The limiting effect of dichloroacetate on endotoxin-induced liver damage in starved rats

Dichloroacetate has been shown to have therapeutic effects on sepsis and endotoxin shock and to reduce liver damage in rats intoxicated with ethanol or carbon tetrachloride. In this study, the effect of dichloroacetate on endotoxin hepatitis was investigated. Endotoxin hepatitis was induced by an intraperitoneal coadministration of 50 micrograms/kg lipopolysaccharide from Escherichia coli, and 200 mg/kg D-galactosamine in starved, male Wistar rats. This treatment induced the following changes within 24 hr: an increase in the serum aminotransferase activity, histological alterations of the liver including focal necrosis of liver cells and inflammatory infiltrates, an increase in blood pyruvate and alanine concentrations, and inhibition of starvation ketosis. The intraperitoneal administration of 250 mg/kg dichloroacetate 30 min after the administration of the toxins partially counteracted all of these changes. The administration of dichloroacetate might be useful in coping with hepatic damage as well as lacticemia and cardiovascular depression induced by endotoxins.

Low-Km aldehyde dehydrogenase deficiency does not influence the elevation of blood pressure by alcohol

Increased alcohol consumption causes hypertension and leads to higher death rates by hemorrhagic strokes. About half of the Japanese population have inactive low Km aldehyde dehydrogenase (ALDH2), which metabolizes acetaldehyde to acetic acid at very low concentrations, leading to severe pharmacological effects of aldehyde when drinking alcohol. We determined persons with inactive ALDH2 using a ethanol patch test. All male workers (n + 163), aged from 21 to 62 years in one factory in Japan took part. They were divided into two groups by alcohol consumption (nondrinkers, light drinkers of < 32 ml/l ethanol per day and moderate to heavy drinkers of > or = 32 ml ethanol per day). The prevalence of persons with inactive ALDH2 was 52.1%. The prevalence of moderate to heavy drinkers among persons with inactive ALDH2 was significantly lower than that among those with active ALDH2 (23% and 41%, respectively: P < 0.05). No significant differences of BP were observed between ALDH2 inactive and active groups at the same consumption of alcohol. This study showed a significant relationship between categories of alcohol use and SBP and DBP (P < 0.05, respectively) controlled for age and body mass index. The mechanism by which alcohol use elevates BP is unlikely to be related to the inactive ALDH2. However, inactive ALDH2 may act as a protective factor against hypertension by reducing alcohol consumption.

Carbon tetrachloride increases sinusoidal efflux of reduced and oxidized glutathione in rats

To elucidate the significance of the changes in plasma glutathione concentrations associated with carbon tetrachloride (CCl4)-induced liver damage, the changes in the concentrations of reduced (GSH) and oxidized glutathione (GSSG) in plasma as well as in the liver were investigated in rats. In the liver, the concentration of GSH decreased, and that of GSSG increased 24 hr after the intraperitoneal administration of CCl4. In the right atrial plasma, the concentration of both GSH and GSSG increased. The GSH/GSSG ratio in the plasma decreased as did that in the liver. The net sinusoidal efflux of GSH and GSSG from the liver was calculated by subtracting their concentrations in plasma of the infrahepatic inferior vena cava from those of the suprahepatic inferior vena cava. The net efflux of GSH and GSSG started to increase as early as 3-6 hr after CCl4 administration, and reached a plateau 6 and 24 hr after CCl4 administration, respectively. On the other hand, an elongation of prothrombin time and leakage of alanine aminotransferase reached a maximum 24 and 48 hr after CCl4 administration, respectively. Vacuolization in the centri-lobular region and inflammatory infiltration started 3 and 6 hr after CCl4 administration, respectively, and progressed for 48 hr. These results suggest that CCl4 induced an increase in plasma concentrations of GSH as well as GSSG by increasing their efflux from the liver, and that the changes in plasma glutathione status might be a useful and sensitive marker for CCl4-induced liver damage.

[Prediction of prognosis of patients with gastrointestinal cancer based on thymidine uptake]

In 173 patients with operable gastric cancer and in 127 patients with colorectal cancer, the relations between thymidine uptake by cancer cells in semi-solid media, their clinico-pathologic features and survival times, were studied. Multivariate analysis using Cox proportional hazard model showed that thymidine uptake is one of the variables most highly correlated with the probability of patient death. Thus, the availability of thymidine uptake information in the perioperative period may be useful for selecting patients who would benefit from more intensive therapy. Thymidine kinase (TK) is the only enzyme by which thymidine is introduced into the DNA metabolism. In 64 specimens, including gastric and colorectal cancers, TK levels in the serum and tumors were measured accordingly. However, there was no correlation between thymidine uptake and the TK levels, suggesting the necessity of measuring thymidine phosphorylase activity as well.

FTIR spectral study of intramolecular hydrogen bonding in thromboxane A2 receptor agonist (U-46619), prostaglandin (PG)E2, PGD2, PGF2 alpha, prostacyclin receptor agonist (carbacyclin), and their related compounds in dilute CCl4 solution: structure-activity relationships

FTIR spectra measurements and full optimization curve analysis of their spectra were done to obtain parameters of the OH and C = O stretching vibration bands for intramolecular hydrogen bondings in thromboxane (TX)A2 receptor partial agonist (CTA2), prostaglandin (PG)E2, PGD2, PGF2 alpha, prostacyclin (PGI2) receptor agonist (carbacyclin), and their related compounds in dilute CCl4 solutions. For CTA2, PGE2, PGD2, and PGF2 alpha, cyclic intramolecular hydrogen bonds involving a 15-membered ring similar to that observed for the TXA2 receptor agonist (U-46619) were found between a carboxyl group of the alpha-side chain and a 15-hydroxyl group of the omega-side chain. The arrangement of these side chains was P-shaped, and the percentage of the intramolecular hydrogen-bonded molecules with the 15-membered ring in CCl4 solution showed a high value of ca. 80% for these compounds. In addition, it was found that the cyclic intramolecular hydrogen bonds involving the 13-, 12-, and 12-membered rings in PGE2, PGD2, and PGF2 alpha, respectively, are formed between the carboxyl group of the alpha-side chain and the 11-, 9-, and 9-hydroxyl groups of a cyclopentane ring, respectively, although the percentages of the intramolecular hydrogen-bonded molecules with these membered rings are very small. It was also found that the hydrogen bond is more easily formed in the order of the 11-, 9-, and 15-hydroxyl groups. For carbacyclin, the cyclic intramolecular hydrogen bond involving the 13-membered ring was found between the carboxyl group of the alpha-side chain and the 11-hydroxyl group. The percentage of the intramolecular hydrogen-bonded molecules showed the value of 58% for carbacyclin. On the basis of information on the side-chain conformations in CCl4, we examined the structure-activity relationships for U-46619 in place of TXA2, PGE2, PGD2, PGF2 alpha, and carbacyclin in place of PGI2.

The effects of dichloroacetate on liver damage and circulating fuels in rats exposed to carbon tetrachloride

It has been known that carbon tetrachloride-induced liver damage in starved rats is ameliorated simply by restoration of feeding. An analogue of dichloroacetate has been reported to ameliorate carbon tetrachloride-induced liver damage, and dichloroacetate has been shown to have a variety of effects on fuel metabolism. We investigated simultaneously the effects of dichloroacetate on liver damage and on circulating fuels in rats exposed to carbon tetrachloride. The effects of carbon tetrachloride varied with the rat's condition. In starved rats, the liver damage was more severe, and serum ketone body concentration decreased. In non-starved rats, the liver damage was not as severe and the serum ketone body concentration increased. The administration of dichloroacetate ameliorated liver damage both in starved and in non-starved rats given carbon tetrachloride: the administration of dichloroacetate protected from the liver damage particularly in starved rats. There were associated changes in the concentrations of circulating fuels. When the pyruvate-lowering effect of dichloroacetate was diminished in carbon tetrachloride-injected, starved rats, the alanine aminotransferase-lowering effect of dichloroacetate was also diminished. We propose that dichloroacetate's effect on fuel metabolism may produce a hepato-protective effect.

Increase in the plasma concentration of reduced glutathione observed in rats with liver damage induced by lipopolysaccharide/D-galactosamine: effects of ulinastatin, a urinary trypsin inhibitor

The changes in plasma concentrations of reduced glutathione were investigated in rats with endotoxin hepatitis. An increase in serum alanine aminotransferase activity and in serum total bilirubin concentration was observed 12 hr after the intraperitoneal co-administration of small doses of Escherichia coli lipopolysaccharide and D-galactosamine in starved rats. At the same time, an increase in the plasma concentration of reduced glutathione was also observed. The increase in reduced glutathione from 14 +/- 2 to 20 +/- 9 microM (n = 11, P < 0.05) correlated well with that in serum alanine aminotransferase activity. Ulinastatin, a potent inhibitor of polymorphonuclear leukocyte elastase, partially counteracted all of these changes. Ulinastatin also reduced histological liver damage induced by endotoxin. We conclude that the increase in the plasma concentration of reduced glutathione reflects hepatocellular damage associated with endotoxin hepatitis. The partial reversal of the damage by ulinastatin is consistent with the proposal that the activation of polymorphonuclear leukocytes is involved in endotoxin hepatitis.

Changes in total serum cholesterol and other risk factors for cardiovascular disease in Japan 1980-1989

To monitor recent changes in Japan in diet and risk factors for cardiovascular disease (CVD), in the light of the decline on coronary heart disease, total serum cholesterol levels and other risk factors were compared between two nationwide health surveys in 1980 and 1989 conducted in the same population as the annual National Nutrition Surveys. Between 1980 and 1989, age-adjusted total serum cholesterol levels increased from 4.84 to 5.22 for men and from 4.91 to 5.24 mmol/l for women. Prevalence of age-adjusted hypercholesterolaemia of > or = 5.68 mmol/l (220 mg/dl) increased from 15.8% to 29.4% for men and from 18.4% to 30.6% for women. Decline in blood pressure was observed for both sexes. Prevalence of smoking decreased from 64.7% to 58.7% in men while prevalence in women remained low (from 10.1 to 9.9%). Considerable increases in total serum cholesterol levels do not offer an explanation of the recent decline in mortality from coronary heart disease in Japan. This may, in part, be related to a decline in blood pressure levels.

Hypertriglyceridemia and lowered apolipoprotein C-II/C-III ratio in uremia: effect of a fibric acid, clinofibrate

We examined the effects of a fibric acid, clinofibrate, on lipoprotein metabolism in 12 hyperlipidemic patients with uremia treated on continuous ambulatory peritoneal dialysis during a 24 week treatment. Daily dose of clinofibrate was 200 mg for the initial four weeks, 400 mg for the second four weeks, and 600 mg for the subsequent 16 weeks. Serum and very-low density lipoprotein (VLDL) triglyceride were decreased by 36% and 48%, respectively. Neither total cholesterol nor apolipoprotein B changed significantly, whereas cholesterol was decreased in VLDL and increased in low (LDL) and high density lipoprotein (HDL) fractions. Post-heparin plasma lipoprotein lipase (LPL) before treatment was not lower than the normal value, and we found no change in LPL activity following clinofibrate. Hepatic triglyceride lipase also did not change. Apolipoprotein (apo) C-II/C-III ratio was low as compared to the normal value before treatment, and the ratio was increased by 38% after the treatment. Decrease in VLDL triglyceride was associated with increase in apo C-II/C-III ratio in all the cases. Abnormal enrichment with triglyceride of LDL and HDL fractions was improved by clinofibrate. Although one patient had a transient and asymptomatic elevation of serum creatine phosphokinase, no patient had muscle pain. There was no accumulation of the drug in the 24 week trial. These results suggest that clinofibrate is an effective and safe approach to the management of dyslipidemia in CAPD patients.

[Factors influencing self-registration in a bone-marrow bank: analysis of data from a population survey in Shiga Prefecture]

A population survey of awareness and attitudes regarding a bone-marrow bank was carried out in 19 cities and towns of Shiga prefecture in July 1991, to identify factors that would promote donor self-registration among the general population. The survey involved 832 residents (416 men and 416 women) selected as follows: Each social welfare commissioner of the cities and towns selected a total of eight residents, one male and one female from each of 4 age groups (20-29, 30-39, 40-49 and 50-59 years old). The questionnaires were distributed and collected by the social welfare commissioners with an overall response rate of 97.4%. Subjects answered questions regarding their experience and desire to participate in social volunteer activities, knowledge about bone-marrow banks, their perception of it's necessity, and whether they would participate in a bone-marrow bank, etc. A total of 25.9% of male and 20.6% of female subjects stated they had a desire to register in a bone-marrow bank. From the result of multiple regression analysis, the characteristics of those who showed interest in registration in a bone-marrow bank included having heard of the bone-marrow bank, experience in social volunteer activity, experience in blood donation, knowledge of bone-marrow transplantation and living in a town where need for establishment of a bone-marrow bank was widely discussed among residents. In the promotion of the idea of a bone-marrow bank, the role of motivating people to participate in voluntary blood donation and other social volunteer activities appears to be important.(ABSTRACT TRUNCATED AT 250 WORDS)

[A comparative study of the health conditions of elderly people living alone, elderly couples and the bedridden elderly at home in a rural area of Shiga Prefecture: special reference to morbidity rate and blood pressure, electrocardiograph and blood examination data]

For the purpose of obtaining basic data and for establishing a support system for elderly people with various health and social problems, a population survey was performed in 1990 to investigate the health and living conditions of elderly people living alone, elderly couples and the bedridden elderly in the town of Shigaraki, Shiga Prefecture. A total of 275 subjects (103 male, 172 female) 65 years of age and over were surveyed. The participation rate in this survey was 88.1%. Analysis of health conditions (morbidity rate, blood pressure, electrocardiograph and blood examination data) of elderly people living alone, elderly couples and the bedridden elderly produced the following: 1) Stroke was the main cause of being bedridden in men, while in women, bone and joint disease, especially fracture, was the main cause. 2) The combined prevalence of hypertension and borderline hypertension in elderly people living alone, elderly couples and the bedridden elderly was over 50%. The bedridden elderly had a lower prevalence than elderly people living alone and elderly couples. 3) Men in all of the above mentioned life styles, had a higher tendency of showing ECG abnormalities than women. The tendency for major ECG abnormalities was high for bedridden elderly, both male and female, with the tendency for men being higher. 4) In bedridden elderly, a tendency of higher prevalence of anemia, in both male and females, lower total serum cholesterol and triglyceride in males compared to elderly people living alone and in elderly couples, was observed.

Role of the integument in insect immunity: epicuticular abrasion and induction of cecropin synthesis in cuticular epithelial cells

When the epicuticle of a silkworm larva, Bombyx mori, was lightly abraded in the presence of live Bacillus licheniformis, Enterobacter cloacae, or bacterial cell wall components, cecropin mRNAs were detected in the underlying epithelial cells and in fat body cells remote from the abraded area. Antibacterial activity due to cecropin was detected in the matrix of the lightly abraded cuticle but not in nonabraded portions of the cuticular matrix or in the hemolymph surrounding the fat body, unless a more severe cuticular abrasion was administered. A light abrasion to a larva of the giant silkworm moth, Hyalophora cecropia, in the presence of E. cloacae also induced antibacterial activity in the abraded cuticle. These data illustrate that the ectodermally derived lepidopteran larval integument, when challenged by live bacteria or their cell wall components, mounts an immune response. Hence, the insect exoskeleton, which is often considered as an inert protective armor, is indeed actively participating in defense.

[A study on interleukin-6 in inflammatory bowel disease]

The production of interleukin-6 (IL-6) in patients with inflammatory bowel disease (IBD) has been measured, including the effects of steroid hormone, salicylazosulfapyridine (SASP) and its metabolites. In active Crohn's disease (CD) (n = 12) and ulcerative colitis (UC) (n = 9), rate of IL-6 positive group in serum was significantly higher than that in controls (n = 20) (p < 0.01, p < 0.01). In active CD (n = 9) and UC (n = 9), the level of IL-6 production by peripheral blood mononuclear cells (PBMNC) was 22.8 +/- 15.1 ng/ml, 24.3 +/- 14.4 ng/ml, and it was significantly higher than that in controls (n = 15, 8.0 +/- 6.6 ng/ml) (p < 0.05, p < 0.01). IL-6 production by PBMNC always showed the time dependent increase both in IBD and controls, and the level of IL-6 was always higher in IBD than that in controls during the culture time. Furthermore, IL-6 production by monocyte in UC (n = 6, 4.4 +/- 1.4 ng/ml) was significantly higher than that in controls (n = 6, 1.7 +/- 0.8 ng/ml) (p < 0.01). The effects of steroid hormone, SASP and its metabolites on IL-6 production were also investigated. Steroid hormone significantly reduced IL-6 production by PBMNC, but others had no effect on IL-6 production. This study suggested that IL-6 might be involved in the pathophysiology of IBD.

Dendritic cells in esophageal cancer and lymph node tissues

The density of infiltrating S-100 protein-positive dendritic cells (DCs) on histological sections and that of CD1- and L-M2 positive DCs on cryostat sections of esophageal dysplastic and cancerous lesions were examined. There was no significant correlation between the number of S-100 protein-positive DCs and the degree of dysplasia, tumor of S-100 protein-positive DCs and the degree of dysplasia, tumor differentiation, depth of invasion or lymph node metastasis of esophageal cancer, but the numbers of these cells in patients after preoperative radiotherapy were significantly lower than those in patients without radiotherapy. Immunohistochemical staining of cryostat sections with anti-CD1 antibody and L-M2 revealed that poorly differentiated squamous cell carcinoma (SCC) contained significantly more DCs than well differentiated SCC. Analysis of the numbers of Langerhans cells (LCs) and interdigitating cells (IDCs) revealed that well differentiated SCC contained 32.8% LCs and 67.2% IDCs, moderately differentiated SCC contained 37.0% LCs and 63.0% IDCs, and poorly differentiated SCC contained 2.1% LCs and 97.9% IDCs, the overall proportions being 24.2% for LCs and 75.8% for IDCs. Morphometrical analysis of regional primary lymph nodes revealed that the degree of paracortical hyperplasia with cancer metastasis was significantly higher than that without cancer metastasis, and that the degree of sinus hyperplasia with cancer metastasis was significantly lower than that without. Furthermore, lymph nodes with cancer metastasis contained significantly more S-100 protein-positive IDCs than those without.(ABSTRACT TRUNCATED AT 250 WORDS)

Dendritic cells in various human thyroid diseases

The aim of this study is to determine the presence of S-100 protein-positive and CD1-positive dendritic cells (DCs) in tissues with various human thyroid diseases. Infiltrating DCs were frequently observed in papillary carcinoma and Hashimoto's disease, and these DCs were composed primarily of IDCs. The number of DCs was closely correlated with the expression of thyrocytes for S-100 protein and Ia-antigen. These findings suggest that DCs may play an important role in the immunologic defence mechanisms against papillary carcinomas and in the progression and self perpetuation of autoimmunity.

Expression and characterization of cDNAs for cecropin B, an antibacterial protein of the silkworm, Bombyx mori

To analyze the induction mechanism of antibacterial protein gene expression, cDNAs coding for cecropin B have been cloned from the B. mori fat body cDNA library. Nucleotide sequences of two positive clones were determined and their amino acid sequences deduced. They revealed that these clones coded for the same cecropin, which is identical to purified cecropin B. However, the cDNAs contained different nucleotides at the third codon position and 5' or 3' non-coding regions. Results obtained by Northern blot analysis showed that the gene expression of B. mori cecropin B was rapidly induced by Escherichia coli and reached maximum levels 8 h after immunization. The expression of cecropin B gene occurred specifically in tissues, mainly in the fat body and hemocytes.

[In vitro chemosensitivity assay using a double-layer-agar system: human tumor cloning assay and thymidine incorporation assay]

Human tumor cloning assay (HTCA) and thymidine incorporation assay (TIA) were both performed using a double-layer-agar system with continuous exposure of cells to standard anticancer drugs. The rate of evaluable assays was 44% (280 of 638 tumor samples) in HTCA and 48% (216 of 452) in TIA. When the tumor samples were restricted to the gastric and colorectal cancers, it was significantly higher in TIA than HTCA (p < 0.01). HTCA was 95% reliable for predicting in vivo resistance and 52% reliable for in vivo sensitivity, whereas TIA was 88% reliable for in vivo resistance and 44% for in vivo sensitivity. These results seem to suggest that it is unnecessary to select just clonogenic tumor cells among whole tumor cell population in assessing chemosensitivity of human tumors. The current study also indicates that chemotherapy with in vitro sensitive drugs assessed by TIA produced longer survival of the patients with stage III or IV gastric cancer. Most of clinical correlation trials including this study, however, have been performed retrospectively. The prospective study is necessary to determine whether drug selection by in vitro assays is superior to that by an experienced oncologist. In addition, further studies on pharmacokinetics of anticancer drugs are required to solve some other problems inherent to the current chemosensitivity assays.

[Experimental study of tumor response to twice-a-day irradiation at smaller doses than 2 Gy]

Tumor response to twice-a-day irradiation (BID) at smaller doses than 2 Gy on mammary carcinoma of C3H/He mouse (alpha/beta ratio = 18 Gy) was studied with comparison of once-a-day irradiation (QD) in the same overall treatment time. The dose per fraction (dBID) was ranged from 110R to 162R in BID, and the dose per fraction (dQD) was ranged from 200R to 300R in QD fractionation (1R = 0.91 cGy). The number of fraction was 10 or 15 in QD, and 20 or 30 in BID. The interval of fractions was 4 hours in BID. Tumor response was assessed by tumor growth delay. MFD effect ratio, i.e., growth delay time of BID/growth delay time of QD, was significantly smaller than the ratio estimated from FDF formula, (alpha/beta + dBID) x dBID x NBID/(alpha/beta + dQD) x dQD x NQD, with decreasing fraction size. In the case of dBID = 120R and dQD = 200R, estimated ratio was 1.16, but MFD effect ratio was 0.58, regardless of 20% increments of daily dose. To get same or more tumor response, it is necessary to prolong the overall treatment time of twice-a-day irradiation. If the overall treatment time is same, it is estimated that the fraction size of BID equivalent to the fractionation of daily 200R is presumably 135R to this mouse tumor.

Agonist activation modulates cross-bridge states in single vascular smooth muscle cells

To determine cross-bridge properties during agonist-stimulated contractions, steady-state force and relative steady-state stiffness were recorded at rest (pCa 9) and during both full (pCa 4) and partial (pCa 7) Ca2+ activations of isolated single alpha-toxin permeabilized vascular smooth muscle cells. For pCa 4 and pCa 7, agonist (1 microM histamine) activation resulted in significant (P < 0.05) increases in both force and stiffness. The agonist-induced increase of steady-state force was significantly (P < 0.05) greater than that of stiffness; at pCa 4, there was a 48% increase for force vs. 17% for stiffness, and, at pCa 7, there was a 160% increase for force vs. 57% for stiffness. The increase in force and stiffness after agonist prestimulation implies that the number of attached cross bridges has increased. However, after agonist prestimulation, we found that the increase of force was greater (P < 0.05) than that of stiffness, resulting in a greater force at any given level of stiffness. Thus these data indicate that agonist activation, presumably via activation of a G protein, increases the relative force per attached cross bridge, possibly by modulating the kinetics of the actomyosin adenosinetriphosphatase to increase in the relative population of cross bridges in force-producing states [actinomyosin (AM) or AM.ADP].

Quantitative structure-activity relationships of antibacterial agents, 7-heterocyclic amine substituted 1-cyclopropyl-6,8-difluoro-4-oxoquinoline-3-carboxylic acids

Quantitative structure-activity relationships (QSAR) of various 7-(3-substituted-azetidin-1-yl)-1-cyclopropyl-6,8-difluoro-1,4-dih ydro-4- oxoquinoline-3-carboxylic acids, 14-25, were studied to clarify the structural requirements for 3-substituted azetidines to potentiate antibacterial activity. A good parabolic relationship seemed to exist between the relative mean antibacterial activity indices against five representative gram-negative bacteria, GNM, and the calculated hydrophobic parameters, CLOG P, of these molecules. The CLOG P value of the most potent derivative was predicted to be around 2.3. On the other hand, against five representative gram-positive bacteria, the relative mean antibacterial activity indices, GPM, remained high and rather constant regardless of structural variation in the azetidine moiety. In order to confirm these findings, the QSAR analysis was extended with success to the quinolonecarboxylic acids, 26-34, which bear various substituted pyrrolidine, piperazine and piperidine derivatives instead of azetidines. The findings showed that the introduction of any amide substituent group to these heterocyclic amine moieties would lead to marked decrease in GNM, whereas incorporation of some amino substituent groups at a position two or three carbons remote from the N-1 position resulted in great enhancement of GNM. As azetidine quinolones exhibited somewhat low in vivo antibacterial activities, possibly reflecting their lesser bioavailability, we finally selected 3-amino-4-methoxypyrrolidine as one of the most promising C-7 substituent groups based on our QSAR analysis.

Myosin light chain-2 mutation affects flight, wing beat frequency, and indirect flight muscle contraction kinetics in Drosophila

We have used a combination of classical genetic, molecular genetic, histological, biochemical, and biophysical techniques to identify and characterize a null mutation of the myosin light chain-2 (MLC-2) locus of Drosophila melanogaster. Mlc2E38 is a null mutation of the MLC-2 gene resulting from a nonsense mutation at the tenth codon position. Mlc2E38 confers dominant flightless behavior that is associated with reduced wing beat frequency. Mlc2E38 heterozygotes exhibit a 50% reduction of MLC-2 mRNA concentration in adult thoracic musculature, which results in a commensurate reduction of MLC-2 protein in the indirect flight muscles. Indirect flight muscle myofibrils from Mlc2E38 heterozygotes are aberrant, exhibiting myofilaments in disarray at the periphery. Calcium-activated Triton X-100-treated single fiber segments exhibit slower contraction kinetics than wild type. Introduction of a transformed copy of the wild type MLC-2 gene rescues the dominant flightless behavior of Mlc2E38 heterozygotes. Wing beat frequency and single fiber contraction kinetics of a representative rescued line are not significantly different from those of wild type. Together, these results indicate that wild type MLC-2 stoichiometry is required for normal indirect flight muscle assembly and function. Furthermore, these results suggest that the reduced wing beat frequency and possibly the flightless behavior conferred by Mlc2E38 is due in part to slower contraction kinetics of sarcomeric regions devoid or partly deficient in MLC-2.