Residency Application Advising: Medical Student & Faculty Advisor Perceived Barriers & Expectations

INTRODUCTION

Given the rapidly changing landscape of residency applications, many medical students struggle to identify guidance from faculty advisors. Additionally, faculty advisors may find it difficult to maintain up-to-date knowledge on changes such as the new supplemental application. These gaps could potentially lead to inequitable advising. The objective of this study was to identify both students' and faculty's perceived barriers and expectations for residency application advising.

METHODS

Anonymous surveys were administered to both fourth-year medical students and faculty advisors at a single institution within 2 mo of the residency application deadline. Survey questions assessed student and faculty barriers to establishing the advisor-advisee relationships, as well as expectations of the advisor role. Surveys were analyzed using descriptive statistics.

RESULTS

We identified that the majority of students (57%) did not have a faculty advisor within weeks of the application deadline, and an equal amount felt that finding an advisor was either somewhat difficult or extremely difficult. Of all the students, 60% felt their biggest barrier was not knowing how to find an advisor. Though faculty felt equipped to advise students, 75% of faculty in the participating specialties had advising concerns regarding the supplemental application or were unaware of the changes.

CONCLUSIONS

We identified gaps in the residency application advising process from both student and faculty perspectives. Future work involves increasing awareness of the resources and opportunities available to students to improve advising relationships. Standardized training tools and resources for faculty will result in more consistent and reliable faculty advising.

PPARG dysregulation as a potential molecular target in adrenal Cushing's syndrome

Background

We performed a transcriptomic analysis of adrenal signaling pathways in various forms of endogenous Cushing's syndrome (CS) to define areas of dysregulated and druggable targets.

Methodology

Next-generation sequencing was performed on adrenal samples of patients with primary bilateral macronodular adrenal hyperplasia (PBMAH, n=10) and control adrenal samples (n=8). The validation groups included cortisol-producing adenoma (CPA, n=9) and samples from patients undergoing bilateral adrenalectomy for Cushing's disease (BADX-CD, n=8). In vivo findings were further characterized using three adrenocortical cell-lines (NCI-H295R, CU-ACC2, MUC1).

Results

Pathway mapping based on significant expression patterns identified PPARG (peroxisome proliferator-activated receptor gamma) pathway as the top hit. Quantitative PCR (QPCR) confirmed that PPARG (l2fc<-1.5) and related genes - FABP4 (l2fc<-5.5), PLIN1 (l2fc<-4.1) and ADIPOQ (l2fc<-3.3) - were significantly downregulated (p<0.005) in PBMAH. Significant downregulation of PPARG was also found in BADX-CD (l2fc<-1.9, p<0.0001) and CPA (l2fc<-1.4, p<0.0001). In vitro studies demonstrated that the PPARG activator rosiglitazone resulted in decreased cell viability in MUC1 and NCI-H295R (p<0.0001). There was also a significant reduction in the production of aldosterone, cortisol, and cortisone in NCI-H295R and in Dihydrotestosterone (DHT) in MUC1 (p<0.05), respectively.

Outcome

This therapeutic effect was independent of the actions of ACTH, postulating a promising application of PPARG activation in endogenous hypercortisolism.

Histopathology and Genetic Causes of Primary Aldosteronism in Young Adults

CONTEXT

Due to its rare incidence, molecular features of primary aldosteronism (PA) in young adults are largely unknown. Recently developed targeted mutational analysis identified aldosterone-driver somatic mutations in aldosterone-producing lesions, including aldosterone-producing adenomas (APAs), aldosterone-producing nodules (APNs), and aldosterone-producing micronodules, formerly known as aldosterone-producing cell clusters.

OBJECTIVE

To investigate histologic and genetic characteristics of lateralized PA in young adults.

METHODS

Formalin-fixed, paraffin-embedded adrenal tissue sections from 74 young patients with lateralized PA (<35 years old) were used for this study. Immunohistochemistry (IHC) for aldosterone synthase (CYP11B2) was performed to define the histopathologic diagnosis. Somatic mutations in aldosterone-producing lesions were further determined by CYP11B2 IHC-guided DNA sequencing.

RESULTS

Based on the CYP11B2 IHC results, histopathologic classification was made as follows: 48 APAs, 20 APNs, 2 multiple aldosterone-producing nodules (MAPN), 1 double APN, 1 APA with MAPN, and 2 nonfunctioning adenomas (NFAs). Of 45 APAs with successful sequencing, 43 (96%) had somatic mutations, with KCNJ5 mutations being the most common genetic cause of young-onset APA (35/45, 78%). Of 18 APNs with successful sequencing, all of them harbored somatic mutations, with CACNA1D mutations being the most frequent genetic alteration in young-onset APN (8/18, 44%). Multiple CYP11B2-expressing lesions in patients with MAPN showed several aldosterone-driver mutations. No somatic mutations were identified in NFAs.

CONCLUSION

APA is the most common histologic feature of lateralized PA in young adults. Somatic KCNJ5 mutations are common in APAs, whereas CACNA1D mutations are often seen in APNs in this young PA population.

Concomitant Pheochromocytoma and Primary Aldosteronism: A Case Series and Literature Review

Context

The detection and management of concomitant pheochromocytoma (PHEO) and primary aldosteronism (PA) is not well understood.

Objective

To investigate varying presentations and outcomes of cases with coexisting PHEO and PA to provide an approach to its diagnosis and management.

Methods

We conducted a retrospective case series of adult patients with concomitant PHEO and PA at Mayo Clinic from 2000-2020 and an additional review of cases before 2000 and from the medical literature. Clinical, biochemical, radiologic, and histologic parameters were measured.

Results

Fifteen patients (53% men, median age 53 years) were diagnosed with concomitant PHEO and PA. The majority presented with hypertension (13, 87%) and hypokalemia (13, 87%), and 6 (40%) presented with symptoms suggestive of catecholamine excess. All patients who underwent preoperative workup for catecholamine excess (14, 93%) were found to have biochemical levels above the upper limits of normal. Adrenal vein sampling (AVS) was performed in 9 patients (60%), where 5 (56%) were diagnosed with bilateral PA, and 4 (44%) with unilateral PA. Patients underwent either unilateral (12, 80%) or bilateral (3, 20%) adrenalectomy. Biochemical improvement or resolution of catecholamine excess was confirmed in all cases with documented measurements. Recurrence of PHEO was not observed. Six patients (40%) displayed persistent PA postoperatively.

Conclusion

Concomitant PHEO and PA is a rare but likely underreported condition. Hypertension with or without hypokalemia should prompt evaluation for PA, while any indeterminate adrenal mass should be assessed for PHEO. Coexisting disease warrants consideration of AVS to determine the laterality of PA to ensure appropriate management.

Targeted RNA sequencing of adrenal zones using immunohistochemistry-guided capture of formalin-fixed paraffin-embedded tissue

Adequate access to fresh or frozen normal adrenal tissue has been a primary limitation to the enhanced characterization of the adrenal zones via RNA sequencing (RNAseq). Herein, we describe the application of targeted RNAseq to formalin-fixed paraffin-embedded (FFPE) normal adrenal gland specimens. Immunohistochemistry (IHC) was used to visualize and guide the capture of the adrenocortical zones and medulla. Following IHC-based tissue capture and isolation of RNA, high-throughput targeted RNAseq highlighted clear transcriptomic differences and identified differentially expressed genes among the adrenal zones. Our data demonstrate the ability to capture FFPE adrenal zone tissue for targeted transcriptomic analyses. Future comparison of normal adrenal zones will improve our understanding of transcriptomic patterns and help identify potential novel pathways controlling zone-specific steroid production.

Masking by hypokalemia-primary aldosteronism with undetectable aldosterone

Primary aldosteronism is the most common cause of secondary hypertension; however, the dynamic regulation of aldosterone by potassium is less well studied and current diagnostic recommendations are imprecise. We describe a young man who presented with resistant hypertension and severe hypokalemia. The workup initially revealed undetectable aldosterone despite acute potassium repletion. Chronic potassium supplementation eventually uncovered hyperaldosteronism. In situ genetic studies revealed a gain-of-function KCNJ5 mutation within an aldosterone-producing adenoma that was clinically responsive to changes in extracellular potassium. We highlight a unique presentation of Conn's syndrome and discuss the implications for the molecular mechanisms of potassium regulation of aldosterone.

SAT-554 Genetic Profile of Early-Onset Aldosterone-Producing Adenomas

Background: Aldosterone-producing adenoma (APA) is a major subtype of primary aldosteronism (PA) which is the most common cause of endocrine-related hypertension. The Endocrine Society clinical practice guideline suggests that young patients (< 35 years old) with a CT-detected adrenocortical adenoma and typical phenotype of PA may not need adrenal venous sampling prior to adrenalectomy. In recent years, aldosterone-driver somatic mutations have been identified in APA, and prevalence studies suggest potential effects of patient age and sex. However, the rare nature of early-onset PA has prevented a detailed study of the histologic characteristics and aldosterone-driver somatic mutations in adrenal tumors from these patients.

Objective: To determine histologic and somatic mutation profile in early-onset APA.

Methods: Fifty-five formalin-fixed paraffin-embedded (FFPE) adrenals from patients at the age of 35 years old or younger who underwent adrenalectomy at the participating centers were studied (45 women, 9 men, and 1 unknown sex). CYP11B2 immunohistochemistry (IHC)-guided tumor capturing was used to selectively obtain DNA from APA. Mutation status was determined either by Sanger sequencing or targeted next-generation sequencing.

Results: CYP11B2 IHC identified APAs in all adrenal specimens. Solitary APAs were found in 53 adrenals. One adrenal had multiple APAs and one had a dominant CYP11B2-negative tumor and a smaller APA. In total, DNA from 57 APAs were sequenced. Two APAs were excluded from the analysis due to low sample quality. In 52 of the 55 APAs, somatic mutations were identified in one of the aldosterone-driver genes or CTNNB1 gene, encoding β-catenin. The most common genetic alteration was seen in KCNJ5 (37/55, 67%), followed by CACNA1D (7/55, 13%), ATP1A1 (3/55, 5%), CTNNB1 (3/55, 5%), and ATP2B3 (2/55, 4%). No sex difference in the prevalence of KCNJ5 mutation was observed in this age group.

Conclusion: The majority of adrenals from early-onset PA patients had a solitary APA. Regardless of sex, the most common genetic cause of early-onset APA was somatic mutations in KCNJ5.

Effects of activated carbon on reductive dechlorination of PCBs by organohalide respiring bacteria indigenous to sediments

Polychlorinated biphenyls (PCBs) have accumulated in aquatic sediments due to their inherent chemical stability and their presence poses a risk due to their potential toxicity in humans and animals. Granular activated carbon (GAC) has been applied to PCB contaminated sediment sites to reduce the aqueous concentration by sequestration thus reducing the PCB exposure and toxicity to both benthic and aquatic organisms. However, it is not known how the reduction of PCB bioavailability by adsorption to GAC affects bacterial transformation of PCBs by indigenous organohalide respiring bacteria. In this study, the impact of GAC on anaerobic dechlorination by putative organohalide respiring bacteria indigenous to sediment from Baltimore Harbor was examined. It was shown that the average Cl/biphenyl after dehalogenation of Aroclor 1260 was similar between treatments with and without GAC amendment. However, GAC caused a substantial shift in the congener distribution whereby a smaller fraction of highly chlorinated congeners was more extensively dechlorinated to mono- through tri-chlorinated congeners compared to the formation of tri- through penta-chlorinated congeners in unamended sediment. The results combined with comparative sequence analysis of 16S rRNA gene sequences suggest that GAC caused a community shift to putative organohalide respiring phylotypes that coincided with more extensive dechlorination of ortho and unflanked chlorines. This shift in activity by GAC shown here for the first time has the potential to promote greater degradation in situ by promoting accumulation of less chlorinated congeners that are generally more susceptible to complete mineralization by aerobic PCB degrading bacteria.

Behavior analytic studies of creativity: A critical review

Studies that treat creativity as operant behavior were critically reviewed. Of the twenty studies, most met minimal requirements for methodological adequacy; all provided at least some evidence for increased creative responding. Major difficulties involved potential confounds between instructions and contingencies, lack of an independent record of the training interaction, lack of social validation data, and very limited evidence for generalization. Several issues were discussed: problems in the behavioral definition of creativity, objections to the use of contingent reinforcement, and the need for empirical analysis of the creative process.

A randomized trial of high-dose vitamin D2 in relapsing-remitting multiple sclerosis

OBJECTIVE

Higher latitude, lower ultraviolet exposure, and lower serum 25-hydroxyvitamin D (25OHD) correlate with higher multiple sclerosis (MS) prevalence, relapse rate, and mortality. We therefore evaluated the effects of high-dose vitamin D2 (D2) in MS.

METHODS

Adults with clinically active relapsing-remitting MS (RRMS) were randomized to 6 months' double-blind placebo-controlled high-dose vitamin D2, 6,000 IU capsules, dose adjusted empirically aiming for a serum 25OHD 130-175 nM. All received daily low-dose (1,000 IU) D2 to prevent deficiency. Brain MRIs were performed at baseline, 4, 5, and 6 months. Primary endpoints were the cumulative number of new gadolinium-enhancing lesions and change in the total volume of T2 lesions. Secondary endpoints were Expanded Disability Status Scale (EDSS) score and relapses.

RESULTS

Twenty-three people were randomized, of whom 19 were on established interferon or glatiramer acetate (Copaxone) treatment. Median 25OHD rose from 54 to 69 nM (low-dose D2) vs 59 to 120 nM (high-dose D2) (p = 0.002). No significant treatment differences were detected in the primary MRI endpoints. Exit EDSS, after adjustment for entry EDSS, was higher following high-dose D2 than following low-dose D2 (p = 0.05). There were 4 relapses with high-dose D2 vs none with low-dose D2 (p = 0.04).

CONCLUSION

We did not find a therapeutic advantage in RRMS for high-dose D2 over low-dose D2 supplementation.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that high-dose vitamin D2 (targeting 25OHD 130-175 nM), compared to low-dose supplementation (1,000 IU/d), was not effective in reducing MRI lesions in patients with RRMS.

A new HLA-A*31 null allele, A*3114N

A new HLA-A*31 null allele results from addition of an extra C near the beginning of exon 4 after a string of seven Cs.

Concentrations of polychlorinated biphenyl congeners in cultivated oysters (Crassostrea gigas) in western Taiwan

Spatial and temporal variations of polychlorinated biphenyl (PCB) concentrations in cultivated oysters from five aquaculture areas along the western coast of Taiwan were investigated. Poor correlations between total PCB concentrations (ng/g dry weight [dw]) and physiologic parameters of oysters (shell length, width, thickness, and lipid content) were found. Total PCB concentrations ranged from 3.4 to 94 cng/g dw. The highest value was found in oysters from the Lu'ermen aquaculture area, which receives wastewater from a sodium hydroxide and pentachlorophenol factory. Furthermore, principal component analysis confirmed that the PCB congener pattern in this area was distinct from others and that two additional pollution sources might exist in the Tainan and Hsinchu areas. Oysters with PCB concentrations > 1 SD above the geometric mean were found mainly in Tainan (stations TN5 to TN9) with only one increased concentration in the Yunlin (station YL2) and Hsinchu (station HC4) aquaculture areas. Except for four confined stations, TN3 to TN6, where total PCB concentrations were higher (p = 0.028) in the warmer (May and July) than in the colder season (November and March), seasonal variation of total PCB concentrations in oysters was not significant. Geometric mean and geometric mean plus 1 SD of total PCB concentrations in this study are lower than those in South Korea and the United States (Mussel Watch).

HLA class I null alleles and new alleles affect unrelated bone marrow donor searches

Unrecognized HLA null alleles or new alleles may affect the outcome of bone marrow transplants using unrelated donors. Some reports suggest that null alleles occur in the range of 0.003-0.07% (1, 2), which has led some transplant programs to stop performing serologic typing. We describe nine cases involving expression variants or new alleles. Three cases involved expression variants, including two null alleles and A*24020102L. One of the null alleles was a new variant of A*02. Seven cases involved new alleles. In five cases, there where discrepancies between HLA typing by serology and PCR-SSP. These included the three expression variants, one new B40 allele that typed serologically as B41 and one new B*07 allele that typed serologically as B42. Eight of these cases were found in the course of typing bone marrow transplant patients or potential unrelated donors since May of 2001 (total tested, 710 patients, 1914 donors). Thus, the incidence of null alleles was two in 2,624 (0.08%). Sequence-based typing (SBT) was performed on 676 of these samples. The decision to perform SBT was influenced by finding a serologic typing discrepancy in two cases. In one of those cases, SBT would probably have been performed at a later time, prior to final selection of a donor. Thus, the incidence of new alleles was between 4 and 6 of 676 (0.59-0.89%). We conclude that new HLA alleles and null alleles are uncommon but not extremely rare, and they continue to affect a significant number of unrelated donor searches.

Comparing polybrominated diphenyl ether and polychlorinated biphenyl bioaccumulation in a food web in Grand Traverse Bay, Lake Michigan

Levels of polybrominated diphenyl ethers (BDEs) in Great Lakes salmonids and ambient air have been recently reported, but few studies worldwide have examined the accumulation of BDEs within aquatic food webs. Here we report some of the first measurements of six BDE congeners that are common components of the pentaBDE commercial mixture within an entire Lake Michigan food web. BDEs were detected in all samples and the dominant BDE congener was 2,2',4,4'-tetrabromodiphenyl ether (BDE 47). BDE 47 levels were consistently greater than those of the 2,2',4,4',5-pentabromodiphenyl ether (BDE 99), despite similar levels of these two compounds in commercial mixtures, suggesting differences in the bioavailability of the BDE congeners or differences in their ability to be metabolized. Additionally, congener composition was significantly different among deepwater sculpin, bloater chub, and lake trout, indicating differences in exposure or differences in biotransformation capacities. Total BDE concentrations in this food web were positively correlated (r = 0.94) with levels of PCBs previously measured in these samples (Stapleton et al. 2001a). Levels of BDE 47 and PCB 153, compounds with similar physicochemical properties, were compared to examine the relative exposure and bioaccumulation of these two classes of chemicals that have different environmental loading histories. Food web magnification factors calculated for these two congeners were 3.2 and 4.0 for BDE 47 and PCB 153, respectively, indicating a comparable potential for biomagnification in food webs.

cDNA cloning, purification, properties, and function of a beta-1,3-glucan recognition protein from a pyralid moth, Plodia interpunctella

Microorganisms possess distinctive biochemical or molecular patterns on their cell surfaces, such as those formed by the lipopolysaccharides, lipoteichoic acids, and/or peptidoglycans of bacteria and the beta-1,3-glucans of fungi. Pattern recognition proteins that bind to these surface moieties have been implicated in the activation of the innate immune response in insects and other invertebrates. We report the purification and cloning of a cDNA for a 53-kDa beta-1,3-glucan recognition protein (betaGRP) from the Indianmeal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae). BetaGRP cDNA contains an open reading frame that encodes 488 amino acids, of which the first 17 residues comprise the secretion signal peptide. The calculated molecular mass of the 471-residue mature protein is 53,311 Da. The protein consists of a carboxyl-terminal domain that is similar to other recognition proteins from invertebrates, beta-1,3-glucanases from bacteria, and a beta-1,3-glucanase from the sea urchin, Strongylocentrotus purpuratus. The amino-terminus of betaGRP shares sequence similarity with other invertebrate recognition molecules and the beta-1,3-glucanase from S. purpuratus. Affinity purification of a 53-kDa protein and subsequent sequencing of a peptide produced by tryptic cleavage confirmed the presence of the betaGRP in P. interpunctella larval hemolymph. RT-PCR analysis indicates that betaGRP is constitutively expressed in all life-stages, with no detectable induction following exposure of wandering larvae to microbial elicitors. Northern blot analysis indicates that the 1.8-kb betaGRP transcript is transcribed within the fat body. Recombinant betaGRP retains beta-1,3-glucan-binding activity, binds to lipopolysaccharide and lipoteichoic acid in vitro, causes aggregation of microorganisms, and activates the prophenoloxidase cascade in the presence of soluble beta-1,3-glucan. These data support the hypothesis that the 53-kDa betaGRP functions to recognize pathogen surface molecules as nonself and subsequently activates insect innate immune responses.

Trigeminal and polyradiculoneuritis in a dog presenting with masticatory muscle atrophy and Horner's syndrome

A 9-year-old, spayed female, Airedale Terrier was euthanatized and necropsied after a progressive clinical course that included Horner's syndrome of the left eye and unilateral atrophy of the masticatory muscles. Although gross lesions were limited, a polyradiculoneuritis and ganglionitis that was most severe in the trigeminal nerves and ganglia were confirmed histologically. The inflammatory infiltrate consisted predominantly of macrophages and B and T lymphocytes that were phenotypically confirmed by immunostaining. Horner's syndrome was the result of damage to postganglionic sympathetic fibers that were incorporated in segments of the inflamed trigeminal nerve and its ophthalmic branch. Histologically, the character and distribution of the inflammation was similar to previously described syndromes of suspected immune-mediated etiology in humans and animals.

Ammonia exchange between the atmosphere and the surface waters at two locations in the Chesapeake Bay

Excess phytoplankton production, which contributes to hypoxic conditions, is nitrogen limited in the Chesapeake Bay during the summer months. Therefore, understanding the flux of ammonia by direct deposition to the biologically active surface layer is critical to understanding the nutrient dynamics of the bay. This paper presents the results of a 2-yr study measuring gaseous ammonia (NH3) and aerosol ammonium (NH4+) in Baltimore and Solomons, MD, from which direct atmospheric loading of total ammonia (Nt = NH3 + NH4+) to the Chesapeake Bay is estimated. Mean atmospheric concentrations of total ammonia for Baltimore and Solomons were 2.7 +/- 1.7 and 1.0 +/- 0.8 microg of N m(-3), respectively. Monte Carlo estimates of gross dry deposition ranged from <100 to 4900 microg of N m(-2) d(-1). However, based upon water quality parameters, Monte Carlo estimates of gross volatilization of NH3 were calculated to range from <100 to 7700 microg of N m(-2) d(-1). The resulting net air-sea exchange flux varied seasonally from a net deposition into the water during the winter to a net volatilizing into the atmosphere during the summer. A total of 60% of the paired air-water samples had flux estimates that were not significantly different than equilibrium at the 90% confidence interval. The gross deposition, gross volatilization, and net air-sea fluxes were greater and more variable in Baltimore relative to the rural site. Atmospheric ammonia concentrations decrease during the winter at the rural site. However, the net exchange is still into the water due to an exponential decrease in [NH3]eq with temperature. These results indicate that the nitrogen-limited Chesapeake Bay can act as a source of ammonia to the local atmosphere.

Metabolism of PCBs by the deepwater sculpin (Myoxocephalus thompsoni)

Methylsulfonyl-PCBs (MeSO2-PCBs) are hydrophobic organic contaminants that bioaccumulate in the environment similar to their parent molecules, PCBs. Previously, MeSO2-PCBs have primarily been identified in tissues of birds, humans, and other mammals. However, evidence now supports formation of these metabolites in deepwater sculpin, Myoxocephalus thompsoni, a benthic forage fish predominant in the Great Lakes. The ability of deepwater sculpin to form MeSO2-PCBs is unprecedented for a freshwater fish species and presents a novel biochemical pathway for organochlorine metabolism. Additionally, this appears to be a unique PCB metabolic pathway resulting in a reduction of as much as 10% in the sculpin PCB burden, which is further transformed into another class of organic contaminants in the Great Lakes ecosystem.

Recent declines in PAH, PCB, and toxaphene levels in the northern Great Lakes as determined from high resolution sediment cores

Sediment cores were collected from two sites in Grand Traverse Bay, Lake Michigan in May 1998, dated using 210Pb geochronology, and analyzed for polychlorinated biphenyl (PCB) congeners, polycyclic aromatic hydrocarbons (PAHs), and toxaphene. The extraordinarily high sediment focusing and accumulation rates in these cores relative to other Great Lakes sediments allowed quantification of high-resolution temporal trends in the burial of hydrophobic organic contaminants. The focus-corrected accumulation rate of total PCBs (sum of 105 congeners) in 1998 was 0.50 ng/cm2-year at both sites. Toxaphene and total PAH (t-PAH; sum of 33 compounds) surficial accumulations varied at each site and ranged from 0.08 to 0.41 ng/cm2-year for toxaphene and 25 to 52 ng/cm2-yr for t-PAHs at the two sites. The maximum t-PAH accumulation rate was in sediment dated from 1942, and PAH accumulation decreased from 1942 to 1980 with a first-order rate of decline 0.017 yr(-1). Both toxaphene and t-PCB accumulations peaked in sediment deposited in 1972, afterwhich their accumulations decreased with nearly identical rates of decline (0.027 yr(-1) and 0.028 yr(-1), respectively).

Accumulation of atmospheric and sedimentary PCBs and toxaphene in a Lake Michigan food web

Seston, sediment, settling organic matter, and food web members were collected from Grand Traverse Bay, Lake Michigan, between April 1997 and September 1998 to examine PCB and toxaphene biomagnification. Stable isotopes of nitrogen and carbon were analyzed in samples and used to establish trophic structure of the food web and to determine the importance of atmospheric versus sedimentary sources in delivering PCBs to the food web. Nitrogen isotopes were confounded by multiple variables in this system, particularly seasonal variation, and did not display a simple pattern of enrichment among trophic levels. However, delta13C displayed little seasonal variation and was positively correlated with PCB concentrations among food web members (r2 = 0.69). Plots of delta13C vs PCBs separate food web members into three distinct groupings comprised of invertebrates, primary forage fish, and predatory fish. Stable isotope values of the primary organic sources indicate that the atmosphere, and not the sediment, is the most likely source of PCBs to the food web of Lake Michigan. Additionally, we suggest that seston may be important in delivering PCBs to pelagic food web members and species that receive a majority of their nutrition through pelagic sources. In contrast, settling particles are implicated in delivering PCBs to benthic organisms and Mysis relicta.

Heat shock protein 90 mediates the balance of nitric oxide and superoxide anion from endothelial nitric-oxide synthase

The balance of nitric oxide (.NO) and superoxide anion (O(2)) plays an important role in vascular biology. The association of heat shock protein 90 (Hsp90) with endothelial nitric-oxide synthase (eNOS) is a critical step in the mechanisms by which eNOS generates.NO. As eNOS is capable of generating both.NO and O(2), we hypothesized that Hsp90 might also mediate eNOS-dependent O(2) production. To test this hypothesis, bovine coronary endothelial cells (BCEC) were pretreated with geldanamycin (GA, 10 microg/ml; 17.8 microm) and then stimulated with the calcium ionophore, (5 microm). GA significantly decreased -stimulated eNOS-dependent nitrite production (p < 0.001, n = 4) and significantly increased -stimulated eNOS-dependent O(2) production (p < 0.001, n = 8). increased phospho-eNOS(Ser-1179) levels by >1.6-fold over vehicle (V)-treated levels. Pretreatment with GA by itself or with increased phospho-eNOS levels. In unstimulated V-treated BCEC cultures low amounts of Hsp90 were found to associate with eNOS. Pretreatment with GA and/or increased the association of Hsp90 with eNOS. These data show that Hsp90 is essential for eNOS-dependent.NO production and that inhibition of ATP-dependent conformational changes in Hsp90 uncouples eNOS activity and increases eNOS-dependent O(2) production.

Sarcolemmal and mitochondrial K(atp)channels mediate cardioprotection in chronically hypoxic hearts

X. Kong, J. S. Tweddell, G. J. Gross and J. E. Baker. Sarcolemmal and Mitochondrial K(ATP)Channels Mediate Cardioprotection in Chronically Hypoxic Hearts. Journal of Molecular and Cellular Cardiology (2001) 33, 1041-1045. Hypoxia from birth increases the resistance of the isolated neonatal heart to ischemia. We determined if increased resistance to ischemia was due to activation of sarcolemmal or mitochondrial K(ATP)channels. Rabbits (n=8/group) were raised from birth in a normoxic (F(I)O(2)=0.21) or hypoxic (F(I)O(2)=0.12) environment for 8-10 days and the heart perfused with Krebs-Henseleit bicarbonate buffer. A mitochondrial-selective K(ATP)channel blocker 5-hydroxydecanoate (5-HD) (300 micromol/l) or a sarcolemmal-selective K(ATP)channel blocker HMR 1098 (30 micromol/l) were added alone or in combination for 20 min prior to a global ischemic period of 30 min, followed by 35 min reperfusion. Recovery of ventricular developed pressure was higher in chronically hypoxic than normoxic hearts. 5-HD and HMR 1098 partially reduced the cardioprotective effect of chronic hypoxia, but had no effect in normoxic hearts. The combination of 5-HD and HMR 1098 abolished the cardioprotective effect of chronic hypoxia. We conclude that both sarcolemmal and mitochondrial K(ATP)channels contribute to cardioprotection in the chronically hypoxic heart.

Protein tyrosine phosphatase CD148-mediated inhibition of T-cell receptor signal transduction is associated with reduced LAT and phospholipase Cgamma1 phosphorylation

In this study, we investigate the role of the receptor-like protein tyrosine phosphatase CD148 in T-cell activation. Overexpression of CD148 in the Jurkat T-cell line inhibited activation of the transcription factor nuclear factor of activated T cells following T-cell receptor (TCR) stimulation but not following stimulation through a heterologously expressed G protein-coupled receptor, the human muscarinic receptor subtype 1. Using a tetracycline-inducible expression system, we show that the TCR-mediated activation of both the Ras and calcium pathways was inhibited by expression of CD148 at levels that approximate those found in activated primary T cells. These effects were dependent on the phosphatase activity of CD148. Analysis of TCR-induced protein tyrosine phosphorylation demonstrated that most phosphoproteins were unaffected by CD148 expression. However, phospholipase Cgamma1 (PLCgamma1) and LAT were strikingly hypophosphorylated in CD148-expressing cells following TCR stimulation, whereas the phosphorylation levels of Slp-76 and Itk were modestly reduced. Based on these results, we propose that CD148 negatively regulates TCR signaling by interfering with the phosphorylation and function of PLCgamma1 and LAT.

Nitric oxide activates the sarcolemmal K(ATP) channel in normoxic and chronically hypoxic hearts by a cyclic GMP-dependent mechanism

Chronic myocardial hypoxia results in elevated nitric oxide (NO) production and increased current through the sarcolemmal K(ATP) channel. We hypothesized these two processes are related and determined whether NO alters the electrophysiology of Purkinje fibers obtained from rabbits (n=12/group) raised in a normoxic (F(I)O2=0.21) or hypoxic (F(I)O2=0.12) environment from birth to 9 days of age. Action potential duration (APD)(90) was shorter (112+/-3 ms v 126+/-3 ms) and maximum diastolic potential (MDP) was more negative (-84+/-2 mV v-80+/-1 mV) in hypoxic hearts compared with normoxic controls. In normoxic hearts the NO donors, S-nitrosoglutathione (GSNO) 50 microM and spermine NONOate (50 microM) shortened APD(90) and increased MDP to levels present in chronically hypoxic hearts. This effect was completely abolished by the K(ATP) channel blocker glibenclamide (3 microM) and by a nitric oxide trap, Carboxy-PTIO (100 microM). The NO carrier glutathione (50 microM) and decomposed spermine NONOate had no effect on APD(90) or MDP. GSNO had no effect in hypoxic hearts; however, when GSNO was combined with glibenclamide APD(90) increased, and MDP decreased to normoxic values. 8-Bromo cGMP (100 microM) shortened APD(90) and increased MDP to levels present in chronically hypoxic hearts. This effect was abolished by glibenclamide. A soluble guanylyl cyclase inhibitor, ODQ (10 microM), had no effect on action potentials in normoxic hearts but in hypoxic hearts resulted in an increase in APD(90) to levels present in normoxic hearts and a decrease in MDP. The effect of ODQ could not be reversed by GSNO. We conclude that NO activates the sarcolemmal K(ATP) channel in normoxic and chronically hypoxic hearts by a cyclic GMP-dependent mechanism.

The light chain binding domain of expressed smooth muscle heavy meromyosin acts as a mechanical lever

Structural data led to the proposal that the molecular motor myosin moves actin by a swinging of the light chain binding domain, or "neck." To test the hypothesis that the neck functions as a mechanical lever, smooth muscle heavy meromyosin (HMM) mutants were expressed with shorter or longer necks by either deleting or adding light chain binding sites. The mutant HMMs were characterized kinetically and mechanically, with emphasis on measurements of unitary displacements and forces in the laser trap assay. Two shorter necked constructs had smaller unitary step sizes and moved actin more slowly than WT HMM in the motility assay. A longer necked construct that contained an additional essential light chain binding site exhibited a 1.4-fold increase in the unitary step size compared with its control. Kinetic changes were also observed with several of the constructs. The mutant lacking a neck produced force at a somewhat reduced level, while the force exerted by the giraffe construct was higher than control. The single molecule displacement and force data support the hypothesis that the neck functions as a rigid lever, with the fulcrum for movement and force located at a point within the motor domain.

Increased mitochondrial K(ATP) channel activity during chronic myocardial hypoxia: is cardioprotection mediated by improved bioenergetics?

Increased resistance to myocardial ischemia in chronically hypoxic immature rabbit hearts is associated with activation of ATP-sensitive K(+) (K(ATP)) channels. We determined whether chronic hypoxia from birth alters the function of the mitochondrial K(ATP) channel. The K(ATP) channel opener bimakalim (1 micromol/L) increased postischemic recovery of left ventricular developed pressure in isolated normoxic (FIO(2)=0.21) hearts to values (42+/-4% to 67+/-5% ) not different from those of hypoxic controls but did not alter postischemic recovery of developed pressure in isolated chronically hypoxic (FIO(2)=0.12) hearts (69+/-5% to 72+/-5%). Conversely, the K(ATP) channel blockers glibenclamide (1 micromol/L) and 5-hydroxydecanoate (5-HD, 300 micromol/L) attenuated the cardioprotective effect of hypoxia but had no effect on postischemic recovery of function in normoxic hearts. ATP synthesis rates in hypoxic heart mitochondria (3.92+/-0.23 micromol ATP. min(-1). mg mitochondrial protein(-1)) were significantly greater than rates in normoxic hearts (2.95+/-0.08 micromol ATP. min(-1). mg mitochondrial protein(-1)). Bimakalim (1 micromol/L) decreased the rate of ATP synthesis in normoxic heart mitochondria consistent with mitochondrial K(ATP) channel activation and mitochondrial depolarization. The effect of bimakalim on ATP synthesis was antagonized by the K(ATP) channel blockers glibenclamide (1 micromol/L) and 5-HD (300 micromol/L) in normoxic heart mitochondria, whereas glibenclamide and 5-HD alone had no effect. In hypoxic heart mitochondria, the rate of ATP synthesis was not affected by bimakalim but was attenuated by glibenclamide and 5-HD. We conclude that mitochondrial K(ATP) channels are activated in chronically hypoxic rabbit hearts and implicate activation of this channel in the improved mitochondrial bioenergetics and cardioprotection observed.

Trypsinogen-like cDNAs and quantitative analysis of mRNA levels from the Indianmeal moth, Plodia interpunctella

Two cDNA fragments encoding full-length trypsinogen-like proteins were cloned from larvae of two strains (RC688s and HD198r) of the Indianmeal moth, Plodia interpunctella (Hübner), which differed in their sensitivity to Bacillus thuringiensis protoxins. One cDNA fragment contained 874 nucleotides, including a 780-nucleotide open reading frame that encoded a trypsinogen-like protein (PiT2b). Another cDNA fragment amplified from both P. interpunctella strains contained 864 nucleotides including a 780 bp open reading frame encoding a second trypsinogen-like protein (PiT2c). The cDNA sequence of PiT2b shared 89% sequence identity with PiT2a, a trypsinogen-like protein cloned previously from this species. The cDNA sequences of PiT2a and PiT2c shared 83% identity. The cDNA sequence identity between PiT2b and PiT2c was 80%. The cDNA for PiT2b from strain RC688s was different at six nucleotide positions from that of PiT2b from strain HD198r. Five nucleotide replacements occurred in the open reading frame leading to amino acid changes at all five positions. There were five nucleotide differences in the cDNAs for PiT2c trypsinogen-like proteins from the two strains. Two nucleotide substitutions in the open reading frame resulted in replacements of two amino acid residues in the deduced protein sequences. Amino acid sequences for PiT2a and PiT2b shared 84% identity, but only 50% identity was observed between PiT2c and the other two trypsinogen-like proteins. The deduced amino acid sequences for PiT2b and PiT2c included both signal and zymogen activation peptides and amino acid sequence motifs which are conserved in seven homologous trypsinogen-like proteins from other insects. Typical features of the putative trypsinogen-like proteins from P. interpunctella included the serine proteinase active site triad (His(81), Asp(133), and Ser(233)), three pairs of cysteine residues for disulfide bridges, and three residues, Asp(227), Gly(250), and Gly(260), that help to confer trypsin-like specificity to the enzymes. Quantitative RT-PCR analyses showed that, in fourth instar larvae, RC688s had 1.6-fold higher PiT2a trypsinogen-like mRNA than did HD198r. Expression of PiT2b mRNA was 3.4-fold higher in HD198r than in RC688s. Expression of PiT2c mRNA was 2.8-fold higher in RC688s than in HD198r. Mean accumulation levels of mRNAs for all three trypsinogen-like proteins were slightly higher in RC688s than in HD198r based on total RNA, and 1.3-fold higher in RC688s than in HD198r based on wet weight of larval body tissues.

Chronic myocardial hypoxia increases nitric oxide synthase and decreases caveolin-3

Nitric oxide synthase (NOS) is believed to play an important role in protecting the myocardium against ischemia. Chronic hypoxia from birth increases NOS activity in the myocardium resulting in enhanced nitric oxide production and increased resistance to ischemia. We examined the effects of chronic hypoxia on NOS gene and protein expression and on NOS protein association with caveolin-3. Rabbits were raised from birth in a normoxic (F(I)O(2) = 0.21) or a hypoxic (F(I)O(2) = 0.12) environment for 9 d, and then the hearts were isolated. Ribonuclease protection assays revealed that chronic hypoxia did not alter NOS transcript levels for NOS1, NOS2, or NOS3. The most abundant transcript was NOS3. Western analysis revealed NOS3 was the only isoform detected. Immunoblots of NOS3 immunoprecipitates showed that chronic hypoxia increases NOS3 protein by 2.0 +/- 0.4-fold and decreases the amount of caveolin-3 that can be coprecipitated with NOS3 by 5.5 +/- 0.9-fold. Immunoblots of normoxic and hypoxic hearts showed that chronic hypoxia decreases the amount of caveolin-3 in heart homogenates by 2. 2 +/- 0.5-fold. These data suggest that a decrease in caveolin-3 plays a role in the mechanisms by which chronic hypoxia increases NOS3 activity in the myocardium.

Host hemolymph proteins and protein digestion in larval Habrobracon hebetor (Hymenoptera: braconidae)

Host plasma proteins and protein digestion in larval parasitoids were studied during trophic interactions of the ectoparasitoid Habrobracon hebetor Say (Hymenoptera: Braconidae), with a host, larvae of the Indianmeal moth, Plodia interpunctella Hübner (Lepidoptera: Pyralidae). We could detect no apparent differences in host hemolymph protein patterns up to 72 h after paralysation and/or parasitization by H. hebetor. A 190 kDa putative apolipophorin I present in host hemolymph could not be detected in the midguts of feeding H. hebetor larvae indicating that it is rapidly digested. The major 60 kDa storage proteins (putative hexamerins) in host hemolymph were detected in the parasitoid midgut and were completely digested 24 h after cessation of feeding and the beginning of cocoon formation. Host hemolymph had a pH of about 6.4. The pH optima of the midgut proteinases in the larval parasitoid were in the alkaline region, but midgut fluid in feeding parasitoid larvae was about pH 6. 8. Based on enzyme activity against selected artificial proteinase substrates including azocasein, N-alpha-benzoyl-L-Arg p-nitroanilide (BApNA), succinyl-Ala-Ala-Pro-Phe p-nitroanilide (SAAPFpNA), succinyl-Ala-Ala-Pro-Leu p-nitroanilide (SAAPLpNA), and inhibition by selected proteinase inhibitors, serine proteinases appear to be the predominant class of enzymes involved in protein digestion in the midguts of H. hebetor. There is also an active aminopeptidase (LpNA) associated with the microsomal fraction of midgut preparations. There was no evidence for preoral digestion or ingestion of proteinases from host hemolymph by the parasitoid larva. There was a very active BApNAase in the soluble fraction of midgut extracts. This activity increased on a per midgut basis up to 24 h after the beginning of cocoon formation but decreased rapidly by 48 h. Two major (P1 and P3) and several minor proteinases were detected in midgut extracts of H. hebetor analysed with gelatin zymograms. The apparent molecular mass of P1 varied from 95 to 49 kDa depending on protein loading. P3 had an apparent molecular mass of 39 kDa that was independent of protein loading. In summary, electrophoretic evidence indicates that host hemolymph protein patterns do not change significantly for at least 72 h after paralysation by H. hebetor. The role, if any, of envenomization in preventing breakdown of hemolymph proteins during this time remains to be determined. Because the predominant host hemolymph proteins, a putative apolipophorin I and the putative hexamerins, are readily digested by the serine proteinases present in the midguts of this parasitoid larva, these or similar proteins would provide an easily digested source of dietary amino acids that could be used for development of artificial diets for this beneficial insect.

Thermodynamics and kinetics of a molecular motor ensemble

If, contrary to conventional models of muscle, it is assumed that molecular forces equilibrate among rather than within molecular motors, an equation of state and an expression for energy output can be obtained for a near-equilibrium, coworking ensemble of molecular motors. These equations predict clear, testable relationships between motor structure, motor biochemistry, and ensemble motor function, and we discuss these relationships in the context of various experimental studies. In this model, net work by molecular motors is performed with the relaxation of a near-equilibrium intermediate step in a motor-catalyzed reaction. The free energy available for work is localized to this step, and the rate at which this free energy is transferred to work is accelerated by the free energy of a motor-catalyzed reaction. This thermodynamic model implicitly deals with a motile cell system as a dynamic network (not a rigid lattice) of molecular motors within which the mechanochemistry of one motor influences and is influenced by the mechanochemistry of other motors in the ensemble.

Increased CD44 expression in human bronchial epithelial repair after damage or plating at low cell densities

We have investigated the effect of mechanical damage, cell density, and cell-derived soluble mediators on CD44 expression in a model of bronchial epithelial repair. CD44 (all isoforms) and variant-containing isoforms (CD44v3, CD44v6, and CD44v9) were identified with flow cytometry and immunocytochemistry with image analysis. After mechanical damage, CD44 expression increased up to 500 microm from the wound edge and for up to 48 h in two human bronchial epithelium-derived cell lines, 16HBE14o- and NCI-H292. CD44 expression was unchanged by interferon-gamma and increased by <50% by tumor necrosis factor-alpha. To exclude other soluble factors, a Vaseline spacer was used to temporarily divide petri dishes, with cells at high density on one side and those at low density on the other. After the spacer was removed, the cells at low cell density growing in the shared medium expressed up to fourfold higher CD44, although cell proliferation was unchanged. Thus increased CD44 expression at low cell density was not mediated by soluble factors and may reflect functional involvement in cell motility, dedifferentiation, or altered cell-substrate adhesion in epithelial repair.

A thermodynamic muscle model and a chemical basis for A.V. Hill's muscle equation

Direct measurements of a relationship between force and actin-myosin biochemistry in muscle suggest that molecular forces in active muscle rapidly equilibrate among. not within, individual myosin crossbridges [Baker et al. (1999) Biophys J 77: 2657 2664]. This observation suggests a thermodynamic model of muscle contraction in which muscle, not an individual myosin crossbridge, is treated as a near-equilibrium system. The general approach can be applied to any ensemble of molecular motors that undergo a physicochemical step against a constant external potential. In this paper we apply the model to a simple two-state crossbridge scheme like that proposed by A.F. Huxley (1957) [Prog Biophys 7: 255 317], and we immediately obtain A.V. Hill's muscle equation. We show that this equation accurately describes steady-state muscle mechanics, biochemistry and energetics. This thermodynamic model provides a novel description of force-dependent actin-myosin kinetics in muscle and provides precise chemical expressions for myosin cooperativity, myosinduty ratios, the number of working strokes per ATP hydrolyzed, muscle efficiency. and energy transfer.

Molecular cloning and characterization of a midgut chymotrypsin-like enzyme from the lesser grain borer, Rhyzopertha dominica

A cDNA encoding a chymotrypsinogen-like protein in midguts of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) was cloned and sequenced. The 901 bp cDNA contains an 816-nucleotide open reading frame encoding 272-amino acids. The predicted molecular mass and pI of the mature enzyme are 23.7 kDa and 4.64, respectively. The encoded protein includes amino acid sequence motifs that are conserved with 5 homologous chymotrypsinogen proteins from other insects. Features of the putative chymotrypsin-like protein from R. dominica include the serine proteinase active site (His(90), Asp(133), Ser(226)), conserved cysteine residues for disulfide bridges, the residues (Gly(220), Gly(243), Asp(252)) that determine chymotrypsin specificity, and both zymogen activation and signal peptides. A TPCK-sensitive caseinolytic protein (P6) with an estimated molecular mass of 24 kDa is present in midgut extracts of R. dominica and can be resolved by electrophoresis on 4-16% polyacrylamide gels. The molecular mass of this caseinolytic enzyme is similar to that of the chymotrypsin deduced from cDNA. Midgut extracts of R. dominica readily hydrolyzed azocasein and N-succinyl-alanine-alanine-proline-phenylalanine-p- nitroanilide (SAAPFpNA), a chymotrypsin-specific substrate. Properties of the enzymes responsible for these activities were partially characterized with respect to distribution in the gut, optimum pH, and sensitivity toward selected proteinase inhibitors. Optimal activity against both azocasein and SAAPFpNA occurs in a broad pH range from about 7 to 10. Both azocasein and SAAPFpNA activities, located primarily in the anterior midgut region, are inhibited by aprotinin, phenylmethyl sulphonylfluoride (PMSF), and soybean trypsin inhibitor (STI). TPCK (N-alpha-tosyl-L-phenylalanine chloromethyl ketone) and chymostatin inhibited more than 60% of SAAPFpNA but only about 10-20% of azocasein activity. These results provide additional evidence for the presence of serine proteinases, including chymotrypsin, in midguts of R. dominica. Arch. Insect Biochem. Physiol. 43:173-184, 2000.Published 2000 Wiley-Liss, Inc.

Resistance to myocardial ischemia in five rat strains: is there a genetic component of cardioprotection?

There is a need to develop new and more consistent animal models of cardioprotection. Traditionally, outbred dogs, rabbits, and rats have been studied. We determined resistance to ischemia in isolated hearts from inbred strains of rats. Hearts from inbred rats: SS/Mcw (Dahl S, Dahl salt-sensitive), DA/Hsd (Dark Agouti), LEW/Hsd (Lewis), and BN/SsN/Mcw (Brown Norway); and from an outbred rat: Hsd:WIST (Wistar) were subjected to 27 min of global, no-flow ischemia, followed by 3 h of reperfusion. Infarct size in the Brown Norway rat was 2.5 times less than that observed in the Dahl S rat, with the Dark Agouti, Lewis, and Wistar rats intermediate in response. Hearts from Brown Norway rats were also most resistant to ischemia in terms of postischemic enzyme leakage and contractile and vascular function compared with other strains. The average polymorphism rate between strains revealed that such strains were genetically diverse. This study demonstrates strain differences in resistance to myocardial ischemia, suggesting these rats could be used to study a genetic and/or environmental basis for these differences and to provide new animal models for the physiological study of cardioprotection.

Alterations in esterases are associated with malathion resistance in Habrobracon hebetor (Hymenoptera: Braconidae)

Biochemical mechanisms of malathion resistance were investigated in a malathion-resistant strain of the parasitoid Habrobracon hebetor Say collected from a farm storage in Kansas. General esterase activities were significantly lower in the resistant strain compared with those in a susceptible strain. However, no significant differences were found in activities of malathion specific carboxylesterase (MCE), glutathione S-transferase and cytochrome P450 dependent O-demethylase activities, cytochrome P450 contents, and sensitivity of acetylcholinesterase to inhibition by malaoxon between the 2 strains. Because MCE was not elevated in the resistant strain, the weak malathion resistance in H. hebetor may result from a different mechanism compared with that hypothesized for some insect species in which reduced general esterase activity is accompanied by an elevated MCE. Decreased esterase activity in the resistant strain suggested that null alleles of some esterases were associated with the resistance. Indeed, E1 and E2, major esterases in the susceptible strain, were not present in the resistant strain on polyacrylamide gels that were stained for esterase activity using the model substrate 1-naphthyl acetate. In contrast, the activity of esterase E3 on the gels was much higher in the resistant strain as compared with that of the susceptible strain. These findings indicate that malathion resistance in H. hebetor is associated with both an increased activity of the esterase E3 and null alleles of the esterases E1 and E2.

Characterization of midgut trypsin-like enzymes and three trypsinogen cDNAs from the lesser grain borer, Rhyzopertha dominica (Coleoptera: Bostrichidae)

Protein digestion in the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), results from the action of a complex of serine proteinases present in the midgut. In this study we partially characterized trypsin-like enzyme activity against N-alpha-benzoyl-L-arginine p-nitroanilide (BApNA) in midgut preparations and cloned and sequenced three cDNAs for trypsinogen-like proteins. BApNAase activity in R. dominica midgut was significantly reduced by serine proteinase inhibitors and specific inhibitors of trypsin, whereas BApNAase activity was not sensitive to specific inhibitors of chymotrypsin or aspartic proteinases. However, trans-epoxysuccinyl-L-leucylamido-(4-guanidino) butane (E-64) inhibited BApNAase activity by about 30%. BApNAase was most active in a broad pH range from about pH 7 to 9.5. The gut of R. dominica is a tubular tract approximately 2.5 mm in length. BApNAase activity was primarily located in the midgut region with about 1.5-fold more BApNAase activity in the anterior region compared to that in the posterior region. Proteinases with apparent molecular masses of 23-24 kDa that were visualized on casein zymograms following electrophoresis were inhibited by TLCK. Three cDNAs for trypsinogen-like proteins were cloned and sequenced from mRNA of R. dominica midgut. The full cDNA sequences consisted of open reading frames encoding 249, 293, and 255 amino acid residues for RdoT1, RdoT2, and RdoT3, respectively. cDNAs RdoT1, RdoT2, and RdoT3 shared 77-81% sequence identity. The three encoded trypsinogens shared 54-62% identity in their amino acid sequences and had 16-18 residues of signal peptides and 12-15 residues of activation peptides. The three predicted mature trypsin-like enzymes had molecular masses of 23.1, 28, and 23.8 kDa for RdoT1, RdoT2, and RdoT3, respectively. Typical features of these trypsin-like enzymes included the conserved N-terminal residues IVGG62-65, the catalytic amino acid triad of serine proteinase active sites (His109, Asp156, Ser257), three pairs of conserved cysteine residues for disulfide bridges, and the three residues (Asp251, Gly274, Gly284) that determine specificity in trypsin-like enzymes. In addition, RdoT2 has both a PEST-like sequence at the C-terminus and a free Cys158 near the active site, suggesting instability of this enzyme and/or sensitivity to thiol reagents. The sequences have been deposited in GenBank database (accession numbers AF130840 for RdoT1, AF130841 for RdoT2, and AF130842 for RdoT3).

Mechanochemical coupling in spin-labeled, active, isometric muscle

Observed effects of inorganic phosphate (P(i)) on active isometric muscle may provide the answer to one of the fundamental questions in muscle biophysics: how are the free energies of the chemical species in the myosin-catalyzed ATP hydrolysis (ATPase) reaction coupled to muscle force? Pate and Cooke (1989. Pflugers Arch. 414:73-81) showed that active, isometric muscle force varies logarithmically with [P(i)]. Here, by simultaneously measuring electron paramagnetic resonance and the force of spin-labeled muscle fibers, we show that, in active, isometric muscle, the fraction of myosin heads in any given biochemical state is independent of both [P(i)] and force. These direct observations of mechanochemical coupling in muscle are immediately described by a muscle equation of state containing muscle force as a state variable. These results challenge the conventional assumption mechanochemical coupling is localized to individual myosin heads in muscle.

Myosin light-chain domain rotates upon muscle activation but not ATP hydrolysis

We have studied the correlation between myosin structure, myosin biochemistry, and muscle force. Two distinct orientations of the myosin light-chain domain were previously resolved using electron paramagnetic resonance (EPR) spectroscopy of spin-labeled regulatory light chains in scallop muscle fibers. In the present study, we measured isometric force during EPR spectral acquisition, in order to define how these two light-chain domain orientations are coupled to force and the myosin ATPase cycle. When muscle fibers are partially activated with increasing amounts of calcium, the distribution between the two light-chain domain orientations shifts toward the one associated with strong actin binding. This shift in distribution is linearly related to the increase in force, suggesting that rotation of the light-chain domain is coupled to strong actin binding. However, when nucleotide analogues are used to trap myosin in the pre- and posthydrolysis states of its ATPase cycle in relaxed muscle, there is no change in the distribution between light-chain domain orientations, showing that the rotation of the light-chain domain is not directly coupled to the ATP hydrolysis step. Instead, it is likely that in relaxed muscle the myosin thick filament stabilizes two light-chain domain orientations that are independent of the nucleotide analogue bound at the active site. We conclude that a large and distinct rotation of the light-chain domain of myosin is responsible for force generation and is coupled to strong actin binding but is not coupled to a specific step in the myosin ATPase reaction.

Adaptation to chronic hypoxia confers tolerance to subsequent myocardial ischemia by increased nitric oxide production

Chronic exposure to hypoxia from birth increased the tolerance of the rabbit heart to subsequent ischemia compared with age-matched normoxic controls. The nitric oxide donor GSNO increased recovery of post-ischemic function in normoxic hearts to values not different from hypoxic controls, but had no effect on hypoxic hearts. The nitric oxide synthase inhibitors L-NAME and L-NMA abolished the cardioprotective effect of hypoxia. Message and catalytic activity for constitutive nitric oxide synthase as well as nitrite, nitrate, and cGMP levels were elevated in hypoxic hearts. Inducible nitric oxide synthase was not detected in normoxic or chronically hypoxic hearts. Increased tolerance to ischemia in rabbit hearts adapted to chronic hypoxia is associated with increased expression of constitutive nitric oxide synthase.

Differential mRNA expression levels and gene sequences of a putative carboxylesterase-like enzyme from two strains of the parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae)

Carboxylesterase-like enzyme cDNAs have been cloned and sequenced from malathion-resistant and susceptible strains of the parasitoid Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae). The cDNAs consist of 1963 nucleotides including a 35 bp untranslated 5'-end, a 1596 bp open reading frame, and a 332 bp untranslated 3'-end. The open reading frame encodes 532 amino acid residues. The predicted protein sequence from these cDNAs includes 2 potential N-glycosylation sites, a carboxylesterase type-B serine active site FGGDSENVTIFGESAG, and conserved residues Ser187, Glu317, and His432 to function as the catalytic triad. The predicted carboxylesterase-like enzyme sequence is most similar to that of the carboxylesterase from the peach-potato aphid, Myzus persicae with 45% sequence identity. Alignment of the parasitoid carboxylesterase-like enzyme cDNAs revealed that there are two nucleotide differences in the open reading frame between the parasitoid strains, including a silent mutation and a point mutation that presumably causes a gene product difference. A nucleotide thymine at position 658 in the susceptible strain cDNA is replaced by a guanine in the resistant strain cDNA. This substitution leads to an amino acid change from tryptophan (Trp220) in the susceptible strain to glycine (Gly220) in the resistant strain. This substitution is genetically linked to resistance but it is not known how or if this amino acid substitution affects detoxification of malathion. Northern blot analyses demonstrated that expression level of the carboxylesterase-like enzyme mRNA in adult A. calandrae is approximately 30-fold higher in the resistant strain relative to that in the susceptible strain. Southern analysis indicated that Pst I or Eco RI restriction sites are different in the two strains. Both a modified gene structure and an increase in expression of carboxylesterase may be responsible for the high level of resistance found in this beneficial wasp.

Preconditioning in immature rabbit hearts: role of KATP channels

BACKGROUND

The protective effects of ischemic preconditioning have been shown to occur in adult hearts of all species studied. We determined whether immature hearts normoxic or chronically hypoxic from birth could be preconditioned, the time window or memory of the cardioprotective effect, and the involvement of the KATP channel.

METHODS AND RESULTS

Isolated immature rabbit hearts (7 to 10 days old) were subjected to 0, 1, or 3 cycles of preconditioning consisting of 5 minutes of global ischemia plus 10 minutes of reperfusion. This was followed by 30 minutes of global ischemia and 35 minutes of reperfusion. Normoxic hearts (FIO2=0.21) subjected to 1 cycle of preconditioning recovered 70+/-7% of left ventricular developed pressure compared with 43+/-8% recovery in nonpreconditioned controls. Three cycles of preconditioning did not result in additional recovery (63+/-8%). Hearts from rabbits raised from birth in hypoxic conditions (FIO2=0.12) and subjected to 1 and 3 preconditioning cycles did not show increased recovery (68+/-8% and 65+/-5%) compared with nonpreconditioned hypoxic controls (63+/-9%), although the recovery was greater in chronically hypoxic hearts than in age-matched normoxic controls. Increasing the recovery period after the preconditioning stimulus from 10 to 30 minutes resulted in a loss of cardioprotection. Pretreatment of normoxic hearts for 30 minutes with the KATP channel blocker 5-hydroxydecanoate (300 micromol/L) completely abolished preconditioning (70+/-7% to 35+/-9%) but had no effect on nonpreconditioned hearts (40+/-8%).

CONCLUSIONS

Immature hearts normoxic from birth can be preconditioned, whereas immature hearts hypoxic from birth cannot. Preconditioning in normoxic immature hearts is associated with activation of the KATP channel.

Developmentally programmed rearrangement of T cell receptor Vgamma genes is controlled by sequences immediately upstream of the Vgamma genes

Distinct subsets of gammadelta T cells expressing different Vgamma and Vdelta chains arise in ordered waves during thymic development. In the murine Jgamma1-Cgamma1 cluster, the Vgamma3 gene segment is utilized earliest in fetal thymic development, in progenitors of dendritic epidermal T cells (DECs). The Vgamma2 gene segment predominates in the late fetal stages and beyond, in cells destined for the secondary lymphoid organs. Using transgenic TCRgamma recombination substrates, we demonstrate that this restricted Vgamma gene usage is determined by developmentally targeted gene rearrangement. We show that sequences immediately upstream of the Vgamma2 and Vgamma3 genes direct the rearrangement pattern in adult thymocytes. Thus, the choice of Vgamma gene for recombination is coordinated with distinct differentiation programs in gammadelta subsets.

Initiation of the bony epiphysis in long bones: chronology of interactions between the vascular system and the chondrocytes

Many events occur concurrently during the initiation of the secondary ossification center in the cartilaginous epiphyses of long bones. We have investigated the chronology of interactions between the vascular system and epiphyseal chondrocytes by culturing explanted heads of femurs and humeri from pre- and neonatal rabbits on the chorioallantoic membrane (CAM) of growing chick embryos. We confirmed that, on the whole, the epiphyseal cartilage was resistant to vascular invasion, whereas the physeal growth plate was resorbed. However, new CAM-derived cartilage canals occasionally penetrated through the articular surface. This caused death of those chondrocytes in the immediate vicinity of the canal but no further reaction. If explants already contained a bony epiphysis and were halved prior to culture, CAM-derived vessels were attracted to the spongiosa. From there they pushed into the uncalcified cartilage, indicating that calcification was not a prerequisite for vascular invasion. Where at least two vessels were in apposition, a new pseudo-ossification center was initiated: chondrocytes became hypertrophic and the matrix calcified. This suggests that cumulative release of diffusible factors from more than one vessel was the trigger for chondrocyte hypertrophy, which, in turn, led to the initiation of the bony epiphysis. CAM cultures thus provide an experimental model for both the quiescent angiogenesis of cartilage canal formation and the reactionary angiogenesis associated with chondrocyte hypertrophy. By exploiting the different anatomy of CAM-derived vascularity, events that occur concurrently in vivo can be specially separated in CAM culture.

A large and distinct rotation of the myosin light chain domain occurs upon muscle contraction

For more than 30 years, the fundamental goal in molecular motility has been to resolve force-generating motor protein structural changes. Although low-resolution structural studies have provided evidence for force-generating myosin rotations upon muscle activation, these studies did not resolve structural states of myosin in contracting muscle. Using electron paramagnetic resonance, we observed two distinct orientations of a spin label attached specifically to a single site on the light chain domain of myosin in relaxed scallop muscle fibers. The two probe orientations, separated by a 36 degrees +/- 5 degrees axial rotation, did not change upon muscle activation, but the distribution between them changed substantially, indicating that a fraction (17% +/- 2%) of myosin heads undergoes a large (at least 30 degrees) axial rotation of the myosin light chain domain upon force generation and muscle contraction. The resulting model helps explain why this observation has remained so elusive and provides insight into the mechanisms by which motor protein structural transitions drive molecular motility.

Effect of exposure to hypoxia from birth on aldosterone in rabbits: role of unesterified fatty acids

Hypoxia and fluid and electrolyte disturbances are serious risks to normal postnatal development. Because a decrease in inspired O2 (hypoxic hypoxia) inhibits aldosterone synthesis in the adult and aldosterone controls water and electrolyte balance, we studied adrenocortical function in rabbits exposed to normobaric normoxia or hypoxic hypoxia (fraction of inspired O2 0.09) from birth. At 21 days of age, rabbits were anesthetized, the adrenals were rapidly removed, and the adrenal capsules containing mostly zona glomerulosa cells were separated. Cells were dispersed with collagenase and studied in vitro. Hypoxia in vivo resulted in a 73% decrease in basal aldosterone release and a 86% decrease in adenosine 3',5'-cyclic monophosphate-stimulated aldosterone release in vitro. We hypothesized that increased unesterified fatty acids could be partly responsible for inhibition of aldosterone synthesis. Total serum unesterified fatty acids in hypoxic kits were significantly increased (298 +/- 14 micromol/l) compared with normoxic kits (184 +/- 31 micromol/l). When cells from hypoxic rabbits were washed with fatty acid-free albumin and studied under conditions devoid of fatty acids, aldosterone production was partially restored. Corticosterone production was not affected by washing. Washing had no effect on aldosterone synthesis by cells from normoxic rats. Finally, exposing washed zona glomerulosa cells to oleic acid (10-50 microM) inhibited aldosteronogenesis. We conclude that exposure to hypoxia from birth attenuates aldosterone production in part due to an increase in levels of unesterified fatty acid levels.