Presence of Cochlodinium catenatum (Gymnodiniales: Gymnodiniaceae) in red tides of Bahía de Banderas, Mexican Pacific

The evolution of an ichthiotoxic algal bloom caused by the dinoflagellate Cochlodinium catenatum was studied from July to December 2000. The abnormal multiplication of this dinoflagellate occurred in the form of a discoloration spreading between a temperature and salinity interval of 25-32 degrees C and 33-35 ups, respectively. The density of C. catenatum reached 10 841 cells ml(-1). The event was observed in large areas of Banderas Bay affecting 13 fish species, whose massive killing was due to suffocation (gill obstruction and excessive mucus production). The human population around the area did not present respiratory affections or skin irritation. The C. catenatum measurements suggest a hologamic and heterothalic reproduction. Their morphological characteristics suggest that C. polykrikoides, C. heterolobatum and C. catenatum are the same species. It is estimated that the species could be a recent introduction in the Mexican Pacific.     

Biochemical responses of fish exposed to a harmful dinoflagellate Cochlodinium polykrikoides

To elucidate the ichthyotoxic mechanisms of a harmful dinoflagellate Cochlodinium polykrikoides, biochemical responses of fish exposed to blooms were investigated. Particularly, based on our finding that oxidative damages of gill were associated with fish mortality (J. Plankton Res. 21 (1999) 2105-2115), dysfunction of ion-transporting enzymes and secretion of gill mucus of fish exposed to this bloom species were examined. The susceptibilities of several fishes to C. polykrikoides were different; the active pelagic fishes such as black scraper Thamnaconus septentrionalis, red sea bream Pagrus major, beakperch Oplegnathus fasciatus and seaperch Malakichthys wakiyae, were more vulnerable than the benthic fishes, flounder Paralichthys olivaceus and rockfish Sebastes inermis. In addition, the higher the algal cell density, the higher the fish mortality. When the test fishes were exposed to C. polykrikoides of 5000 cells ml(-1), the transport-related enzymes, carbonic anhydrase and Na(+)/K(+)-ATPase activities were significantly decreased. The activity of carbonic anhydrase was decreased with increasing algal cell density and exposure time. The quantity of total polysaccharide in gill mucus is higher in the fish exposed to C. polykrikoides than in the control fish; the magnitudes were higher in the pelagic fishes than that of benthic fishes. Moreover, a drop of blood pH and oxygen partial pressure (pO(2)) was also observed in red sea bream and flounder subjected to C. polykrikoides. These results suggest that the inactivation of gill transport-related enzymes activities, the fall in blood pO(2) and abnormal secretion of gill mucus by the C. polykrikoides may be one of the principal causes of fish kill.     

Possible factors responsible for the toxicity of Cochlodinium polykrikoides,a red tide phytoplankton

Cochlodinium polykrikoides, a harmful red tide dinoflagellate, is highly toxic to fish, but the toxic mechanism is still unknown. Recent study has suggested that C. polykrikoides generates reactive oxygen species (ROS) such as superoxide anion (O(2)(-)) and hydrogen peroxide (H(2)O(2)), and the ROS-mediated ichthyotoxicity has been proposed. In this study, we found that the levels of O(2)(-) and H(2)O(2) detected in C. polykrikoides were trace levels as compared with those of Chattonella marina which is well-known to produce ROS. Furthermore, no significant increase in O(2)(-) generation by C. polykrikoides was observed in the presence of lectins such as concanavalin A (Con A) and wheat germ agglutinin (WGA) or fish mucus prepared from skin and gill of yellowtail, whereas C. marina generated increased level of O(2)(-) responding to these stimuli. Interestingly, the cell-free aqueous extract prepared from C. polykrikoides showed toxic effect on the HeLa cells, but the extract of C. marina had no significant effect. Furthermore, gradual accumulation of polysaccharides in the medium was observed during the growth of C. polykrikoides, and the medium gradually became viscous, but no such changes were observed in the medium of C. marina. These results suggest that multiple factors may be responsible for the toxic mechanism of C. polykrikoides.     

Monitoring of algicidal bacterium, <Emphasis Type="Italic">Alteromonas</Emphasis> sp. Strain A14 in its application to natural <Emphasis Type="Italic">Cochlodinium polykrikoides</Emphasis> blooming seawater using fluorescence <Emphasis Type="Italic">in situ</Emphasis> hybridization

The red tide of dinoflagellate, Cochlodinium polykrikoides has frequently occurred in coastal waters, causing severe damage to fisheries. In the present study, the algicidal bacterium Alteromonas sp. A14 isolated from the southern coast of Korea was applied to a red tide of C. polykrikoides in a laboratory experiment. In the experiment, the abundance of the strain A14 was monitored using fluorescence in situ hybridization. Inoculation of the A14 at a final cell density of 9.0 x 10(5) cells/ml caused a significant decrease in C. polykrikoides abundance from 1,830 to 700 cells/ml during 2 days, while abundances of harmless diatoms rapidly increased from 3 days. Abundances of both A14 and other bacteria increased to 1 day. After 1 day, with flagellate abundance increased, bacterial abundance decreased. Finally, algicidal bacterial abundance decreased to 3.5 x 10(4) cells/ml. In the biological control of harmful algal blooms, in addition to decrease in target algal abundance and not occurrence of other harmful blooms, decrease in abundance of utilized organism is also important. This study emphasizes the importance of monitoring the inoculated bacterium when applying bacterium to natural seawater.     

Mixotrophy in the phototrophic harmful alga Cochlodinium polykrikoides (Dinophycean): prey species, the effects of prey concentration, and grazing impact

We first reported here that the harmful alga Cochlodinium polykrikoides, which had been previously known as an autotrophic dinoflagellate, was a mixotrophic species. We investigated the kinds of prey species and the effects of the prey concentration on the growth and ingestion rates of C. polykrikoides when feeding on an unidentified cryptophyte species (Equivalent Spherical Diameter, ESD = 5.6 microm). We also calculated grazing coefficients by combining field data on abundances of C. polykrikoides and co-occurring cryptophytes with laboratory data on ingestion rates obtained in the present study. Cocholdinium polykrikoides fed on prey cells by engulfing the prey through the sulcus. Among the phytoplankton prey offered, C. polykrikoides ingested small phytoplankton species that had ESD's < or = 11 microm (e.g. the prymnesiophyte Isochrysis galbana, an unidentified cryptophyte, the cryptophyte Rhodomonas salina, the raphidophyte Heterosigma akashiwo, and the dinoflagellate Amphidinium carterae). It did not feed on larger phytoplankton species that had ESD's > or = 12 microm (e.g. the dinoflagellates Heterocapsa triquetra, Prorocentrum minimum, Scrippsiella sp., Alexandrium tamarense, Prorocentrum micans, Gymnodinium catenatum, Akashiwo sanguinea, and Lingulodinium polyedrum). Specific growth rates of C. polykrikoides on a cryptophyte increased with increasing mean prey concentration, with saturation at a mean prey concentration of approximately 270 ng C ml(-1) (i.e. 15,900 cells ml(-1)). The maximum specific growth rate (mixotrophic growth) of C. polykrikoides on a cryptophyte was 0.324 d(-1), under a 14:10 h light-dark cycle of 50 microE m(-2) s(-1), while its growth rate (phototrophic growth) under the same light conditions without added prey was 0.166 d(-1). Maximum ingestion and clearance rates of C. polykrikoides on a cryptophyte were 0.16 ng C grazer(-1)d(-1) (9.4 cells grazer(-1)d(-1)) and 0.33 microl grazer(-1)h(-1), respectively. Calculated grazing coefficients by C. polykrikoides on cryptophytes were 0.001-0.745 h(-1) (i.e. 0.1-53% of cryptophyte populations were removed by a C. polykrikoides population in 1 h). The results of the present study suggest that C. polykrikoides sometimes has a considerable grazing impact on populations of cryptophytes.     

Harmful blooms of cyanobacteria (Oscillatoriaceae) and dinoflagellates (Gymnodiniaceae) in the Golfo de Nicoya, Costa Rica

Recently, the Pacific coast of Costa Rica has experienced an increase in both magnitude and frequency of harmful algae blooms (HAB). The lack of data regarding the dynamics of these events in the area, and the species of microalgae that produce them, are themes of great interest. The blooms have produced negative impacts on fishery resources and on human health in Costa Rica. In May 2002 a HAB left a large number of dead fish along the central Pacific coast. Water samples were collected using a phytoplankton net and fixed for subsequent processing by electron microscopy. In addition, a one liter sample of surface water was taken for later cell count. In the observed HAB, the dominating organisms found were the cyanobacteria Trichodesmiun erythraeum surrounded by high concentrations of Gram-bacteria and the dinoflagellate Cochlodinium cf. polykrikoides. T. erythraeum, is one of the most important N2 fixing cyanobacteria in marine waters that has been associated with HAB events in diverse parts of the world as well as with symptoms that produce contact dermatitis and other discomforts. C. cf. polykrikoides is a dinoflagellete associated with fish kills; although the type of associated toxins are unknown. In a national newspaper 17 cases of intoxication in humans were reported during this same period, which presented respiratory disorders and burning of the eyes. This is the first report in Costa Rica where a cyanobacteria and a dinoflagellate were observed together producing HAB.     

Cooccurrence of elevated urea levels and dinoflagellate blooms in temperate estuarine aquaculture ponds

In hybrid striped bass aquaculture ponds, dinoflagellate blooms were found on 10 of 14 occasions to co-occur with concentrations of urea in excess of 1.5 microM nitrogen. When urea levels were <1.5 microM nitrogen, on seven occasions, no evidence of dinoflagellate blooms was observed in these ponds.     

NO3-胁迫及恢复对黄瓜幼苗叶片叶绿素荧光参数及ATPase活性的影响

通过水培试验,探讨了不同NO₃^-浓度胁迫及恢复对黄瓜幼苗叶片叶绿素含量、叶绿素荧光参数及ATPase活性的影响.结果表明,胁迫7 d后,高浓度NO₃^-(168 mmol·L^-1)可极显著提高叶绿素a、叶绿素b、总叶绿素和类胡萝卜素含量,极显著提高初始荧光(F_o)、Mg ATPase和Ca-ATPase活性,而PSⅡ原初光能转化效率(F_v/F_m)、PSⅡ潜在活性(F_v/F_o)和PSⅡ光合电子传递量子效率(ΦPSⅡ),却随NO₃^-浓度的增加而降低.恢复7 d后,所有处理叶绿素和类胡萝卜素含量均低于对照;初始荧光基本都恢复至对照水平;PSⅡ原初光能转化效率和PSⅡ光合电子传递量子效率在NO₃^-浓度低于126 mmol·L^-1时,基本恢复至对照水平,而高于这一水平时,仍显著低于对照;PSⅡ潜在活性在NO₃^-浓度为42和126 mmol·L^-1的处理基本达对照水平,其它处理仍极显著低于对照;Mg-ATPase和Ca-ATPase活性均出现先降低后升高的变化趋势.     

Migratory benthic fishes may induce regime shifts in a tropical floodplain pond

1. Alternative states are a widely recorded phenomenon in shallow lakes, which may shift between turbid‐ and clear‐water conditions. Here, we investigate whether such shifts in a tropical floodplain pond may be related to the effect of the flood pulse regime on the community structures of fish and macrophytes. 2. Using a long‐term data set, we demonstrate how benthic fish migration together with colonisation by submerged plants affected the transition from a turbid to a macrophyte‐dominated state in a floodplain pond without top‐down control. 3. In our study, the turbid state occurred mostly during low water phases and was largely characterised by high values for the biomass of benthic fish, chlorophyll‐a and total phosphorous. 4. During the period of rising water levels, the migration of benthic fish out of the pond occurs simultaneously with the establishment of submerged plants, while water turbidity decreases along with phytoplankton and nutrient concentrations, inducing a clear‐water phase. However, when submerged plants are absent and fish migration is low, a transient state is generated. 5. We suggest that, in contrast to temperate ponds and shallow lakes, where the main driving mechanisms establishing alternative states are related to cascading effects via the food chain, in tropical ponds and shallow lakes it is resuspension of sediments by benthic fish that plays the most significant role in establishing alternative states. However, the effect of the flood pulse regime plays an important role in the temporal dynamics of fish community structure by controlling benthic fish migration.     

Diel and seasonal vertical distribution of meiobenthic copepods in muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay)

The vertical distribution of meiobenthic copepods was investigated within muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay, France). The aim of the study was to determine if in muddy sediments, as previously established in sandy sediments, meiobenthic copepods migrate vertically according to the seasons or diel periods. Two experimental approaches were used, viz: a three-season comparison was made of the diel vertical distribution of the harpacticoid Canuella perplexa T. & A. Scott (1893) and secondly the depth distribution of a meiobenthic copepod assemblage was followed for a 24 h period, in shallow water subtidal locations. The harpacticoid C. perplexa vertically migrated through the top three centimeters of the sediment, showing diel and seasonal variations in depth distribution. The differential vertical distributions shown by the dominant meiobenthic populations suggest that emergence into the water column may mainly concern surface dwelling copepods. The physical and biological factors affecting seasonal and diel changes in the copepod assemblage of the fish ponds are discussed.     

The loss of submerged plants with eutrophication I. Experimental design, water chemistry, aquatic plant and phytoplankton biomass in experiments carried out in ponds in the Norfolk Broadland

SUMMARY. 1 During eutrophication of shallow lakes, communities of submerged plants are often replaced by dense phytoplankton populations, but the mechanism by which this occurs is obscure though often assumed to involve shading. 2. This paper introduces a series investigating this change and describes a system of experimental ponds which were variously fertilized with nitrogen and phosphorus, had fish added or removed, and had their submerged aquatic plants cleared or left intact. 3. Fertilization with phosphate and ammonium nitrate in quantities effectively greater than those in a series of lakes in the adjacent Norfolk Broads, which have lost their submerged plants, did not displace the plant populations. 4. Total phosphorus and soluble reactive phosphorus concentrations in the water did not increase much with increasing loading in the presence of submerged plants but did so if the plants were manually cleared. Ammonium and nitrate concentrations were kept low, despite large additions in both plant dominated and manually cleared ponds. 5. In the absence of fish there were modest increases in chlorophyll a concentrations with phosphorus loading in the presence or absence of submerged plants. The concentrations achieved, however, were much lower than anticipated probably because of grazing by large-bodied Cladocera. 6. Ponds dominated by plants continued to have low phytoplankton populations even when fish were stocked. Low fish survival in these ponds permitted grazing zooplankters to flourish. In ponds cleared of plants, however, there were significant relationships between cholorophyll a concentration with Daphnia biomass (inverse) and log stock of potentially zooplanktivorous fish (positive). There was a significant relationship between chlorophyll a and total phosphorus concentrations in the plant and cleared ponds in 1982 but only in the plant ponds in 1983. In all cases the phytoplankton communities were dominated by small, often flagellated, organisms.     

Rapid monitoring for the potentially ichthyotoxic dinoflagellate Cochlodinium polykrikoides in Korean coastal waters using fluorescent probe tools

Cochlodinium polykrikoides has occurred annually in Korea’scoastal waters since 1982, where it has caused extensive fishmortality. Rapid and accurate monitoring is very important toreduce the economic damage caused by C. polykrikoides. However,before outbreaks of C. polykrikoides occur, single cells areoften more abundant than chain-forming cells. During this period,it is very difficult to discriminate C. polykrikoides from closelyrelated dinoflagellates and other phytoplankton species. Theaim of the present study was to identify even single-celledC. polykrikoides and to assess counting methodologies usingmolecular probes. A new polyclonal antibody bound specificallyto C. polykrikoides, and not to other phytoplankton, includingthe morphologically similar Gyrodinium impudicum and Gymnodiniumcatenatum. When cultured C. polykrikoides cells were fixed with2.5% glutaraldehyde, they emitted a high-intensity fluorescentsignal during the period of exponential growth. The correlationwith cell density of a mixed culture including C. polykrikoidestreated with an antibody and lectin probes (wheat germ agglutinin/Erythrinacristagalli agglutinin) was well matched (r² = 0.83). The detectionof C. polykrikoides was possible at concentrations as low as5 cells ml^-1. Reaction with C. polykrikoides antisera and antigenby western blotting analysis was at 30 kDa and gave no signalfor G. impudicum, G. catenatum, Alexandrium tamarense or Prorocentrummicans. Consequently, the new antibody is of great importancefor enumeration and identification of C. polykrikoides in Korea’swaters.     

Frameshift mutations induced by the acridine mustard ICR-191 in embryos and in the adult gill and hepatopancreas of rpsL transgenic zebrafish

To determine whether frameshift mutations can be detected in rpsL transgenic zebrafish (Brachydanio rerio), embryos, and adult fish were treated with 6-chloro-9-[3-(2-chloroethylamino)-propylamino]-2-methoxyacridine (ICR-191). Embryos exposed to 0, 10, or 20 microM ICR-191 in a water bath for 18 h exhibited induced mutant frequencies (MFs) of 14 x 10(-5), 16 x 10(-5), and 25 x 10(-5), respectively. Only embryos exposed to 20 microM ICR-191 showed a significant increase in MF. The mutational spectra differed between the control and ICR-191-treated groups and single G:C pair insertions, which are a marked characteristic of ICR-191 mutagenesis, were observed in both 10 and 20 microM-treated embryos. In adult fish treated with 1 microM ICR-191 in a water bath for 18 h, a significant increase in MFs was observed in both gill (12 x 10(-5) and 44 x 10(-5) in control and treated fish, respectively), and hepatopancreas (5 x 10(-5) and 29 x 10(-5), respectively) 2 weeks after exposure. Sequence analysis showed that 58% of mutations in gill and 94% of mutations in hepatopancreas were single G:C pair insertions, which is typical of mutations induced by ICR-191. Additionally, these mutations occurred predominantly at a single site (CC sequence at bps 140-141) in the rpsL gene. Three weeks after exposure, however, the increased MFs and prominent mutational spectra of ICR-treated fish were undetectable. These findings suggest that using our protocols the rpsL transgenic zebrafish mutation assay is more effective for adult fish than for embryos, but that frameshift mutations can be detected in both embryos and adults at appropriate sampling times after treatment with ICR-191.     

Remote sensing application for the study of rapid flushing to remediate eutrophication in shallow lagoons (Albufera of Valencia)

Albufera of Valencia shallow lagoon experiences water clarification about once a year. This study aimed to observe the timing of water clarity events and to detect the associated flow during these periods. Spatial variation in chlorophyll a along the Albufera was observed using remote sensing images. Due to the lagoon’s spatial complexity and the varying water qualities flowing in from more than 60 tributaries, remote sensing was the only approach that could obtain images simultaneously covering the entire lagoon. The data were used to explore the evolution, duration and intensity of the clear-water phase, and the lagoon’s subsequent re-eutrophication. The duration and intensity of the clear-water phase varied across the lagoon, but complete water quality renovation occurred in 1 week. Our analysis demonstrates that rapid flushing could remediate the lagoon eutrophication.

     

Total nitrogen oxide following exercise testing reflects endothelial function and discriminates health status

Nitric oxide (NO) bioavailability is important in vascular health, but unsuitable as a clinical measure due to biological oxidation. Total nitrogen oxides (NO(x)) are stable but background nitrate levels make it difficult to detect disease-based variation. We investigated the clinical discriminatory value of NO(x) as it relates to exercise capability (VO(2peak)) and brachial artery reactivity (BAR, an NO-dependent measure of endothelial health), in healthy (H), increased risk (RF), and known cardiovascular disease (CVD) subjects. BAR was measured using forearm occlusion/hyperemia stimulus. Subjects performed a maximal graded exercise test (GXT). Blood at rest, exercise termination, and 10 min into recovery was mixed equally with 0.1 M NaOH at 4 degrees C, filtered, and stored at -70 degrees C. NO(x) was measured by chemiluminescence. Seven of the RF group then exercise-trained for 6 months prior to retesting. The H group (n = 12) was younger, had higher VO(2peak), HDL levels, and baseline NO(x) values than the RF (n = 15) and CVD (n = 10) groups. NO(x) increased from baseline to recovery in the H group only (75.85 +/- 19.04 microM vs 97.76 +/- 31.93 microM; P 相似文献   

Summer algal communities and primary productivity in fish ponds

The paper presents data on primary productivity and phytoplankton communities in new experimental ponds which received the following treatments; ammonium nitrate and triplesuperphosphate, triplesuperphosphate, cracked corn (10% crude protein) and Auburn No. 3 fish feed (36% crude protein). Comparative data on algal communities were also obtained from production ponds which received feeds or fertilizers. Basic ecological data on macro-algae are also presented.

1. All nutrient additions to experimental ponds resulted in higher levels of gross photosynthesis and greater concentrations of chlorophyll a than were found in the control treatments. Fertilization with both nitrogen and phosphorus gave the highest values. Chlorophyll a and gross photosynthesis were higher in ponds receiving high protein content feed (Auburn No. 3) than in ponds to which low protein content feed (corn) was applied.
2. Persistent blooms of blue-green algae occurred in ponds receiving nitrogen and phosphorus fertilization. Phosphorus only fertilization produced blooms of blue-greens, but these blooms did not persist as in the ponds to which nitrogen was also added. Control ponds were dominated by green algae. Blue-green algae were seldom abundant in feed treatments.
3. Production ponds had high level of gross photosynthesis and large concentrations of chlorophyll a.
4. Many of the production ponds which received feed applications developed heavy blooms of blue-green algae.
5. The major species of blue-green algae observed in the present study were Oscillatoria sp., Raphidiopsis curvata, Anacystis nidulans, A. aeruginosa, Spirulina sp., and Anabaena circinalis. Heterocyst bearing forms, which can presumably fix nitrogen, were seldom noted in ponds that received continuous additions of nitrogen from fish feeds.
6. Macro-algae are abundant in many fish ponds. Data illustrating the competition of macro-algae with phytoplankton are presented.

     

Biphasic behavior of anammox regulated by nitrite and nitrate in an estuarine sediment

The production of N2 gas via anammox was investigated in sediment slurries at in situ NO2- concentrations in the presence and absence of NO3-. With single enrichment above 10 microM 14NO2- or 14NO3- and 15NH4+, anammox activity was always linear (P < 0.05), in agreement with previous findings. In contrast, anammox exhibited a range of activity below 10 microM NO2- or NO3-, including an elevated response at lower concentrations. With 100 microM NO3-, no significant transient accumulation of NO2- could be measured, and the starting concentration of NO2- could therefore be regulated. With dual enrichment (1 to 20 microM NO2- plus 100 microM NO3-), there was a pronounced nonlinear response in anammox activity. Maximal activity occurred between 2 and 5 microM NO2-, but the amplitude of this peak varied across the study (November 2003 to June 2004). Anammox accounted for as much as 82% of the NO2- added at 1 microM in November 2003 but only for 15% in May 2004 and for 26 and 5% of the NO2- added at 5 microM for these two months, respectively. Decreasing the concentration of NO3- but holding NO2- at 5 microM decreased the significance of anammox as a sink for NO2-. The behavior of anammox was explored by use of a simple anammox-denitrification model, and the concept of a biphasic system for anammox in estuarine sediments is proposed. Overall, anammox is likely to be regulated by the availability of NO3- and NO2- and the relative size or activity of the anammox population.     

Comparative culture and toxicity studies between the toxic dinoflagellate Pfiesteria piscicida and a morphologically similar cryptoperidiniopsoid dinoflagellate

A series of fish bioassays using cultures of the toxic dinoflagellate, Pfiesteria piscicida and a cryptoperidiniopsoid dinoflagellate indicated various degrees of toxicity for Pfiesteria piscicida and no toxicity by the cryptoperidiniopsoid. P. piscicida maintained toxicity in the presence of live fish, and this toxicity was perpetuated following a series of inoculations to other culture vessels. Differences in the onset and magnitude of the fish deaths occurred, requiring 16 days for the initial fish death when using P. piscicida from a culture that had previously been maintained on algal cells, to kills within hours when using a culture that had recently (previous day) killed fish. Autopsies of moribund fish from the test and control fish bioassays indicated a general lack of bacterial infection, which ensued following death of other autopsied fish. Moreover, bacterial comparisons of waters in the fish bioassay and control fish cultures indicated that similar bacterial concentrations were present. Neither oxygen or ammonia levels were determined to be factors in the fish death. Life stages of a cryptoperidiniopsoid dinoflagellate from Virginia estuaries were also identified, including motile zoospore, gametes, planozygote, amoebae, and cyst stages. The cryptoperidiniopsioid did not initiate fish deaths in bioassays conducted over a 14-week period at zoospore concentrations of ca. 700-800 cells ml(-1). Elemental X-ray analysis of the scales from cysts of this dinoflagellate and P. piscicida indicate that they both contain silicon. Overall, the data from this study demonstrate that the cryptoperidiniopsoid possesses several similar life stages and feeding patterns as P. piscicida, but was not toxic to fish.     

Dual effects of nitric oxide on cat carotid body chemoreception.

We studied the effects of nitric oxide (NO) released by NO donors on cat carotid body (CB) chemosensory activity during normoxia and hypoxia. CBs excised from pentobarbital sodium-anaesthetized cats were perfused with Tyrode at 38 degrees C and pH 7.40. The frequency of chemosensory discharges (f(x)) was recorded from the carotid sinus nerve, and changes of NO concentration were measured by a chronoamperometric technique, with NO-selective carbon-fiber microelectrodes inserted in the CB. During steady chemosensory excitation induced by hypoxia, bolus injections of NO (DeltaNO = 0. 5-12 microM), released by S-nitroso-N-acetylpenicillamine (SNAP) and 6-(2-hydroxy-1-methyl-nitrosohydrazino)-N-methyl-1-hexanamine++ + (NOC-9), transiently reduced f(x) in a dose-dependent manner. However, during normoxia, the same concentration of NO (DeltaNO = 0. 5-13 microM) released by the NO donors increased f(x) in a dose-dependent manner. The present results show a dual effect of NO on CB chemoreception that is dependent on the PO(2) levels. During hypoxia, NO is predominantly an inhibitor of chemoreception, whereas, in normoxia, NO increased f(x). The mechanisms by which NO produces chemosensory excitation during normoxia remain to be determined.     

Biosynthesis of nitric oxide and citrulline from L-arginine by constitutive nitric oxide synthase present in rabbit corpus cavernosum.

The objective of this study was to determine whether a constitutive isoform of nitric oxide (NO) synthase is present in rabbit corpus cavernosum that could account for the involvement of the L-arginine-NO pathway in neurogenically-elicited relaxation of the corpus cavernosum and, therefore, penile erection. Citrulline was determined by monitoring the formation of 3H-citrulline from 3H-L-arginine. NO was determined by monitoring the formation of total NO(x) (NO+nitrite [NO2-]+nitrate [NO3-]) by chemiluminescence after reduction of NO(x) to NO by acidic vanadium (III). Equimolar quantities of NO plus citrulline were generated from L-arginine and the formation of both products was time-dependent at 37 degrees C. NO synthase activity was distributed almost entirely to the cytosolic fraction. Enzymatic activity was completely dependent on NADPH, calmodulin, and calcium. Addition of tetrahydrobiopterin increased NO synthase activity by about 30 percent. The NO synthase inhibitor NG-nitro-L-arginine, abolished enzymatic activity. The Km for L-arginine was 17 microM and the Vmax of the reaction was 18 pmol/min/mg protein. These observations indicate that a cytosolic, constitutive isoform of NO synthase, like that found in brain neuronal tissue, is present in rabbit corpus cavernosum.