a small decrease in amplitude of neuronal spikes. Similarities between the latencies and durations of EEGs and SPSs, and their response decrements, on repeated stimulus presentation, implies a close relationship between them not shared by the visual units studied. The specific activity of tectal units is discussed in relation to the correlated EEG and SPS changes, which may form part of an adaptive sensitizing mechanism.Abbreviations EEG electroencephalogram - ERF excitatory receptive field - SPS sustained potential shift - T4, T5 tectal neurons     

Sustained potential shifts and changes in acoustic evoked potentials after presentation of a non-acoustic priming stimulus to carp (Cyprinus carpio).

1. Recordings were made from the region of the midbrain tectum and torus semicircularis of sustained potential shifts (SPS) to a non-acoustic priming stimulus and the change in subsequent acoustic evoked potentials (AEPs) to a train of six clicks after a long rest. 2. In the absence of priming stimuli (a jet of saline or water to the flank) the AEP to the first click in a train had the highest amplitude; with these stimuli it became the most attenuated. 3. The SPS to both non-acoustic stimuli was initially (ca 4 sec) negative, then became positive for a similar time period. 4. After saline jet the tectal and the torus AEP amplitude was significantly correlated with the torus SPS; after water jet, the tectal and the torus AEP durations were correlated with the SPS. 5. Application of alumina gel to the posterior telencephalic border caused elevation of the torus AEP amplitude after some 5 hr.     

Changes in EEG power, acoustic evoked potentials and heart rate after mildly arousing non-acoustic priming stimuli in carp (Cyprinus carpio).

1. Changes in EEG power spectrum of carp to a priming non-acoustic stimulus followed by acoustic clicks were compared to those due to acoustic clicks delivered alone. Recordings were made from the telencephalon, midbrain and medulla. Acoustic evoked potentials (AEPs) to the clicks were also recorded. 2. EEG power changes to non-acoustic stimuli occurred over the whole 1-40 Hz frequency range and were regionally specific and consistent. 3. The changes in the EEG midfrequency 12-24 Hz power spectrum to non-acoustic stimuli were significantly correlated with changes in the AEP to subsequent clicks. An elevated medullary AEP amplitude and reduced duration were correlated with increased medullary EEG power and increased midbrain AEP duration. 4. Telencephalic EEG power changes were inversely related to changes in medullary and midbrain AEP amplitude.     

Marked reduction in intramembranous particle clusters in the terminal portion of inner medullary collecting ducts of antidiuretic rats

Summary Antidiuretic hormone (ADH) induces an aggregation of intramembranous particles (IMP) into discrete clusters in the luminal plasma membrane of rat renal papillary collecting duct cells (Harmanci et al. 1978). The correlation between an elevated dose of ADH, increased urine osmolality, and greater IMP cluster frequency has led to speculation that the water permeability of the luminal plasma membrane is reflected by the IMP cluster density (Harmanci et al. 1980). The present study indirectly evaluated this water permeability by quantitating collecting duct IMP cluster frequency from freeze fracture replicas in two regions of the renal papilla, at its base and at its tip, in antidiuretic and in water diuretic rats. During antidiuresis there was a high frequency of IMP clusters (189/100 m² of luminal plasma membrane) in cells from the papilla base but not at the papilla tip (9.0/100 m²). During water diuresis there were few IMP clusters in either cells from the papilla base (5.9/100 m²) or at the papilla tip (1.4/100 m²). Most significantly these results suggest that the water permeability of the terminal portion of the inner medullary collecting duct of antidiuretic rats is significantly lower than that of the collecting duct epithelium higher in the papilla.Preliminary findings of this study were presented at the Second International Congress of Cell Biology, West Berlin 1980     

Changes in early acoustic-evoked potentials by mildly arousing priming stimuli in carp (Cyprinus carpio).

1. Averaged acoustic-evoked potential (AEPs) in the medulla and midbrain were recorded, as were changes in heart rate, indicating arousal, to a previous non-acoustic priming stimulus. 2. Useful AEP measures were amplitude of the early biphasic wave (less than 10 msec) in medulla and amplitude and duration of this wave in midbrain. 3. There was a negative regression of heart rate and medullary AEP amplitude especially evident for a 2 sec light stimulus. Decreased AEP amplitude in both regions was induced by water movement and an increase in midbrain AEP duration by the tactile stimulus. 4. Arousal effects even on these early AEP measures are specific to the form of arousing stimulus.     

Relationship between ecg,eeg and sps responses during arousal in the goldfish (Carassius auratus)

• 1.1. Goldfish (Carassius auratus) were fitted with ECG electrodes and intra-cranial stainless steel electrodes to monitor cardiac, EEG and SPS responses, during minimal restraint, to presentation of environmental stimuli (light-on, moving shadow, tap).
• 2.2. All three stimuli evoked a bradycardia and increases in the EEG frequency; correlates of arousal responses in fish.
• 3.3. EEG frequency changes were most evident in the fore- and midbrain regions; in the hindbrain smaller responses nevertheless showed discrimination between stimuli.
• 4.4. EEG amplitude changes were more site- and stimulus-specific than frequency changes.
• 5.5. SPSs occurred on stimulus presentations which were negative in polarity in the midbrain and positive in the forebrain and hindbrain, though the latter were smaller and less consistent.
• 6.6. Principal components analyses and regression analyses were used to examine detailed associations between peripheral and central physiological changes.
• 7.7. It was found that increases in the EEG frequency of fore- and midbrain regions were related to cardiac deceleration on early stimulus presentations.
• 8.8. This was also shown for the negative SPS of the midbrain to the presentation of the tap stimulus.
• 9.9. Positive SPSs of the forebrain were related to the bradycardia on later stimulus presentation i.e. during habituation of the arousal response.
• 10.10. The results indicate that in fish, as in other vertebrates, negative SPSs in the midbrain are associated with arousal and implicate the forebrain in the modulation of arousal by its habituation.

     

Circadian activity of the red squirrel,Tamiasciurus hudsonicus,in continuous darkness and continuous illumination

In order to examine the effects of constant conditions on wheelrunning activity, 58 red squirrels (Tamiasciurus hudsonicus ) were taken directly from the field and placed in either total darkness (DD) or continuous illumination (LL) 500 lux, for up to 70 days. The squirrels were sampled at various times of the year so that seasonal changes in the endogenous rhythm could be examined. The initial phasing of activity correlated with the photoperiod in the field and had a free-running period () close to 24 hours. However, increased in a nearly linear fashion, averaging about 0.19 min/day for squirrels in DD and about 0.87 min/day for squirrels in LL. All animals in LL had rhythms which eventually became dissociated into two or more components. On the other hand, squirrels kept in DD had running patterns which usually remained intact. After being in constant conditions for between 20 and 70 days, 28 squirrels were subjected to step transitions in illumination from DD to LL (500, 350 or 200 lux) or vice versa. An increase in illumination level generally resulted in a phase advance and a decreased. A decrease in illumination level generally resulted in a phase delay and increased. The maximum amount of activity occurred at some critical intensity between 200 and 350 lux. The free-running period was directly correlated with the entrainment phase-angle difference. This relationship was compared to the red squirrel's light-pulse response curve. These data support Pittendrigh's (1965) entrainment model.Presented during the Seventh International Biometeorological Congress, 17–23 August 1975, College Park, Maryland, USA.     

Macroalgal photosynthesis near the southern global limit for growth; Cape Evans,Ross Sea,Antarctica

Photosynthetic characteristics of the red macroalgae Phyllophora antarctica and Phymatolithon foecundum collected from under sea ice at Cape Evans, McMurdo Sound (Ross Sea) were determined using in situ fluorometric and lab-based oxygen exchange techniques. Only 0.16% of incident irradiance penetrated the 2.5 m thick ice cover and photosynthetic parameters for both taxa were characteristic of highly shade-adapted plants. Saturation onset parameter (E _k) did not exceed 13 mol photons m^-2 s^-1 in either taxon. For Phyllophora antarctica the light saturated photosynthetic rate at –1^°C was 10 mol O₂ g^-1 FW h^-1 and respiration averaged 3.3 mol O₂ g^-1 FW h^-1 between sampled depths of 10 and 25 m. A light meter deployed at 15 m depth for a year recorded a marked increase in underwater irradiance on the last day of January 2002 coinciding with ice-breakout, and a maximum value for irradiance of 120 mol photons m^-2 s^-1 on 9 February 2002. The 2-month ice-free period was the only time when irradiance consistently exceeded compensation (photosynthesis=respiration) and enabled Phyllophora antarctica to accumulate sufficient carbon to result in a measurable increase in thallus area equivalent to a biomass increment of 1.87 mg (DW) per frond. Near the southern global limit for marine macroalgae, conditions that dictate the availability of underwater irradiance are extremely variable from year to year. Low respiration rates enhance longevity of the Phyllophora antarctica thallus, enabling it to not only survive the winter darkness, but also to retain photosynthetic capacity and thus take advantage of windows of higher irradiance.     

Some properties of 2-5A binding/nucleolytic activities in gel filtered rabbit reticulocyte lysates

Rabbit reticulocyte lysates, gel filtered on Sephadex G-25 with or without ATP (or its analogs), were preincubated at 37°C and their subsequent binding to p₃A₄,3-[³²P]pCp was studied. Lysates filtered without ATP or in the presence of 0.1 mM 8-bromo-ATP, 1,N⁶-etheno-ATP, or ITP showed a time-dependent decrease in binding activity. This decrease was completely prevented when lysates were filtered with 0.1 mM ATP, 2-deoxy-ATP, --methylene-ATP, or ATP--S. The stability of binding provided by ATP or 2-deoxy-ATP analogs corresponds to a more active 2–5A dependent endonucleolytic (RNAase L) activity based on studies using [³H] viral mRNA. Chromatography on heparin-agarose showed that ATP-supplemented gel-filtered reticulocyte lysates had a different p₃A₄,3-[³²P]pCp binding activity elution-profile than lysates gel-filtered in the absence of ATP. Covalent cross-linking of periodate-oxidized p₃A₄,3-[³²P]pC to gelfiltered lysates, preincubated at 0°C or 37°C for 30 min, showed the following results: (1) all lysates gave a major cross-linking of the radioactive ligand to an 80 000 dalton polypeptide, regardless of the temperature of preincubation, (2) Iysates gel-filtered without ATP, with 0.1 mM ITP, or --methylene-ATP, showed a significant reduction in the cross-linking of the 80 000 dalton protein, after preincubation at 37°C for 30 min. This decrease was accompanied by an increase in the labeling of two smaller polypeptides.Abbreviations used 2 5-oligoadenylates oligonucleotides consisting of 5-adenylic acid residues joined by a 2 5-phosphodiester linkage     

Membrane potential and surface potential in mitochondria: Uptake and binding of lipophilic cations

Summary The uptake and binding of the lipophilic cations ethidium⁺, tetraphenylphosphonium⁺ (TPP⁺), triphenylmethylphosphonium⁺ (TPMP⁺), and tetraphenylarsonium⁺ (TPA⁺) in rat liver mitochondria and submitochondrial particles were investigated. The effects of membrane potential, surface potentials and cation concentration on the uptake and binding were elucidated. The accumulation of these cations by mitochondria is described by an uptake and binding to the matrix face of the inner membrane in addition to the binding to the cytosolic face of the inner membrane. The apparent partition coefficients between the external medium and the cytosolic surface of the inner membrane (K' _o) and the internal matrix volume and matrix face of the inner membrane (K' _i) were determined and were utilized to estimate the membrane potential from the cation accumulation factorR _c according to the relation =RT/ZF ln [(R _cV_o–K'_o)/(V_i+K'_i)] whereV _o andV _i are the volume of the external medium and the mitochondrial matrix, respectively, andR _c is the ratio of the cation content of the mitochondria and the medium. The values of estimated from this equation are in remarkably good agreement with those estimated from the distribution of⁸⁶Rb in the presence of valinomycin. The results are discussed in relation to studies in which the membrane potential in mitochondria and bacterial cells was estimated from the distribution of lipophilic cations.     

Propagated fluctuations of the electric potential in the apoplasm of Lepidium sativum L. roots

The electric potential on the surface of the Lepidium sativum L. root apex was recorded by means of six non-polarizable electrodes. Nonevoked fluctuations of the potential with amplitudes below 0.1 mV were observed. The fluctuations could be reversibly inhibited either by ether vapor or by anoxia caused by N₂. They did not occur in killed roots. Cross-correlation analysis of the fluctuations from six electrodes located one above another along the 3-mm apical region showed a pattern of time delay which indicates that the fluctuations may be the consequence of signals propagated in the root with a velocity of 3–9 mm · s^–1 in a basipetal direction from the root cap. We hypothesize that the fluctuations are due to signals of an unknown nature propagated along an intrasymplasmic continuous system, the symreticulum, composed of the cortical ER of individual cells and desmotubules passing through the plasmodesmata.Abbreviations AC alternating current - AP action potential - ACF autocorrelation function - CCF cross-correlation function - DC direct current - EEP extracellular electric potential This research was supported by Bundesminister für Forschung und Technologie, Bonn, and Ministerium für Wissenschaft und Forschung, Düsseldorf, (AGRAVIS). We are grateful to Mr. Dipl.-Ing. P. Blasczyk for constructing the amplifiers and for advice in instrumentation, and to Mr. H. Laubach for constructing the mechanical assembly.     

A negative selection scheme for tobacco protoplast-derived cells expressing the T-DNA gene 2

The amido hydrolase encoded by the T-DNA gene 2 catalyzes the conversion of indole-acetamide, -naphthalene acetamide, and other substrate analogues into the corresponding auxins. As a result, only gene 2-expressing protoplast-derived tobacco cells can grow in medium containing low concentrations (0.2–1 M) of -naphthalene acetamide as auxin precursor. However, in a mixture of SR1 and SR1, gene 2 ⁺ protoplast-derived cells, cross-feeding occurs and consequently no positive selection for gene 2 is obtained. A 100-times higher concentration of -naphthalene acetamide (between 30 and 300 M) provides a negative selection scheme. Only the tobacco cells expressing gene 2 are sensitive to the high naphthalene acetamide concentration and cannot grow to colonies, while cells lacking the gene 2 product regenerate calli even in mixed gene 2 ⁺ and gene 2 ^– cell populations. Thus, gene 2 might provide a unique biochemically defined marker to investigate mutations and gene inactivation.     

Dependence of the membrane potential of Chara cells on external pH in the presence or absence of internal adenosinetriphosphate

The dependence of the membrane potential (E_m) and the membrane resistance (R_m) of Chara australis R. Brown on the pH of the external medium (pH₀) was studied by controlling the activity of the plasmamembrane H⁺ pump under both light and dark conditions. The activity of the pump was controlled by regulating the internal ATP or Mg²⁺ concentration in tonoplast-free cells prepared by vacuolar perfusion. In these cells, which contained Mg · ATP (mgATP cells), E_m and R_m were very sensitive to pH₀, as in normal cells. E_m was more negative in light than in the dark at all pH₀ values tested. Tonoplast-free cells with very low [ATP]_i (-ATP cells) or [Mg²⁺]_i (-Mg cells) showed very weak dependence of E_m and R_m on pH₀. Thus, the active and not the passive component of E_m was sensitive to pH₀. At the same time, the high permeability of the plasma membrane to H⁺ was questioned. In both-ATP cells and-Mg cells, E_m was scarcely affected and R_m markedly decreased on illumination.Abbreviations CyDTA 1,2-cyclohexanediamine-N,N-tetraacetic acid - EGTA ethyleneglycol-bis-(-aminoethylether)N,N-tetraacetic acid - HK hexokinase     

Effect of Naloxone on the Activity of Cl–-Activated Mg2+-ATPase from Plasma Membrane Fraction of Bream Brain (Abramis brama L.) in the Presence of GABAa-ergic Substances

We studied the effect of naloxone—an antagonist of the opioid receptors—on sensitivity of Cl^–-activated Mg²⁺-ATPase from the plasma membrane fraction of bream brain (Abramis brama L.) to GABA_a-ergic substances. Preincubation of the plasma membranes with 1–100 M naloxone increased the basal Mg²⁺-ATPase activity and suppressed its activation by chloride ions. The same effects were observed in the presence of the agonists of GABA_a/benzodiazepine receptors: 0.1–100 M GABA, 1–500 M pentobarbital, and 0.1–100 M phenazepam. Naloxone (10 M) inhibited activation of the basal Mg²⁺-ATPase by the studied ligands and restored the enzyme sensitivity to Cl^–. However, the effect of naloxone was not observed in the presence of high concentrations of pentobarbital (500 M) and phenazepam (100 M). The obtained data show that naloxone modulates the activity of Cl^–-activated Mg²⁺-ATPase from the plasma membranes of bream brain and antagonizes the GABA_a receptor ligands.     

Studies on Tn951 (lac+) expression in Agrobacterium

Summary None of the Agrobacterium tumefaciens and A. rubi strains tested produces detectable amounts of -galactosidase although they are capable of utilizing lactose as sole source of carbon. This opportunity was taken to investigate the expression of lac transposon Tn951 (Cornelis et al. 1978) in Agrobacterium with the ultimate goal of using this system to investigate alien gene expression. When the transposon was introduced with the help of a broad-host range plasmid, RP1, the transconjugants produced significant quantities of -galactosidase which was inducible by isopropyl--D-thiogalactopyranoside. Tn951 was capable of restoring the Lac⁺ phenotype to an A. tumefaciens mutant not capable of using lactose. Cellobiose, a known inducer of aldohexopyranoside: cytochrome c oxidoreductase which regulates the characteristic 3-ketolactose production in Agrobacterium: van Beeumen and De Ley (1968), had no effect on -galactosidase activity.Abbreviations NCPPB National Collection of Plant Pathogenic Bacteria, Harpenden - km kanamycin resistance - str streptomycin resistance - rif ^r rifampicin resistance     

Regulation of adenosine 5′-phosphosulfate sulfotransferase activity by H2S and cyst(e)ine in primary leaves of Phaseolus vulgaris L.

During chloroplast development in the primary leaves of Phaseolus vulgaris, the extractable activity of adenosine 5-phosphosulfate sulfotransferase increased ten-fold. When chloroplast development took place in air enriched with 3.5 l H₂S·l^-1 there was a decrease in adenosine 5-phosphosulfate sulfotransferase activity. Cyst(e)ine in concentrations up to 1 mM (in the external medium) did not affect the increase in adenosine 5-phosphosulfate sulfotransferase activity in intact plants. In plants with excised roots, 0.75 mM cyst(e)ine inhibited this increase. In green primary leaves, H₂S or cyst(e)ine treatment resulted in a decrease of extractable adenosine 5-phosphosulfate sulfotransferase activity. In intact plants, this effect of cyst(e)ine was observed at a concentration of 1 mM, and in plants with excised roots, 0.25 mM had a comparable effect.In developing plants, the extractable activities of O-acetyl-L-serine sulfhydrylase (EC 4.2.99.9) and ribulosebisphosphate carboxylase (EC 4.1.1.39.) were not affected by H₂S or cyst(e)ine.Abbreviations APS adenosine 5-phosphosulfate - APSSTase adenosine 5phosphosulfate sulfotransferase - BSA bovine serum albumin - DTE dithioerythritol - EDTA ethylenediaminetetra-acetic acid - OASSase O-acetyl-L-serine sulfhydrylase - PAPS adenosine 3-phosphate 5-phosphosulfate - POPOP 1,4 Di 2-(5-phenyloxazolyl)-benzene - PPO 2,5-diphenyloxazol - RubP ribulose-bisphosphate - RubPCase ribulosebiphosphate carboxylase This is no. 8 in the series Regulation of Sulfate Assimilation in Plants. The term cysteine is used when it is clear that cystine is not involved; cyst(e)ine is used for an undefined mixture of cysteine and cystine. The concentrations are expressed in all cases relative to cysteine     

Evidence that the low-affinity K+ transport system of Rhodobacter capsulatus is a uniporter. The effects of ammonium on the transporter

Comparison of the rate of accumulation of ⁸⁶Rb⁺ by intact cells of Rhodobacter capsulatus during short periods of illumination with the Rb⁺-dependent membrane ionic current measured by electrochromism supports the view that both activities reflect the operation of a low-affinity K⁺ transport system. In experiments performed under similar conditions the ratio of ⁸⁶Rb⁺ uptake to charge uptake was approx. 1.0, suggesting that the transport system operates as a uniporter. The addition of NH _inf4 ^sup+ to a cell suspension led to an increase in membrane ionic current but failed to inhibit the accumulation of ⁸⁶Rb⁺ during illumination. The presence of K⁺ and NH _inf4 ^sup+ inhibited the increase in cellular ATP levels at the onset of illumination. This effect was prevented by Cs⁺. The results are considered within the context of the hypothesis (Golby et al. Eur J Biochem 187: 589–597) that NH _inf4 ^sup+ can be transported by the K⁺ carrier and in the context of an alternative hypothesis that NH _inf4 ^sup+ increases the affinity of the K⁺ transport system for its natural substrate and for Rb⁺.Abbreviations pH pH difference across the cytoplasmic membrane - electrical potential difference across the cytoplasmic membrane