Performance and seasonal abundance of the neotropical brown stink bug, shape Euschistus heros nymphs and adults on a novel food plant (pigeonpea) and soybean

Pigeonpea, Cajanus cajan (L.) Millsp. (Leguminosae) was found as a novel food plant of the neotropical brown stink bug, Euschistus heros (F.), in Paraná State, Brazil. Laboratory studies indicated nymphs performing better when fed on immature pods of soybean, Glycine max (L.) Merrill (Leguminosae), than on immature pods of pigeonpea. Female nymphs required 1.7 d less to complete development and tended to have a lower mortality on soybean (17.5%) than on pigeonpea (25.0%). At emergence, fresh body weight was greater on soybean than on pigeonpea. Adult E. heros performed better on soybean than on pigeonpea. After 120 d, 35% of adults were alive on soybean and 30% on pigeonpea; 93.3% of females oviposited on soybean, and 73.3% on pigeonpea, with an oviposition delay of 17 days on pigeonpea compared to soybean. Fecundity was 63% greater on soybean than on pigeonpea, and adult body weight gain for females and males at different ages was 6–36% greater on soybean than on pigeonpea. E. heros colonized soybean during January–March, from the pod-setting and filling stages (R3–R6) to maturity (R7–R8), and pigeonpea during April–June. These results indicate that E. heros has expanded its host range to pigeonpea in Brazil; pods of this plant are suitable food, and can support the insect during autumn-early winter, after soybean harvest, and before it enters into partial hibernation.     

Dispersal patterns of endemic alpine butterflies with contrasting population structures:<Emphasis Type="Italic"> Erebia epiphron</Emphasis> and<Emphasis Type="Italic"> E. sudetica</Emphasis>

We studied population sizes and mobility of Erebia epiphron and Erebia sudetica, two high mountain butterflies forming endemic subspecies in the Hrubý Jeseník Mountains, Czech Republic. E. epiphron formed two continuous populations containing 100,000 and 4,500 individuals on alpine grasslands. The butterflies moved freely within their habitats, but movements between the two populations were highly unlikely. E. sudetica formed a system of colonies at timberline sites on valley headwalls and in forest clearings. Two such colonies studied in detail contained 4,500 and 450 adults and were interconnected by limited dispersal. The negative exponential function and the sigmoid function (this assumes flat decrease of movements over short distances) were superior to the inverse power function in fitting mobility data for both species. For E. sudetica, the functions describing movements within a habitat differed significantly from total movements, suggesting different behaviours of dispersing individuals. The habitats of E. epiphron are uniform and highly isolated, favouring free within-habitat mobility but prohibiting leaving their boundaries. The habitats of E. sudetica are diverse and disturbance-dependent; leaving such habitats is less risky, and a source-sink model may explain the persistence of the species in the mountains.     

Effects of exogenous linoleic acid on fatty acid composition,receptor-mediated cAMP formation,and transport functions in rat astrocytes in primary culture

We have examined the effects of culturing neonatal rat-brain astrocytes in medium containing delipidated serum, with or without added linoleic acid (LA, 18:26), on membrane fatty-acid composition and functions. After 18–21 days in culture, polyunsaturated fatty acids (PUFA) constituted24 mol% of the total fatty acids in the astrocytes grown in delipidated media (controls); these proportions were increased by 35–40% to33 mol% when the cells were supplemented with 35M LA. Notable differences in the PUFA profiles of the cells cultured with or without added LA included: (a) higher proportions of 6 PUFA in the LA-supplemented astrocytes (25%, relative to10% in controls) that were accompanied by an increase in the ratio of 6/3 PUFA (from <2 in controls to 5), and (b) higher proportions of 20:39 and 22:39 in the control astrocytes (>5%) relative to the LA-supplemented cells (1%). The major metabolites in the 6 PUFA-enriched cells were arachidonic (20:46), adrenic (22:46) and docosapentaenoic (22:56) acids (15, 5 & 3 mol%, respectively). Enrichment of the astrocytes in 6 PUFA did not alter basal levels of cAMP, nor did it affect the amounts of cAMP formed in response to forskolin, isoproterenol, adenosine or histamine. However, dopamine-dependent increases in cAMP formation in the presence of the phosphodiesterase inhibitor, Ro 20-1724, were reduced by 25% relative to those in controls. LA supplementation modified uptake of [³H]adenosine into the astrocytes; values for K_t for a high affinity transport were increased relative to controls, and maximum capacity of a lower affinity process was reduced. Uptake of [³H]glutamate was not altered in the 6 PUFA-enriched astrocytes. This study demonstrated that cultured astrocytes take up exogenous linoleic acid and incorporate its metabolites into, phospholipid, and that the resulting changes in membrans PUFA composition modify only specific cell functional properties.Abbreviations PUFA polyunsaturated fatty acid(s) - EFA essential fatty acid(s) - LA linoleic acid - AA arachidonic acid - DHA docosahexaenoic acid - BSA bovine serum albumin - DMEM Dulbecco's modified Eagle's medium - TBARS thiobarbituric-acid-reactive substances - NECA 5-N-ethylcarboxamidoadenosine Special issue dedicated to Dr. Leon S. Wolfe.     

Studies of the protein content of individualPergamasus longicornis (Berlese) (Acari: Mesostigmata: Parasitidae)

The protein content ofPergamasus longicornis (Berlese) individuals is of the order of 45 g bovine serum albumen equivalents and varies depending on gender, time of year and gut colour (postulated nutritive state). Variation between males and females closely matches their size difference. A sinusoidal relationship with a late spring/early summer maximum and a late autumn/early winter minimum is shown for females. Gut colour is a useful predictor in females only. Pregnancy and prey utilisation over the year are suggested as important determinants of protein content and are discussed in detail.     

Vorläufige Versuche über die Elastizität des Atraktoplasmas

Summary Spindles of nuclei mostly from metaphases of expiants in vitro, Set free according to Dan's method by means of solutions of Duponol (a sodium lauryl sulfonate), have been studied according to their elasticity. The isolated atractoplasm has shown a static modul of elasticityE0.8 to 1.6×10⁶ dynes×cm^–2, and, sometimes, a Poisson number of0.42, that is to say the atractoplasmic gel of the spindles of nuclei is certain elastically. The values of the modul of elongation agree satisfactory with those values recently ascertained by Crick and Hughes with cytoplasm oi explanted cells.     

Mutational spectrum induced in Saccharomyces cerevisiae by the carcinogen N-2-acetylaminofluorene

The spectrum of mutations induced by the carcinogen N-2-acetylaminofluorene (AAF) was analysed in Saccharomyces cerevisiae using a forward mutation assay, namely the inactivation of the URA3 gene. The URA3 gene, carried on a yeast/bacterial shuttle vector, was randomly modified in vitro using N-acetoxy-N-2-acetylaminofluorene (N-AcO-AAF) as a model reactive metabolite of the carcinogen AAF. The binding spectrum of AAF to the URA3 gene was determined and found to be essentially random, as all guanine residues reacted about equally well with N-AcO-AAF. Independent Ura^– mutants were selected in vivo after transformation of the modified plasmid into a ura3 yeast strain. Plasmid survival decreased as a function of AAF modification, leading to one lethal hit (37% relative survival) for an average of 50 AAF adducts per plasmid molecule. At this level of modification the mutation frequency was equal to 70 × 10^–4, i.e. 50-fold above the background mutation frequency. UV irradiation of the yeast cells did not further stimulate the mutagenic response, indicating the lack of an SOS-like mutagenic response in yeast. Sequence analysis of the URA3 mutants revealed 48% frameshifts, 44% base substitutions and 8 % complex events. While most base substitutions (74%) were found to be targeted at G residues where AAF is known to form covalent C8 adducts, frameshift mutations were observed at GC base pairs in only 24% of cases. Indeed, more than 60% of frameshift events occurred at sequences such as 5-(A/T)_nG-3 where a short (n = 2 or 3) monotonous run of As or Ts is located on the 5' side of a guanine residue. We refer to these mutations as semi-targeted events and present a potential mechanism that explains their occurrence.     

Second-derivative Fourier transform infrared spectra of seaweed galactans

The Fourier transform infrared spectra of agar, agarose, -, -, and -carrageenan, and ofChondrus canaliculatus, Iridaea ciliata, I. membranacea, I. laminarioides andGracilaria chilensis polysaccharides were recorded in the 4000–400 cm^-1 region. The bands in the second derivative mode are sharper and more bands are resolved than in the normal spectra.Agar, agarose andG. chilensis phycocolloids exhibit diagnostic bands at 790 and 713 cm^-1. -, - and -carrageenans, and native carrageenan-type polysaccharides fromC. canaliculatus andIridaea species exhibit bands at around 1160, 1140, 1100, 1070, 1040, 1008, 610, and 580 cm^-1. Therefore, FT-IR spectroscopy in the second-derivative mode may be applied to differentiate between agar- and carrageenan-types seaweed galactans.     

Stable carbon isotope ratios for the gray whale (<Emphasis Type="Italic">Eschrichtius robustus</Emphasis>) in the breeding grounds of Baja California Sur,Mexico

This work investigated the feeding ecology and behaviour of gray whales in Bahía Magdalena. Underwater observations of bottom feeding were made (n=4). Skin biopsies of the gray whale had a carbon isotope value of –16.5 ± 0.1 (range from –16.4 to –16.7, n=7). Prey in Bahía Magdalena had a carbon isotope value of –18.4. Dietary enrichment from prey in Bahía Magdalena would correspond to 2 ± 0.1, whereas previously published results for prey in Alaska would result in an enrichment of 3, which suggests that whales were more likely feeding on prey from Bahía Magdalena. Carbon isotopic oscillation along the baleen plate of a stranded 1-year-old whale showed a variation in diet during the year, which suggests continual feeding during this time and corresponding to dietary sample measurements from Bahía Magdalena in winter and Alaska in summer.     

Feeding and diel vertical migration cycles of Metridia gerlachei (Giesbrecht) in coastal waters of the Antarctic Peninsula

Diel vertical migration and feeding cycles of adult female Metridia gerlachei in the upper 290 m of a 335-m water column were measured during a total of 65 h in two periods of early summer (Dec 20–21 and Dec 25–26, 1991). Samples collected in eight depth strata by 35 MOCNESS tows (333-m mesh) were analyzed for abundance and mean individual gut pigment content. Most of the copepod population was concentrated in a 50-m depth interval at all times. Feeding began simultaneously with nocturnal ascent from a depth of 200–250 m at 18:00 h (local time), when the relative change in ambient light intensity was greatest. Ingestion rate increased exponentially (k_i = 0.988 h^–1) at double the gut evacuation rate (k_e = 0.488 h^–1) as the population moved upward at 22.3–26.5 m h^–1 through increasing concentrations of particulate chlorophyll-a. Although the bulk of the population did not move to depths shallower than 50 m, and began its downward migration at a rate of 20.8–31.7 mh^–1 in complete darkness, individual females continued to make brief excursions into chlorophyll-rich surface waters (4–8 g l^–1) during the first few hours of population descent. Ingestion rate diminished abruptly by one order of magnitude (k_i = 0.068 h^–1) at dawn ( 0330 h). Within four more hours, the population had reached its daytime depth and gut pigment content remained constant at a minimum value until the next migration cycle. No feeding appeared to take place at depth during the day. Ingestion by M. gerlachei females removed < 4% of daily primary production, with only 20% of this amount being removed from surface waters by active vertical transport.     

The nucleotide sequence of the mitochondrial DNA molecule of the grey seal,Halichoerus grypus,and a comparison with mitochondrial sequences of other true seals

The sequence of the mtDNA of the grey seal, Halichoerus grypus, was determined. The length of the molecule was 16,797 base pairs. The organization of the molecule conformed with that of other eutherian mammals but the control region was unusually long due to the presence of two types of repeated motifs. The grey seal and the previously reported harbor seal, Phoca vitulina, belong to different but closely related genera of family Phocidae, true (or earless) seals. In order to determine the degree of differences that may occur between mtDNAs of closely related mammalian genera, the 2 rRNA genes, the 13 peptide coding genes, and the 22 tRNA genes of the 2 species were compared. Total nucleotide difference in the peptide coding genes was 2.0–6.1%. The range of conservative difference was 0.0–1.5%. In the inferred peptide sequences the amino acid difference was 0.0–4.5%, and the difference with respect to chemical properties of amino acids was 0.0–3.0%. A gene that showed a limited degree of difference in one mode of comparison did not necessarily show a corresponding limited difference in another mode. The ratio for differences in codon positions 1, 2, and 3 was 2.7:1:16. The corresponding ratio for conservative differences was 1.8:1. l:1. The evolutionary separation of the two species was calculated to have taken place 2–2.5 million years ago. This dating gives the figure 8 × 10^–9 as the mean rate of substitution per site and year in the entire mtDNA molecule. Comparison with the cytochrome b gene of the Hawaiian monk seal and the Weddell seal suggested that the lineage of these two species and that of the grey and harbor seals separated 8 million years ago. Correspondence to: Ú. Árnason     

Volume-dependent regulation of sodium and potassium fluxes in cultured vascular smooth muscle cells: Dependence on medium osmolality and regulation by signalling systems

Summary To identify ion transport systems involved in the maintenance of vascular smooth muscle cell volume the effects of incubation medium osmolality and ion transport inhibitors on the volume and ⁸⁶Rb and ²²Na transport in cultured smooth muscle cells from rat aorta (VSMC) have been studied. A decrease of medium osmolality from 605 to 180 mosm increased intracellular water volume from 0.6 to 1.3 l per 10⁶ cells. Under isosmotic conditions, cell volume was decreased by ouabain (by 10%, P< 0.005) but was not influenced by bumetanide, furosemide, EIPA and quinidine. These latter compounds were also ineffective in cell volume regulation under hypotonic buffer conditions. Under hyperosmotic conditions, cell volume was decreased by bumetanide (by 7%, P<0.05) and by ethylisopropyl amiloride (by 13%, P< 0.005). Ouabain-sensitive ⁸⁶Rb influx was decreased by 30–40% under hypoosmotic conditions. An increase in medium osmolality from 275 to 410 mosm resulted in an eightfold increase in bumetanide-inhibited ⁸⁶Rb influx and ⁸⁶Rb efflux. The (ouabain and bumetanide)-insensitive component of ⁸⁶Rb influx was not dependent on the osmolality of the incubation medium. However (ouabain and bumetanide)-insensitive ⁸⁶Rb efflux was increased by 1.5–2 fold in VSMC incubated in hypotonic medium. Ethylisopropyl amiloride-inhibited ²²Na influx was increased by sixfold following osmotic-shrinkage of VSMC. The data show that both Na⁺/H⁺ exchange and Na⁺/K⁺/2Cl^– cotransport may play a major role in the regulatory volume increase in VSMC. Basal and shrinkage-induced activities of Na⁺/K⁺/2Cl^– cotransport in VSMC were similarly sensitive to inhibition by either staurosporin, forskolin, R24571 or 2-nitro4-carboxyphenyl N,N-diphenylcarbomate (NCDC). In contrast basal and shrinkage-induced Na⁺/K⁺/2Cl^– cotransport were differentially inhibited by NaF (by 30 and 65%, respectively), suggesting an involvement of guanine nucleotide binding proteins in the volume-sensitive activity of this carrier. Neither staurosporin, forskolin, R24571 nor NCDC influenced shrinkage-induced Na⁺/H⁺ exchange activity. NaF increased Na⁺/H⁺ exchanger activity under both isosmotic and hyperosmotic conditions. These data demonstrate that different intracellular signalling mechanisms are involved in the volume-dependent activation of the Na⁺/K⁺/2Cl^– cotransporter and the Na⁺/H⁺ exchanger.The authors gratefully acknowledge the financial support of the Swiss National Foundation, grant No. 3.817.087. Bernadette Weber is thanked for preparing the figures.     

Patterns of Fish Movement on Eastern Tasmanian Rocky Reefs

We assessed small-scale movement patterns of fishes on three eastern Tasmanian reefs by divers visually resighting 1040 individuals of 16 species marked with unique colour-coded tags. With the possible exception of the monacanthid Acanthaluteres vittiger, common species showed high fidelity to site, with individuals generally resighted <100m from the initial tagging site and remaining near the tagging site throughout the 1 year duration of study. The wrasses Pictilabrus laticlavius and Notolabrus tetricus were more sedentary than Notolabrus fucicola and the monacanthids Meuschenia australis and Meuschenia freycineti. Body length, sex, water temperature and time since tagging had little influence on distance moved compared to variation between individuals, other than movement distance increasing with body length for N. tetricus. Movement patterns were generally consistent at all three sites, although mean distance moved by N. fucicola was double at Swanport and Return Point compared to Lobster Point. N. tetricus but not P. laticlavius emigrated from areas artificially cleared of macroalgae. The sedentary nature of most small- to medium-sized reef fish species, particularly labrids, indicates that relatively small (1km diameter) marine protected areas should generally provide conservation benefits for these fishes but few `spillover' benefits in surrounding areas.     

Larval development and food habits of the marbled parrotfish, <Emphasis Type="Italic">Leptoscarus vaigiensis</Emphasis>, associated with drifting algae

The larval development and food habits of the marbled parrotfish, Leptoscarus vaigiensis (Scaridae) associated with drifting algae were studied. In this study, 628 L. vaigiensis of various developmental stages ranging from postflexion larvae (9.4mm in standard length, SL) to adults (192.0mmSL) were sampled from drifting algae at two fishing ports in Nakagusuku Bay of Okinawa Island. In 3969 fish comprising 65 taxa in 34 families of Teleostei collected with drifting algae, L. vaigiensis occupied 15.8% of samples and occurred generally throughout the whole year. A large number of L. vaigiensis were collected from July to October accompanied by an occurrence of drifting algae composed of Sargassum spp. Larvae and early juveniles ranging from 11.1 to 14.9mmSL appeared sporadically throughout the year, and postflexion larvae 11mmSL occurred from July to November. Their food shifted from planktonic copepods in postflexion larvae and juveniles ranging from 10.0 to 14.9mmSL to seaweed in the juveniles ranging from 15.0 to 24.9mmSL. Furthermore, adults and young over 25mmSL fed almost exclusively on seaweed, with Sargassum spp. constituting the drifting algae. These facts indicate that drifting algae may have a role concerning food and habitat, and may act as a nursery for L. vaigiensis.     

Influence of sex, age and season on the feeding habits of the flatfish Solea senegalensis

Synopsis The Senegal sole Solea senegalensis is a commercially valuable fish and it is beginning to be cultured, in an extensive way, in fish farms in southern European countries. Little is known about its feeding habits, unlike other Solea species such as the common sole Solea solea. This paper studies the feeding habits of a wild population of Senegal sole. Differences according to sex, age and season were statistically analyzed. A total of 376 fish, aged between two and six years old, were studied over a single year. Twenty eight different families of prey were identified, belonging, in order of abundance, to crustaceans, polychaetes and molluscs. The Senegal sole trophic profile (preys items with a Simpson's dominance index 2) was: Glyceridae, Nephtydidae, Onuphidae, Apseudidae, Ampeliscidae and Upogebiidae. Feeding habits of Senegal sole were significantly influenced by sex, age and season, with crustaceans being the prey most affected.This paper is dedicated to the memory of Daniel Ray Ogilvie. who died 7 January 1995.     

A simple urea leaf-feeding method for the production of 13C and 15N labelled plant material

The use of ¹³C isotope tracer techniques in terrestrial ecology has been restricted by the technical requirements and high costs associated with the production of ¹³C enriched plant material by ¹³CO₂ release in labelling chambers. We describe a novel, simple and relatively inexpensive method for the small-scale production of ¹³C and ¹⁵N labelled plant material. The method is based on foliar feeding of plants with a urea solution (97 atom% ¹³C, 2 atom% ¹⁵N) by daily misting. Maize was grown in a greenhouse in a compost–soil mixture and enclosed in clear polythene bags between urea applications. Final enrichment in 27 d old maize shoots was 211 ¹³C (1.34 atom% ¹³C) and 434 ¹⁵N (0.52 atom% ¹⁵N). Enrichments of hot-water extractable fractions (289 ¹³C, 469 ¹⁵N) were only slightly higher than those observed in plant bulk material, which suggests that daily urea applications ensured fairly uniform labelling of different biochemical fractions and plant tissues. Recovery of applied excess ¹³C and ¹⁵N in plant shoots was 22% and 42%, respectively. Roots were less enriched (21 ¹³C and 277 ¹⁵N), but no attempts were made to recover roots quantitatively.     

Some notes on the ecology of a GermanBranchipus schaefferi population (Crustacea: Anostraca)

Habitat preference, seasonal occurrence, starvation resistance, hatching eggs ofBranchipus schaefferi, and effects of predation onB. schaefferi were studied.Branchipus was only present in turbid, unvegetated ponds and absent in ponds which contain higher aquatic vegetation and theSpirogyra sp. The first individuals ofB. schaefferi appeared in April when water temperature was 10 °C and the last adults in November at a water temperature of 3.5 °C. Up to 6 reproducing generations were observed during this period. Abundance ofB. schaefferi was higher in temporary ponds than in permanent ponds. Sex ratio was close to unity for most of the year. Body size ofB. schaefferi males and females was significantly positively correlated with pond volume. Without foodB. schaefferi could survive for 1.5 to 2 days at 20 °C and 4 to 5 days at 10 °C. Hatching success of eggs decreased when eggs were dried for 7 months. Freezing of eggs had no effect on hatching success. From] the predators tested,Chaoborus sp. larvae clearly selected smallB. schaefferi; one consumed approximately 6Branchipus d–1 at a density of 6 to 12 prey 1–1. The other predators, dragonfly larvae, and larvae and adults ofTriturus alpestris selected alternative prey types, for exampleTubifex sp. and ostracods.     

Pattern and timing of evolutionary divergences among hominoids based on analyses of complete mtDNAs

We have examined and dated primate divergences by applying a newly established molecular/paleontological reference, the evolutionary separation between artiodactyls and cetaceans anchored at 60 million years before present (MYBP). Owing to the morphological transformations coinciding with the transition from terrestrial to aquatic (marine) life and the large body size of the animals (which makes their fossils easier to find), this reference can be defined, paleontologically, within much narrower time limits compared to any local primate calibration marker hitherto applied for dating hominoid divergences. Application of the artiodactyl/cetacean reference (A/C-60) suggests that hominoid divergences took place much earlier than has been concluded previously. According to a homogenous-rate model of sequence evolution, the primary hominoid divergence, i.e., that between the families Hylobatidae (gibbons) and Hominidae, was dated at 36 MYBP. The corresponding dating for the divergence betweenPongo (orangutan) andGorilla-Pan (chimpanzee)-Homo is 24.5 MYBP, that forGorilla vsHomo-Pan is 18 MYBP, and that forHomo vsPan 13.5 MYBP. The split between Sumatran and Bornean orangutans was dated at 10.5 MYBP and that between the common and pygmy chimpanzees at 7 MYBP. Analyses of a single gene (cytochromeb) suggest that the divergence within the Catarrhini, i.e., between Hominoidea and Old World monkeys (Cercopithecoidea), took place >40 MYBP; that within the Anthropoidea, i.e., between Catarrhini and Platyrrhini (New World monkeys), >60 MYBP; and that between Anthropoidea and Prosimii (lemur), 80 MYBP. These separation times are about two times more ancient than those applied previously as references for the dating of hominoid divergences. The present findings automatically imply a much slower evolution in hominoid DNA (both mitochondrial and nuclear) than commonly recognized.     

Model predictions of the ionic mechanisms underlying the beating and bursting pacemaker characteristics of molluscan neurons

The general properties of the excitable membrane on molluscan pacemaker neurons can be described on the basis of a fair amount of experimental evidence available in the literature. The neuronal membrane exhibits under voltage clamp an initial inward current carried by both Na⁺ and Ca²⁺ ions, the time- and voltage-dependent characteristics of which are similar to that of other excitable structures. The conductance mechanism for the two ion species and the transport kinetics appear to be closely similar. The time course and amplitude of the delayed outward current carried by K⁺ ions shows a marked dependence on the membrane potential. Characteristic for the molluscan neurons is the existence of an additional fast transient outward current which is only activated by hyperpolarizing shifts from the membrane potential. A regular beating discharge over a wide range of frequencies can be predicted by making the assumption of a metabolically controlled driving of the Na⁺ conductance. Bursting pacemaker characteristics can be correctly simulated by the model if sinusoidal variations of an additional Na⁺ and Ca²⁺ conductances g _Na and g _Ca, and periodic variations of the K⁺ conductance g _K, governed by the known operation of a metabolic substrate cycle are introduced. The close approximation of experimentally observed impulse bursts requires that the actual inpulse-frequency and the amplitude of the after-spike hyperpolarization are determined by the temporal pattern of g _Na, while the spike amplitude is controlled by g _Na which (although of similar time course) is lagging in phase behing g _Na. The periodic changes in additional K⁺ conductance g _K, are responsible for burst termination and the changes in inter-burst interval, to the effect that spike doublets, triplets and multi-spike bursts can be simulated by a suitable choice for the time characteristics of g _K. The model makes use of the finding that the Ca²⁺ inflow associated with a spike discharge actually activates g _K, so that large postburst hyperpolarizations can be obtained in high-frequency bursts.Supported by the Deutsche Forschungsgemeinschaft (Grant Ch 25/1)     

A note on the kinetics of uptake of d-glucose by the food yeast,Candida utilis

Unlike other yeasts so far investigated, the d-glucose carrier of Candida utilis (strain NCYC 737) appears to change affinity for d-glucose according to its exogenous concentration. When the concentration of d-glucose was <0.4 mM, the apparent K _m 0.2 mM; at >0.4 mM, the K _m 10 mM.     

Amplification and latency in photoreceptors: Integrated or separated phenomena?

It is shown that the models for the transduction process in photoreceptors which treat latency and amplification as integrated phenomena (integrated models) yield time scales for single photon signals (quantum bumps) which distinctly conflict with the experimentally observed ones for the ventral nerve photoreceptor of Limulus: the ratio of bump duration/ latency t _B/t _lat is predicted by integrated models to be 3 in contrast to the experimental result of 0.5. Moreover, integrated models lead to a predicted value of an extinction rate of 50%, i.e., 50% of the absorbed photons should be expected to cause no signal in the dark adapted state of the cell. In this paper it is shown that separation of latency and amplification in such a way that the latency causing process precedes amplification in the transduction process eliminates these discrepancies. In addition, the separate modeling of latency and amplification resolves the rather large ambiguity in determining the exponent n of the initial signal current J(t) ⁿreported in the literature to be between n2 (from noise analysis) up to n17 (from flash experiments). Two alternative models for the latency part of transduction are suggested which give a qualitatively much better agreement with the experimental histograms of latencies.List of Symbols A quantum bump amplitude, maximum of quantum bump signal current - latency criterion as a fraction in terms of J _max - E energy of the stimulating flash - g conductance of a single light-regulated channel - I(t) light intensity of the stimulating flash as a function of time - J(t) response current of photoreceptors to light flashes under voltage clamp - J _max maximum signal current response signal - J _min minimum current above which the signal current becomes distinguishable from the base line noise - k rate constant in models separating latency from amplification - L ligand in ligand binding model - rate constant of exponential bump decay - m number of amplification steps following gainless latency process in models separating latency and amplification - n exponent in the initial behaviour J(t)t ⁿ - Q net charge transfer of quantum bump signal current - (t) first-passage time probability density - t _B duration of quantum bump response - t _lat latency time - t _max time to peak for quantum bumps - t _r rise time for quantum bumps - U U-U _L, U=clamp voltage, U _L=reversal potential of light-regulated channels - v amplification factor - X _k intermediate conformations in transduction models This work was supported by Deutsche Forschungsgemeinschaft (SFB 160)