PubMed Health⌕ Search

Biomedical subjects

M K Connor

Publications and source records attributed to M K Connor.

15 recordsLinked to original sources
PubMed2001

Contractile activity-induced transcriptional activation of cytochrome C involves Sp1 and is proportional to mitochondrial ATP synthesis in C2C12 muscle cells.

Contractile activity induces adaptations in the expression of genes encoding skeletal muscle mitochondrial proteins; however, the putative signals responsible for these adaptations remain unknown. We used electrical stimulation (5 Hz, 65 V) of C2C12 muscle cells in culture to define some of the mechanisms involved in contractile activity-induced changes in cytochrome c gene expression. Chronic contractile activity (4 days, 3 h/day) augmented cytochrome c mRNA by 1.6-fold above control cells. This was likely mediated by increases in transcriptional activation, because cells transfected with full-length (-726 base pairs) or minimal (-66 base pairs) cytochrome c promoter/chloramphenicol acetyltransferase reporter constructs demonstrated contractile activity-induced 1.5-1.7-fold increases in the absence of contractile activity-induced increases in mRNA stability. Transcriptional activation of the -726 promoter was abolished when muscle contraction was inhibited at various subcellular locations by pretreatment with either the Na(+) channel blocker tetrodotoxin, the intracellular Ca(2+) chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester, or the myosin ATPase inhibitor 2,3-butanedione monoxime. It was further reduced in unstimulated cells when mitochondrial ATP synthesis was impaired using the uncoupler 2,4-dinitrophenol. Because the contractile activity-induced response was evident within the minimal promoter, electromobility shift assays performed within the first intron (+75 to +104 base pairs) containing Sp1 sites revealed an elevated DNA binding in response to contractile activity. This was paralleled by increases in Sp1 protein levels. Sp1 overexpression studies also led to increases in cytochrome c transactivation and mRNA levels. These data suggest that variations in the rate of mitochondrial ATP synthesis are important in determining cytochrome c gene expression in muscle cells and that this is mediated, in part, by Sp1-induced increases in cytochrome c transcription.

Animals↗
PubMed2000

Serum vitamin C levels and use of health care resources for wheezing episodes.

BACKGROUND: Evidence suggests that the antioxidant vitamin C may play a role in lung function and wheezing, although the data are limited to laboratory evaluation of pulmonary function. OBJECTIVE: To examine the relationship among serum vitamin C levels, wheezing episodes, and use of health care services. METHODS: Analysis of adult subjects (aged > or = 17 years) surveyed in the third National Health and Nutrition Examination Survey (1988-1994) (n = 19,760), including measurements of serum vitamin C levels and self-reports of wheezing episodes, ambulatory health care visits, and overnight hospitalizations for wheezing. RESULTS: A large proportion of individuals (2377/19,760 [12.0%]) have received a diagnosis of asthma, chronic bronchitis, or emphysema. Among 874 individuals having an ambulatory visit for wheezing, 408 (46.7%) did not have a diagnosed respiratory conditions. Similarly, among 159 individuals hospitalized for wheezing, 61 (38.4%) did not have a diagnosed respiratory condition. Serum vitamin C level had no significant relationship with reported diagnosis of respiratory conditions, episodes of wheezing, or use of health care services for wheezing. In a model computed only with individuals with low or high serum vitamin C levels, after adjustment for potential confounders, no statistically significant relationship was found between serum vitamin C levels and ambulatory care (odds ratio, 0.78; 95% confidence interval, 0.58-1.05) or hospitalization for wheezing episodes (odds ratio, 1.21; 95% confidence interval, 0.67-2.21). CONCLUSIONS: Serum vitamin C levels do not appear to be a marker for use of health care services for wheezing. Future investigations of the role of antioxidants in managing respiratory conditions should focus on the clinically important outcomes of health care use.

Adult↗
PubMed2000

Tom20-mediated mitochondrial protein import in muscle cells during differentiation.

Mitochondrial biogenesis is accompanied by an increased expression of components of the protein import machinery, as well as increased import of proteins destined for the matrix. We evaluated the role of the outer membrane receptor Tom20 by varying its expression and measuring changes in the import of malate dehydrogenase (MDH) in differentiating C2C12 muscle cells. Cells transfected with Tom20 had levels that were twofold higher than in control cells. Labeling of cells followed by immunoprecipitation of MDH revealed equivalent increases in MDH import. This parallelism between import rate and Tom20 levels was also evident as a result of thyroid hormone treatment. Using antisense oligodeoxynucleotides, we inhibited Tom20 expression by 40%, resulting in 40-60% reductions in MDH import. In vitro assays also revealed that import into the matrix was more sensitive to Tom20 inhibition than import into the outer membrane. These data indicate a close relationship between induced changes in Tom20 and the import of a matrix protein, suggesting that Tom20 is involved in determining the kinetics of import. However, this relationship was dissociated during normal differentiation, since the expression of Tom20 remained relatively constant, whereas imported MDH increased 12-fold. Thus Tom20 is important in determining import during organelle biogenesis, but other mechanisms (e.g., intramitochondrial protein degradation or nuclear transcription) likely also play a role in establishing the final mitochondrial phenotype during normal muscle differentiation.

Cell Differentiation↗
PubMed2000

Effect of contractile activity on protein turnover in skeletal muscle mitochondrial subfractions.

To determine the role of intramitochondrial protein synthesis (PS) and degradation (PD) in contractile activity-induced mitochondrial biogenesis, we evaluated rates of [(35)S]methionine incorporation into protein in isolated rat muscle subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria. Rates of PS ranged from 47 to 125% greater (P < 0.05) in IMF compared with SS mitochondria. Intense, acute in situ contractile activity (10 Hz, 5 min) of fast-twitch gastrocnemius muscle resulted in a 50% decrease in PS (P < 0.05) in SS but not IMF mitochondria. Recovery, or continued contractile activity (55 min), reestablished PS in SS mitochondria. In contrast, PS was not affected in either SS or IMF mitochondria after prolonged (60-min) contractile activity in the presence or absence of a recovery period. PD was not influenced by 5 min of contractile activity in the presence or absence of recovery but was reduced after 60 min of contractions followed by recovery. Chronic stimulation (10 Hz, 3 h/day, 14 days) increased muscle cytochrome-c oxidase activity by 2.2-fold but reduced PS in IMF mitochondria by 29% (P < 0.05; n = 4). PS in SS mitochondria and PD in both subfractions were not changed by chronic stimulation. Thus acute contractile activity exerts differential effects on protein turnover in IMF and SS mitochondria, and it appears that intramitochondrial PS does not limit the extent of chronic contractile activity-induced mitochondrial biogenesis.

Animals↗
PubMed2000

Challenges to academic family medicine in the current health care environment.

BACKGROUND: Changes in health care delivery and funding have placed strains on academic medical centers' ability to meet their multiple missions. To gain insight into how this new academic landscape is affecting academic primary care, this study examined the current status and perceived challenges at nine departments of family medicine at allopathic and osteopathic medical schools. METHODS: Site visits were made to nine academic departments of family medicine where key informant interviews were conducted with several individuals in key leadership positions. Sites were chosen to maximize diversity among departments along a variety of factors, such as location, size, mission, and type of school (private versus public). Interviews were transcribed and analyzed by a three-person multidisciplinary team for key themes. RESULTS: Analysis of interviews revealed five major challenges for academic departments of family medicine: 1) adjusting to new clinical demands in the academic health center, 2) organizing and administering new initiatives in community-based education, 3) recruiting and retaining faculty, 4) developing and maintaining research capacity, and 5) serving multiple missions (education, clinical care, and academic pursuits) in times of financial restraint. CONCLUSIONS: Significant challenges face academic departments of family medicine. The success or failure of departments of family medicine to meet these challenges could serve as a bellwether for how primary care fits into the future overall scheme of academic health centers.

Conflict, Psychological↗
PubMed2000

Assembly of the cellular powerhouse: current issues in muscle mitochondrial biogenesis.

Mitochondrial biogenesis occurs in muscle in response to chronic exercise, resulting in fatigue resistance. The assembly of the organelle is initiated by contraction-induced signals, which lead to the transcriptional activation of nuclear genes. This is accompanied by alterations in mRNA stability, as well as increases in protein import and mitochondrial DNA copy number, leading to a greater muscle mitochondrial content.

Exercise↗
PubMed1999

Cytochrome c transcriptional activation and mRNA stability during contractile activity in skeletal muscle.

We evaluated contractile activity-induced alterations in cytochrome c transcriptional activation and mRNA stability with unilateral chronic stimulation (10 Hz, 3 h/day) of the rat tibialis anterior (TA) muscle for 1, 2, 3, 4, 5, and 7 days (n = 3-11/group). Transcriptional activation was assessed by direct plasmid DNA injection into the TA with a chloramphenicol acetyltransferase (CAT) reporter gene linked to 326 bp of the cytochrome c promoter. Cytochrome c mRNA in stimulated muscles increased by 1.3- to 1. 7-fold above control between 1 and 7 days. Cytochrome c protein was increased after 5 days of stimulation to reach levels that were 1. 9-fold higher than control by 7 days. Cytochrome c mRNA stability, determined with an in vitro decay assay, was greater in stimulated TA than in control between 2 and 4 days, likely mediated by the induction of a cytosolic factor. In contrast, cytochrome c transcriptional activation was elevated only after 5 days of stimulation when mRNA stability had returned to control levels. Thus the contractile activity-induced increase in cytochrome c mRNA was due to an early increase in mRNA stability, followed by an elevation in transcriptional activation, leading to an eventual increase in cytochrome c protein levels.

Animals↗
PubMed1999

Survey of clinical pharmacists' knowledge of appropriateness of antimicrobial therapy for upper respiratory infections and acute bronchitis.

We conducted a survey to assess clinical pharmacists' recommendation of antibiotics for upper respiratory infections (URIs) and acute bronchitis. A random sample of 752 members of the American College of Clinical Pharmacy were mailed a multiple-choice survey that presented four examples consistent with clinical symptoms of the two disorders. Respondents were asked what treatment they would recommend for each example. The response rate was 59%. Pharmacists recommended antibiotics for the treatment of both URIs and acute bronchitis significantly more if patients' symptoms included discolored discharge or sputum as opposed to clear discharge. Those who were board certified were less likely than nonboard-certified pharmacists to recommend antibiotics for URIs with discolored discharge. Pharmacists who specialized in either ambulatory care or infectious disease were less likely than those in other specialties to recommend antibiotics for acute bronchitis with discolored sputum. Clinical pharmacists are similar to patients and physicians in their belief that antibiotics are appropriate for URIs and acute bronchitis with discolored discharge. Considering the role that pharmacists play as clinical consultants to physicians, greater efforts should be made to educate them regarding appropriate prescription of antibiotics.

Acute Disease↗
PubMed1998

Effect of microgravity on the expression of mitochondrial enzymes in rat cardiac and skeletal muscles.

The purpose of this study was to examine the expression of nuclear and mitochondrial genes in cardiac and skeletal muscle (triceps brachii) in response to short-duration microgravity exposure. Six adult male rats were exposed to microgravity for 6 days and were compared with six ground-based control animals. We observed a significant 32% increase in heart malate dehydrogenase (MDH) enzyme activity, which was accompanied by a 62% elevation in heart MDH mRNA levels after microgravity exposure. Despite modest elevations in the mRNAs encoding subunits III, IV, and VIc as well as a 2.2-fold higher subunit IV protein content after exposure to microgravity, heart cytochrome c oxidase (CytOx) enzyme activity remained unchanged. In skeletal muscle, MDH expression was unaffected by microgravity, but CytOx activity was significantly reduced 41% by microgravity, whereas subunit III, IV, and VIc mRNA levels and subunit IV protein levels were unaltered. Thus tissue-specific (i.e., heart vs. skeletal muscle) differences exist in the regulation of nuclear-encoded mitochondrial proteins in response to microgravity. In addition, the expression of nuclear-encoded proteins such as CytOx subunit IV and expression of MDH are differentially regulated within a tissue. Our data also illustrate that the heart undergoes previously unidentified mitochondrial adaptations in response to short-term microgravity conditions more dramatic than those evident in skeletal muscle. Further studies evaluating the functional consequences of these adaptations in the heart, as well as those designed to measure protein turnover, are warranted in response to microgravity.

Adaptation, Physiological↗
PubMed1996

Tissue-specific stability of nuclear- and mitochondrially encoded mRNAs.

Steady-state levels of mRNAs encoding mitochondrial proteins are drastically different among tissues. We evaluated tissue-specific variations in mRNA stability by comparing rates of mRNA decay in liver, heart, and muscle following the inhibition of transcription. Rates of decline of the mRNAs encoding delta-aminolevulinate synthase (ALAs), cytochrome c oxidase subunit VIc (nuclear-encoded), and subunit III (mitochondrially encoded) in heart, liver, and muscle for 6 h following transcription inhibition with actinomycin D or ethidium bromide were measured. Subunit VIc mRNA levels were least stable in liver (t1/2 = 2.4 h), slightly greater in heart (t1/2 = 3.3 h), and very stable in skeletal muscle. Similarly, ALAs mRNA exhibited a t1/2 of 41 min in liver, but this was markedly increased to approximately 11-14 h in heart and skeletal muscle. In contrast, subunit III was least stable in heart (t1/2 = 2.1 h), somewhat more stable in liver (t1/2 = 3.8 h), but no decline in subunit III mRNA levels occurred in muscle following the inhibition of transcription. Thus, muscle, heart, and liver possess tissue-specific mechanisms which control the stability of mRNAs encoding mitochondrial proteins. In addition, the coordinated expression of subunit III and VIc mRNAs is different tissues is partly due to parallel rates of mRNA turnover. This suggests the presence of intra- and extramitochondrial factors within a tissue which regulate the stability of specific mRNAs in a similar manner.

5-Aminolevulinate Synthetase↗
PubMed1996

Dystrophin, vinculin, and aciculin in skeletal muscle subject to chronic use and disuse.

Dystrophin is a subsarcolemmal protein that interacts with cytoskeletal actin and a glycoprotein complex in the plasma membrane. One potential function of dystrophin is its ability to stabilize the sarcolemmal membrane during muscle contraction. We hypothesized 1) that chronic muscle use and disuse would alter the expression of dystrophin as a compensatory mechanism designed to prevent muscle damage, and 2) that other subsarcolemmal cytoskeletal proteins (vinculin, M-vinculin, aciculin 60/63 kDa) that colocalize with dystrophin in muscle adherens junctions would be changed in parallel. Chronic muscle use induced by voluntary running or 10-Hz chronic stimulation did not alter dystrophin levels in rat muscle. In contrast, muscle disuse induced by 6 d of microgravity, or 7 and 21 d of denervation, increased dystrophin levels by 1.8-, 1.9- and 3.2-fold, respectively. Thus, this increase in dystrophin levels appears to be dependent on the duration of muscle disuse, independent of the presence of the nerve. Denervation also induced 3.3-fold increases in vinculin and aciculin 60 kDa, in parallel with dystrophin. However, in contrast to its effects on dystrophin, chronic stimulation increased the levels of vinculin and aciculin 60 kDa by 3.4- and 6.4-fold, respectively. Thus, both the removal and the augmentation of muscle activity resulted in increases of these two cytoskeletal proteins. The data indicate that the concentrations of these proteins are independently regulated. They further indicate that chronic muscle use is not a stimulus for the induction of dystrophin levels, suggesting that normal levels are sufficient for the protective effect on the sarcolemma that dystrophin may confer. The results reveal an interesting area of muscle plasticity, and the adaptation observed may have profound implications for the structure and function of skeletal muscle responding to changes in contractile activity.

Adaptation, Physiological↗
PubMed1995

Expression of stress proteins and mitochondrial chaperonins in chronically stimulated skeletal muscle.

Molecular chaperones and cytosolic stress proteins are actively involved in the stabilization, import and refolding of precursor proteins into mitochondria. The purpose of the present study was to evaluate the relationship between mitochondrial content under steady-state conditions, and during the induction of organelle biogenesis, with the expression of stress proteins and mitochondrial chaperonins. A comparison of steady-state levels of mitochondrial enzyme activity [cytochrome c oxidase (CYTOX)] with chaperonin levels [the heat-shock protein HSP60, the glucose-regulated protein GRP75 (mtHSP70)] in striated muscles possessing a wide range of oxidative capacities revealed a proportional expression between the two. This relationship was disrupted by chronic contractile activity brought about by 10 days of 10 Hz stimulation of the tibialis anterior (TA) muscle, which induced 2.4-fold increases in CYTOX activity, but 3.2- and 9.3-fold increases in HSP60 and GRP75 respectively. The inducible stress protein HSP70i was detected at low levels in control TA muscle, and was increased 9.6-fold by chronic contractile activity, to values comparable with those found in the unstressed soleus muscle. This increase occurred in the absence of changes in type I MHC levels, indicating independent regulation of these genes. Despite the increases in HSP60 and HSP70i proteins, contractile activity did not alter their respective mRNA levels, illustrating post-transcriptional mechanisms of gene regulation during contractile activity. In contrast, the mRNA levels encoding the co-chaperonin CPN10 were increased 3.3-fold by contractile activity. Thus, the expression of individual mitochondrial chaperonins is independently regulated and uncoordinated. The extent of the induction of these stress proteins and chaperonins by contractile activity exceeded that of membrane enzymes (e.g. CYTOX). It remains to be determined whether this marked induction of proteins comprising part of the protein import machinery is beneficial for the translocation of enzyme precursors into the mitochondria during conditions of accelerated biogenesis.

Animals↗
PubMed1994

Mitochondrial biogenesis in striated muscle.

Mitochondrial biogenesis (synthesis) has been observed to occur in skeletal muscle in response to chronic use. It also occurs in cardiac muscle during growth and hypertrophy, and it may be impaired during the aging process. This review summarizes the literature on the processes of mitochondrial biogenesis at the biochemical and molecular levels, with particular reference to striated muscles. Mitochondrial biogenesis involves the expression of nuclear and mitochondrial genes and the coordination of these two genomes, the synthesis of proteins and phospholipids and their import into the organelle, and the incorporation of these lipids and proteins into their appropriate locations within the matrix, inner or outer membranes. The emphasis is on the regulation of these events, with information derived in part from other cellular systems. Although descriptions of mitochondrial content changes in heart and skeletal muscle during altered physiological states are plentiful, much work is needed at the molecular level to investigate the regulatory processes involved. A knowledge of biochemical and molecular biology techniques is essential for continued progress in the field. This is a promising area, and potential new avenues for future research are suggested.

Animals↗
PubMed1986

Future Fit: a cardiovascular health education and fitness project in an after-school setting.

Future Fit was developed to provide a low cost, heart health education and fitness program that could be incorporated readily into existing after-school programs with minimal teacher training and nominal expenditures for equipment and supplies. Participants in the 12-week demonstration project were 55 third and fourth grade students enrolled in after-school programs at four sites, randomly assigned to experimental and control conditions. Results indicated significant knowledge gains and changes in knowledge, attitude, and behavior at home. These outcomes suggest health and fitness programming in the after-school setting can be an effective complement to the education provided within the school setting.

Attitude to Health↗