Biomedical subjects

Michael Kristensen

Publications and source records attributed to Michael Kristensen.

15 recordsLinked to original sources

PubMed2006

Variation of Musca domestica L. acetylcholinesterase in Danish housefly populations.

Anti-cholinesterase resistance is in many cases caused by modified acetylcholinesterase (MACE). A comparison was made of toxicological data and AChE activity gathered from 21 field populations and nine laboratory strains of houseflies, Musca domestica L., to elucidate the best way of generating data to provide advice for management strategies and gathering information for resistance risk assessment on the organophosphates azamethiphos and dimethoate and the carbamate methomyl, which have been the primary insecticides used against adult houseflies in Denmark. Cluster analysis was performed and > 2000 houseflies were assigned to one of three phenotypes based on total acetylcholinesterase activity as well as inhibition by azamethiphos, methomyl or omethoate. A cluster, i.e. a phenotype, with high total AChE activity and high sensitivity to azamethiphos and less sensitivity to inhibition by methomyl and omethoate was shown to be linked to methomyl resistance. It was not possible to define any clusters that could be linked to azamethiphos or dimethoate resistance. The five mutations V180L, G262A, G262V, F327Y and G365A causing anticholinesterase resistance in houseflies were all identified in the Danish housefly strains. The data are very heterogeneous, and a correlation of molecular genetic background and resistance of phenotypes is not obvious with the available data.

Acetylcholinesterase↗

PubMed2006

Survey of permethrin and malathion resistance in human head lice populations from Denmark.

Head lice, Pediculis capitis De Geer, populations were investigated for permethrin and malathion resistance after initial establishment of a discriminating dose of topical application bioassay with body lice, Pediculus humanus L. For both insecticides, approximately 2 times the lethal dose (LD)95 at 4 h was selected, 2 ng of permethrin and 100 ng of malathion per head louse, respectively. Head lice were collected from heads of infested children in Denmark at 33 primary schools, one kindergarten, and seven boarding schools. The lice were collected by combing of dry hair, with a fine-toothed antilouse comb attached to a vacuum cleaner. A resistance survey covers head lice collected from 208 of 1,441 persons combed. The frequency of permethrin- and malathion-resistant head lice is high in Danish head lice populations. In 17 of 24 samples tested for permethrin resistance, all head lice survived the discriminating dose. Six samples had between 3 and 25% dead head lice, whereas one sample had 60% mortality. In nine of 25 samples tested for malathion resistance, all head lice survived the discriminating dose. Seven samples had <25% dead head lice, and four samples had a mortality of 50% or more at the discriminating dose. The connection between permethrin resistance and kdr-like mutations is confirmed by our findings. The frequency of the double mutation T929I-L932 F in the voltage-sensitive sodium channel gene associated with permethrin resistance was 0.95 in Danish head lice populations.

Adolescent↗

PubMed2005

Membrane proteins involved in potassium shifts during muscle activity and fatigue.

Muscle activity is associated with potassium displacements, which may cause fatigue. It was reported previously that the density of the large-conductance Ca2+-dependent K+ (BK(Ca)) channel is higher in the T tubule membrane than in the sarcolemmal membrane and that the opposite is the case for the ATP-sensitive K+ (K(ATP)) channel. In the present experiments, we investigated the subcellular localizations of the strong inward rectifier 2.1 K+ (Kir2.1) channel and the Na+-K+-2Cl- (NKCC)1 cotransporter with Western blot analysis of different muscle fractions. Furthermore, muscle function was studied while trying to manipulate the opening probability or transport capacity of these proteins during electrical stimulation of isolated soleus muscles. All experiments were made with excised muscle from male Wistar rats. Kir2.1 channels were almost undetectable in the sarcolemmal membrane but present in the T tubule membrane, whereas NKCC1 cotransporters were present in the sarcolemmal membrane. For muscles incubated in a buffer containing pinacidil, NS1619, Ba2+, or bumetanide, there was a faster reduction in peak force (P < 0.05). Furthermore, bumetanide incubation reduced the peak force at the onset of electrical stimulation (P < 0.05). Thus the effects on muscle force indicate that these drugs can affect K+-transporting proteins and thereby influence K+ accumulation, especially in the T tubules, suggesting that K(ATP) and BK(Ca) channels are responsible for K+ release and decrease in force during repeated muscle contractions, whereas Kir2.1 and NKCC1 may have a role in K+ reuptake.

Animals↗

PubMed2005

Correlation of a resistance-associated Rdl mutation in the German cockroach, Blattella germanica (L), with persistent dieldrin resistance in two Danish field populations.

Danish Blattella germanica (L) populations carry the resistance-associated mutation A302S within the Resistance to dieldrin (Rdl) gene. The mutation has remained in field populations long after the discontinuation of dieldrin for cockroach control. The mutation has also persisted in our laboratory strains with high and intermediate frequencies for more than 8 years without selection. The toxicity of dieldrin was tested by topical application to male cockroaches in the susceptible strain DPIL-SUS and two field strains, Zo960302 and Su960304, which were 1270- and 15-fold resistant to dieldrin at LD50. We report the sequencing of exon 7 of the B. germanica Rdl gene and the finding of the putative resistance-associated A302S mutation. We have developed and implemented a PCR-based diagnostic method with the detection of a restriction endonuclease polymorphism, which allows for easy discrimination of susceptible, resistant and heterozygote genotypes. The frequency of the resistance-associate allele A302S was 0.97 and 0.38 in the Zo960302 and Su960304 populations, respectively. The cockroach Rdl A302S allele confers high dieldrin resistance in homozygotes and intermediate resistance in heterozygotes, and its presence is responsible for the persisting dieldrin resistance in Danish populations of B. germanica.

Amino Acid Sequence↗

PubMed2005

Identification of sodium channel mutations in human head louse (Anoplura: Pediculidae) from Denmark.

The presence of the two mutations T9291-L932F in the voltage-sensitive sodium channel gene associated with permethrin resistance (kdr-like) was shown in head louse, Pediculus humanus capitis De Geer, populations in Denmark. The existence of one susceptible and one T929I-L932F haplotype based on the limited single nucleotide polymorphism (SNP) of these sequences was established. One louse had an SNP causing a G943A substitution in the trans-membrane segment five of domain II on the sodium channel, which has not been identified in other insect species. A polymerase chain reaction-restriction endonuclease method using genomic DNA to discriminate between resistant and susceptible alleles in head lice was developed and implemented. The SNP that results in the T9291 substitution also creates a cutting site for the restriction endonuclease SspI, and the presence of one or two SspI cutting sites in head lice is diagnostic for the T9291-L932F haplotype.

Amino Acid Sequence↗

PubMed2005

Cross-resistance between dieldrin and fipronil in German cockroach (Dictyoptera: Blattellidae).

The toxicity of fipronil and dieldrin was determined in one susceptible laboratory strain and seven insecticide-resistant field-collected strains of Blattella germanica (L). The Zo960302 and Ga021001 strains were 1,270- and 2,030-fold resistant to dieldrin and 15- and 14-fold resistant to fipronil. The Su960304 and Od010803 strains were 15- and 13-fold resistant to dieldrin and two- and four-fold resistant to fipronil. Three strains showed no or a low level of resistance to dieldrin and fipronil. Crosses were performed between the susceptible strain Danish Pest Infestation Laboratory (DPIL)-SUS and the resistant strains Zo960302 and Su960304 and resistance to dieldrin and fipronil were intermediate compared with the susceptible and the resistant strains. Backcrosses to both of the parental strains showed cosegregation of dieldrin and fipronil resistance. The toxicity of dieldrin and fipronil was correlated when compared at LD50, and 93% of the observed variation in LD50 of fipronil can be ascribed to variation among predictions based on the value of LD50 of dieldrin. The frequency of the A302S substitution in the resistance to dieldrin (Rdl) gene in the highly dieldrin- and fipronil-resistant strains Zo960302 and Ga021001 and the moderately resistant Su960304 was 0.97, 1.0, and 0.38, respectively. We consider the connection between the frequency of the Rdl mutation and dieldrin and fipronil resistance a causal connection and not merely a coincidence.

Animals↗

PubMed2005

Glutathione S-transferase and insecticide resistance in laboratory strains and field populations of Musca domestica.

Glutathione S-transferase (GST) activity of 10 house fly laboratory strains and 21 field populations are described with two substrates, 1-chloro-2,4-dinitrobenzene (CDNB) and 3,4-dichloronitrobenzene (DCNB), commonly associated with resistance. Three laboratory strains selected by tetrachlorvinphos, lindane (gamma-HCH) and dimethoate, respectively, had significantly elevated CDNB- and DCNB-GST activities. The multiresistant field population 791a had significantly elevated CDNB- and DCNB-GST activities. Many strains recorded several individuals with high CDNB- and/or DCNB-GST activity and to evaluate these differences, phenotypes were defined by cluster analysis. A phenotype, GST-R, indicating high CDNB- and DCNB-GST activities, was found in 23 of 31 laboratory strains or field populations. GST-R was likely to be involved in gamma-HCH resistance in strain 17e, tetrachlorvinphos resistance in strain 39m2b, and dimethoate resistance in strain 49r2b. The frequency of GST-R in selected laboratory strains and field population correlated with the frequency of house flies surviving the organophosphate azamethiphos either topically applied or by ingestion. There was no significant correlation between GST activity and the toxicity of the organophosphate dimethoate or the pyrethroids bioresmethrin and pyrethrin.

Animals↗

PubMed2004

Lactate and force production in skeletal muscle.

Lactic acid accumulation is generally believed to be involved in muscle fatigue. However, one study reported that in rat soleus muscle (in vitro), with force depressed by high external K(+) concentrations a subsequent incubation with lactic acid restores force and thereby protects against fatigue. However, incubation with 20 mm lactic acid reduces the pH gradient across the sarcolemma, whereas the gradient is increased during muscle activity. Furthermore, unlike active muscle the Na(+)-K(+) pump is not activated. We therefore hypothesized that lactic acid does not protect against fatigue in active muscle. Three incubation solutions were used: 20 mM Na-lactate (which acidifies internal pH), 12 mM Na-lactate +8 mm lactic acid (which mimics the pH changes during muscle activity), and 20 mM lactic acid (which acidifies external pH more than internal pH). All three solutions improved force in K(+)-depressed rat soleus muscle. The pH regulation associated with lactate incubation accelerated the Na(+)-K(+) pump. To study whether the protective effect of lactate/lactic acid is a general mechanism, we stimulated muscles to fatigue with and without pre-incubation. None of the incubation solutions improved force development in repetitively stimulated muscle (Na-lactate had a negative effect). It is concluded that although lactate/lactic acid incubation regains force in K(+)-depressed resting muscle, a similar incubation has no or a negative effect on force development in active muscle. It is suggested that the difference between the two situations is that lactate/lactic acid removes the negative consequences of an unusual large depolarization in the K(+)-treated passive muscle, whereas the depolarization is less pronounced in active muscle.

Animals↗

PubMed2004

Cross-resistance potential of fipronil in Musca domestica.

The toxicity of fipronil to insecticide-susceptible houseflies and the cross-resistance potential of fipronil were determined for six insecticide-resistant laboratory housefly strains by topical application and feeding bioassay. The insecticide-resistant strains represented different levels and patterns of resistance to pyrethroids, organophosphates, carbamates and organochlorines. Five strains were almost susceptible to fipronil in feeding bioassay with resistance factors at LC50 between 0.36 and 3.0. Four of these strains were almost susceptible to topically applied fipronil (resistance factors at LD50 were 0.55, 0.83, 3.3 and 2.5, respectively), whereas one strain was 13-fold resistant to topically applied fipronil. A highly gamma-HCH-resistant strain, 17e, was 430-fold resistant to fipronil in topical application bioassay and 23-fold resistant in feeding bioassay at LD50/LC50. We also tested the toxicity of fipronil in a feeding bioassay and gamma-HCH in topical application bioassay on thirteen housefly field populations. Eleven of the field populations had resistance factors for fipronil ranging from 0.98 to 2.4 at LC50, whereas two populations were 4.0- and 4.6-fold resistant to fipronil. The resistance level to gamma-HCH at LD50 in the field populations ranged from 1.8- to 8.1-fold. The two strains showing fipronil resistance were 3.4- and 8.1-fold resistant to gamma-HCH. Fipronil and gamma-HCH toxicities were positively correlated in the field populations. Biochemical assays of esterase, glutathione S-transferase and cytochrome P450 monooxygenase indicated that the low fipronil resistance observed in laboratory and field strains could be caused by elevated detoxification or be due to a target-site resistance mechanism with cross-resistance to gamma-HCH.

Animals↗

PubMed2004

Frequency of kdr gene in house fly field populations: correlation of pyrethroid resistance and kdr frequency.

The frequency of the L1014 F kdr mutation was determined in 14 field populations of house flies, Musca domestica L., with resistance factors at LD50 for pyrethrin/piperonyl butoxide and bioresmethrin/piperonyl butoxide from 4 to 29 and 2 to 98, respectively. A polymerase chain reaction test for identifying kdr homo- or heterozygote house flies was used to determine the frequency of kdr. The L1014 F allele was found in all populations tested. The frequency of kdr in the field populations was high and varied from 0.46 to 0.99. Eleven of the populations were in Hardy-Weinberg equilibrium, whereas two strains had higher number of heterozygotes than expected, indicating a possible heterozygote advantage. The frequency of kdr was strongly correlated with the reduced mortality observed in the bioassays with pyrethrum and bioresmethrin synergized by piperonyl butoxide. This indicates that kdr is a major mechanism for pyrethroid resistance in these field populations. Five field populations had resistance factors >25 and >10 for bioresmethrin/piperonyl butoxide and pyrethrin/piperonyl butoxide, respectively. The frequencies of kdr in these five populations varied from 0.89 to 0.99. The frequencies of kdr in the field populations showing no or a low level of resistance had frequencies of kdr from 0.46 to 0.75, which indicates that the L1014 F kdr allele is a fully recessive genetic trait in house flies. We have shown that the molecular diagnostic PASA method to determine the resistance phenotypes and the frequency of kdr is a powerful tool, which could be used to get information to make recommendations about pest and resistance management.

Alleles↗

PubMed2004

Susceptibility of spinosad in Musca domestica (Diptera: Muscidae) field populations.

The toxicity of spinosad was determined in one susceptible and five insecticide-resistant laboratory strains of house fly, Musca domestica L. Spinosad was relatively slow-acting, but highly toxic to house flies. In a feeding bioassay, spinosad LC50 at 72 h was 0.51 microg of spinosad per gram of sugar, making it 6.3- and 3.5-fold more toxic to house flies compared with azamethiphos and methomyl, respectively. In topical application bioassay, the LD50 at 48 h of spinosad in susceptible house flies was 40 ng per 20 mg of house fly, making spinosad less toxic than the pyrethroid bioresmethrin synergized by piperonyl butoxide and the organophosphate dimethoate. The insecticide-resistant laboratory strains had resistance factors to spinosad at LC50 in feeding bioassay from 1.5 to 5.5 and at LD50 in topical application bioassay from 2.5 to 4.7, indicating that in house fly cross-resistance to the major insecticide classes will not initially be of major concern for the use of spinosad for house fly control. The toxicity of spinosad was also evaluated against 31 field populations of house flies collected from livestock farms across Denmark. The field populations were 2.2- to 7.5-fold resistant to spinosad at 72 h in feeding bioassay, but based on steep slopes in the bioassay and the limited variation of spinosad toxicity against the various field populations, we consider the field populations to be spinosad-susceptible. We propose a diagnostic dose of 12 microg of spinosad per gram of sugar in feeding bioassay with impregnated sugar for determination of resistant house flies, which is 10x the LC95 of the susceptible strain WHO and approximately = 2x the LD95 of the field populations. Spinosad showed no substantial cross-resistance to the pyrethroid bioresmethrin synergized by piperonyl butoxide, the anticholinesterases dimethoate, azamethiphos, methomyl, and spinosad in house fly field populations.

Animals↗

PubMed2004

Statistical analyses of repeated measures in physiological research: a tutorial.

Experimental designs involving repeated measurements on experimental units are widely used in physiological research. Often, relatively many consecutive observations on each experimental unit are involved and the data may be quite nonlinear. Yet evidently, one of the most commonly used statistical methods for dealing with such data sets in physiological research is the repeated-measurements ANOVA model. The problem herewith is that it is not well suited for data sets with many consecutive measurements; it does not deal with nonlinear features of the data, and the interpretability of the model may be low. The use of inappropriate statistical models increases the likelihood of drawing wrong conclusions. The aim of this article is to illustrate, for a reasonably typical repeated-measurements data set, how fundamental assumptions of the repeated-measurements ANOVA model are inappropriate and how researchers may benefit from adopting different modeling approaches using a variety of different kinds of models. We emphasize intuitive ideas rather than mathematical rigor. We illustrate how such models represent alternatives that 1) can have much higher interpretability, 2) are more likely to meet underlying assumptions, 3) provide better fitted models, and 4) are readily implemented in widely distributed software products.

Animals↗

PubMed2003

Effects of high-intensity intermittent training on potassium kinetics and performance in human skeletal muscle.

A rise in extracellular potassium concentration in human skeletal muscle may play an important role in development of fatigue during intense exercise. The aim of the present study was to examine the effect of intense intermittent training on muscle interstitial potassium kinetics and its relationship to the density of Na(+),K(+)-ATPase subunits and K(ATP) channels, as well as exercise performance, in human skeletal muscle. Six male subjects performed intense one-legged knee-extensor training for 7 weeks. On separate days the trained leg (TL) and the control leg (CL) performed a 30 min exercise period of 30 W and an incremental test to exhaustion. At frequent intervals during the exercise periods interstitial potassium ([K(+)](I)) was determined by microdialysis, femoral arterial and venous blood samples were drawn and thigh blood flow was measured. Time to fatigue for TL was 28% longer (P < 0.05) than for CL (10.6 +/- 0.7 (mean +/-s.e.m.) versus 8.2 +/- 0.7 min). The amounts of Na(+),K(+)-ATPase alpha(1) and alpha(2) subunits were, respectively, 29.0 +/- 8.4 and 15.1 +/- 2.7% higher (P < 0.05) in TL than in CL, while the amounts of beta(1) subunits and ATP-dependent K(+) (K(ATP)) channels were the same. In CL [K(+)](I) increased more rapidly and was higher (P < 0.05) throughout the 30 W exercise bout, as well at 60 and 70 W, compared to TL, whereas [K(+)](I) was similar at the point of fatigue (9.9 +/- 0.7 and 9.1 +/- 0.5 mmol l(-1), respectively). During the 30 W exercise bouts and at 70 W during the incremental exercise femoral venous potassium concentration ([K(+)](v)) was higher (P < 0.05) in CL than in TL, but identical at exhaustion (6.2 +/- 0.2 mmol l(-1)). Release of potassium to the blood was not different in the two legs. The present data demonstrated that intense intermittent training reduce accumulation of potassium in human skeletal muscle interstitium during exercise, probably through a larger re-uptake of potassium due to greater activity of the muscle Na(+),K(+)-ATPase pumps. The lower accumulation of potassium in muscle interstitium in the trained leg was associated with delayed fatigue during intense exercise, supporting the hypothesis that interstitial potassium accumulation is involved in the development of fatigue.

Adenosine Triphosphate↗

PubMed2003

Larvicide resistance in Musca domestica (Diptera: Muscidae) populations in Denmark and establishment of resistant laboratory strains.

We determined the toxicity of the two IGRs, diflubenzuron and cyromazine, in this survey of resistance in Danish field populations of Musca domestica (L.). We observed resistance toward diflubenzuron and for the first time in Denmark and we found field populations with some resistance to cyromazine. Eleven of the twenty-one field populations had larvae surviving a diagnostic dose of 1.6 times of susceptible LC95 of diflubenzuron and two of these populations had larvae surviving 6.1 times of LC95. Eight of the twenty-one field populations had larvae surviving 2.2 times of susceptible LC95 of cyromazine and one population had larvae surviving 4.4 times of LC95. A fivefold cyromazine resistant strain was established after selection with cyromazine. It was 3-, 5-, and 90-fold resistant to diflubenzuron, triflumuron, and methoprene, respectively. Two diflubenzuron resistant strains (120- and 86-fold, respectively) were established. They showed a high level of resistance to triflumuron (1000- and 200-fold, respectively), and moderate resistance to methoprene (73- and 50-fold, respectively). Both were susceptible to cyromazine. This study shows that by applying the recommendations of previous resistance risk assessments, severe control failures and detrimental development of a high level of resistance have been avoided. The development of resistance has not been completely avoided, but has not developed to a level of biological or economic importance.

Animals↗

PubMed2002

Localization and function of ATP-sensitive potassium channels in human skeletal muscle.

The present study investigated the localization of ATP-sensitive K+ (KATP) channels in human skeletal muscle and the functional importance of these channels for human muscle K+ distribution at rest and during muscle activity. Membrane fractionation based on the giant vesicle technique or the sucrose-gradient technique in combination with Western blotting demonstrated that the KATP channels are mainly located in the sarcolemma. This localization was confirmed by immunohistochemical measurements. With the microdialysis technique, it was demonstrated that local application of the KATP channel inhibitor glibenclamide reduced (P < 0.05) interstitial K+ at rest from approximately 4.5 to 4.0 mM, whereas the concentration in the control leg remained constant. Glibenclamide had no effect on the interstitial K+ accumulation during knee-extensor exercise at a power output of 60 W. In contrast to in vitro conditions, the present study demonstrated that under in vivo conditions the KATP channels are active at rest and contribute to the accumulation of interstitial K+.

Adenosine Triphosphate↗