Effects of water immersion on pulmonary function in asthmatics.

Immersion induces air trapping in the lungs, as does asthma. Consequently, when using diving apparatus, asthmatics may face greater risk than non-asthmatics of pulmonary barotrauma (PBT) during ascent. We studied the pulmonary airflows and closing capacities (CC = closing volume + residual volume) in subjects with exercise-induced asthma (A, n = 12) and in healthy controls (C, n = 11) under four conditions: dry and immersed, both before and after exercise (treadmill running, non-immersed). Immersed, both C and A had significant and equivalent reductions in vital capacity, FEV1, FEV1/FVC, and FEF25%-75%. Post-exercise and immersed, pulmonary airflows deteriorated further in A but were better in C: FEV1 (A, 3.6 +/- 0.8 liter vs. 3.3 +/- 0.8 liter, P = 0.001; C, 3.9 +/- 0.5 liter vs. 4.1 +/- 0.6 liter, P = 0.006), FEF25-75% (A, 3.5 +/- 1.0 liter x s(-1) vs. 3.0 +/- 0.8 liter x s(-1). P < 0.05; C, 4.0 +/- 0.9 liter x s(-1) vs. 4.3 +/- 0.9 liter x s(-1), P < 0.05). Therefore, in contrast to C, A subjects had reduced pulmonary airflows during immersion after exercise. Furthermore, A subjects more often had no closing volume phase IV when immersed after exercise than C (P = 0.005). Interpreting the absence of phase IV as indicative of more air trapping in the asthmatics during immersion after exercise would be consistent with the reductions in airflow.

Myasthenia gravis in a collegiate football player.

A 17-yr-old Division I-AA collegiate offensive lineman developed unilateral ptosis shortly after minor head trauma during a scrimmage. The subsequent temporal profile of the ptosis, a history of a similar event lasting a short period of time 2 yr earlier, and the results of his clinical and electrophysiologic examinations established a diagnosis of very mild, generalized, antibody-negative myasthenia gravis (MG). His desire to continue playing football posed several additional management problems for which there was no published guidance. We started him on alternate-day, high-dose prednisone therapy with potassium and calcium supplementation, and allowed him to partake in conditioning but no contact. Except for residual decreased exercise tolerance, he improved symptomatically and experienced no serious adverse effects from the illness or the treatment during his first season, despite imperfect drug compliance. His MG eventually came under excellent symptomatic control, allowing initiation of a slow taper of the prednisone before his second season. Shortly thereafter, he abruptly stopped the prednisone without seeking medical advice. He continued to experience mild left ptosis and a mild decrease in intense exercise tolerance. He decided to forego his senior season of collegiate football after a bout of severe mechanical low-back pain incurred during spring football practice and limited his athletic activity thereafter to recreational sports.

A perspective on fat intake in athletes.

Performance in endurance events is dependent upon the maximal aerobic power, the percentage of that power that can be sustained and the availability of substrates (carbohydrates [CHO] and fats). The purpose of this paper is to present a perspective of recent studies that demonstrate the role of fat intake and oxidation on endurance performance. Studies have shown that fatigue is associated with reduced muscle glycogen and that increasing muscle glycogen or blood glucose prolongs performance while increasing fat and decreasing CHO decreases performance. This has led to an emphasis on CHO intake in athletes in endurance sports, which quite often leads to low caloric intake. It is well known that trained subjects have higher levels of fat oxidative capacity, which spares glycogen during endurance sports. Data from recent studies in trained athletes, who were fed iso-caloric high-fat diets (42% to 55%) that maintained adequate CHO levels, have shown an increase in endurance in both men and women when compared to diets composed of low fat intake (10% to 15%). The magnitude of the effect on endurance was significant at high percentages of maximal aerobic power and increased as the percentage of maximal aerobic power decreased. Based on this review, a baseline diet comprising 20% protein, 30% CHO and 30% fat, with the remaining 20% of the calories distributed between CHO and fat based on the intensity and duration of the sport, is recommended for discussion and future research.

The effects of varying dietary fat on performance and metabolism in trained male and female runners.

OBJECTIVES: Low dietary fat intake has become the diet of choice for many athletes. Recent studies in animals and humans suggest that a high fat diet may increase VO2max and endurance. We studied the effects of a low, medium and high fat diet on performance and metabolism in runners. METHODS: Twelve male and 13 female runners (42 miles/week) ate diets of 16% and 31% fat for four weeks. Six males and six females increased their fat intakes to 44%. All diets were designed to be isocaloric. Endurance and VO2max were tested at the end of each diet. Plasma levels of lactate, pyruvate, glucose, glycerol, and triglycerides were measured before and after the VO2max and endurance runs. Free fatty acids were measured during the VO2max and endurance runs. RESULTS: Runners on the low fat diet ate 19% fewer calories than on the medium or high fat diets. Body weight, percent body fat (males=71 kg and 16%; females=57 kg and 19%), VO2max and anaerobic power were not affected by the level of dietary fat. Endurance time increased from the low fat to medium fat diet by 14%. No differences were seen in plasma lactate, glucose, glycerol, triglycerides and fatty acids when comparing the low versus the medium fat diet. Subjects who increased dietary fat to 44% had higher plasma pyruvate (46%) and lower lactate levels (39%) after the endurance run. CONCLUSION: These results suggest that runners on a low fat diet consume fewer calories and have reduced endurance performance than on a medium or high fat diet. A high fat diet, providing sufficient total calories, does not compromise anaerobic power.

Muscle structure with low- and high-fat diets in well-trained male runners.

Endurance capacity, maximal oxygen uptake capacity (VO2max) and quantitative muscle ultrastructural composition was analyzed in 7 well-trained male runners (mean age 37.1 years, mean VO2max 60 ml/min/kg) after a one month period of a low-fat diet (dietary fat intake 18.4% and a similar period of a high-fat diet (dietary fat intake 40.6%). Between these two interventional periods a washout period of one month was interspersed in which the nutritional fat content was approx. 32%; close to the average American Diet. During all three periods protein content of the nutrition was kept nearly constant at 15%. After the high-fat diet time to exhaustion in the endurance test increased significantly by 21% while VO2max remained unchanged. Muscle mitochondrial volume density remained unchanged while the intramyocellular fat content increased by 60%. Due to large interindividual differences in this variable this difference did not become statistically significant. While some 20% of the mitochondria are located in a subsarcolemmal location, only 10% of the lipid stores are associated with these mitochondria. Less than 2% of the mitochondrial outer surface are in contact with lipid droplets whereas 25-35% of the lipid surface is in contact with mitochondria. None of these variables is significantly altered after a high-fat diet. It is concluded that the change in endurance capacity of the subjects cannot be explained based on the structural changes observed in skeletal muscle tissue. This may be related to methodological problems associated with the determination of intramyocellular fat content.

Prospective evaluation of the Ottawa Ankle Rules in a university sports medicine center. With a modification to increase specificity for identifying malleolar fractures.

In a sports medicine center, we prospectively evaluated the Ottawa Ankle Rules over 1 year for their ability to identify clinically significant ankle and midfoot fractures and to reduce the need for radiography. We also developed a modification to improve specificity for malleolar fracture identification. Patients with acute ankle injuries (< or = 10 days old) had the rules applied and then had radiographs taken. Sensitivity, specificity, and the potential reduction in the use of radiography were calculated for the Ottawa Ankle Rules in 132 patients and for the new "Buffalo" rule in 78 of these patients. There were 11 clinically significant fractures (fracture rate, 8.3% per year). In these 132 patients, the Ottawa Ankle Rules would have reduced the need for radiography by 34%, without any fractures being missed (sensitivity 100%, specificity 37%). In 78 patients, the specificity for malleolar fracture for the new rule was significantly greater than that of the Ottawa Ankle Rules malleolar rule (59% versus 42%), sensitivity remained 100%, and the potential reduction in the need for radiography (54%) was significantly greater. The Ottawa Ankle Rules could significantly reduce the need for radiography in patients with acute ankle and midfoot injuries in this setting without missing clinically significant fractures. The Buffalo modification could improve specificity for malleolar fractures without sacrificing sensitivity and could significantly reduce the need for radiography.

The association of cardiac dystrophin with myofibrils/Z-disc regions in cardiac muscle suggests a novel role in the contractile apparatus.

Dystrophin serves a variety of roles at the cell membrane through its associations, and defects in the dystrophin gene can give rise to muscular dystrophy and genetic cardiomyopathy. We investigated localization of cardiac dystrophin to determine potential intracellular sites of association. Subcellular fractionation revealed that while the majority of dystrophin was associated with the sarcolemma, about 35% of the 427-kDa form of dystrophin was present in the myofibrils. The dystrophin homolog utrophin was detectable only in the sarcolemmal membrane and was absent from the myofibrils as were other sarcolemmal glycoproteins such as adhalin and the sodium-calcium exchanger. Extraction of myofibrils with KC1 and detergents could not solubilize dystrophin. Dystrophin could only be dissociated from the myofibrillar protein complex in 5 M urea followed by sucrose density gradient centrifugation where it co-fractionated with one of two distinctly sedimenting peaks of actin. Immunoelectron microscopy of intracellular regions of cardiac muscle revealed a selective labeling of Z-discs by hystrophin antibodies. In the genetically determined cardiomyopathic hamster, strain CHF 147, the time course of development of cardiac insufficiency correlated with an overall 75% loss of myofibrillar dystrophin. These findings collectively show that a significant pool of the 427-kDa form of cardiac dystrophin was specifically associated with the contractile apparatus at the Z-discs, and its loss correlated with progression to cardiac insufficiency in genetic cardiomyopathy. The loss of distinct cellular pools of dystrophin may contribute to the tissue-specific pathophysiology in muscular dystrophy.

The role of dietary fat on performance, metabolism, and health.

This paper presents a model to evaluate the nutritional status of trained athletes based on work in our laboratory as well as others. The model proposes that substrate use is set by the muscle fibers recruited, based on the exercise intensity. Second, the substrate available is primarily determined by the intramuscular stores. In trained athletes, intramuscular fat plays an important role in metabolism at exercise intensities as high as 80% of maximal aerobic power. Based on these factors, increasing the fat in the diet (while maintaining adequate intramuscular glycogen) increases VO2max and intramuscular stores of fat (presumably due to increased mitochondrial volume). These two factors result in a significant increase in the time to exhaustion at set levels of exercise (endurance). It also appears that fatigue is associated with depletion of either glycogen or fat. These conclusions hold true for athletes on diets where sufficient calories are taken in to meet demands and for exercise levels below 80% of VO2max, where primarily slow-twitch oxidative fibers are used. These data may not apply in exercise where predominantly fast-twitch fibers are used. Also, these data do not apply to runners eating a hypocaloric diet, where reducing the percentage of carbohydrates may compromise their glycogen stores. It would appear that the fat in the diet can be increased to a very high level without compromising the cardiovascular or immune systems of athletes. Moreover, it can be proposed that these data could be applied to sedentary persons, as long as they are isocaloric. This would imply that the fat consumed in the diet would be used in the muscle, as in the runners, although at a lower level. Thus, the dietary intake should be matched in both total calories and percentage of fats and carbohydrates to calories consumed by daily activity. It should be cautioned that if glycogen and fat stores are compromised, protein resynthesis is inhibited and loss of muscle mass may result. This has a negative effect on the athlete's ability to perform at high levels.

Regulation of dihydropyridine and ryanodine receptor gene expression in skeletal muscle. Role of nerve, protein kinase C, and cAMP pathways.

The dihydropyridine (DHP) and ryanodine (RY) receptors play a critical role in depolarization-induced calcium release in skeletal muscle, yet the factors which govern their expression remain unknown. We investigated the roles of electrical activity and trophic factors in the regulation of the genes encoding the alpha 1, alpha 2, and beta subunits of the DHP receptor as well as the RY receptor in rat skeletal muscle in vivo. Muscle paralysis, induced by denervation, had no effect on the DHP receptor mRNA levels while the RY receptor mRNA was decreased. In contrast, chronic superfusion of tetrodotoxin onto the sciatic nerve resulted in a marked increase in mRNA levels and transcriptional activity of both DHP and RY receptor genes. Since nerve can induce changes in second messenger pathways which modulate muscle gene expression, we attempted to identify factors which regulate DHP and RY receptor expression using cultured myotubes. Elevated cAMP levels specifically inhibited the expression of RY receptor mRNA while 12-O-tetradecanoylphorbol-13-acetate, an activator of protein kinase C, increased the transcripts encoding the RY receptor and the alpha 1 subunit of the DHP receptor. Changes in the level of mRNAs were paralleled by altered receptor numbers. Neither cAMP nor protein kinase C altered transcriptional activity of the DHP and RY receptor genes. These results demonstrate that neural factor(s) regulate DHP and RY receptor mRNA levels in vivo via transcriptional mechanisms while protein kinase C and cAMP can modulate DHP and RY receptor transcript levels by a transcription-independent process.

Temporal differences in the induction of dihydropyridine receptor subunits and ryanodine receptors during skeletal muscle development.

The expression of the dihydropyridine (DHP) and ryanodine receptors in skeletal muscle was investigated during development of rat myotubes in culture as well as during embryonic and postnatal development in the rat. Through the use of specific gene probes, antibodies and radioligand binding ([3H]PN 200-110 (DHP) and [3H]ryanodine), we identified a significant difference between the time course of appearance of the DHP receptor and the ryanodine receptor during muscle development. Although the number of DHP receptors dramatically increased at early stages of development (up to day 7 in tissue culture and day 20 postnatal), increase in the ryanodine receptor density occurred comparatively later at day 10 in culture and day 30 postnatal. This process was associated with parallel changes in the expression of the mRNA encoding the alpha 1, alpha 2, and beta subunits of the DHP receptor and the skeletal muscle ryanodine receptor. The genes encoding the DHP receptor subunits were activated in a temporally distinct transcript appeared and plateaued first, at the onset of myoblast fusion and day 16 embryonic. This was followed closely by an increase in expression of the mRNAs for alpha 1 and alpha 2 subunits which coincided with the sharp rise in the DHP receptor density. Ryanodine receptor gene expression was induced well after the DHP receptor gene expression had plateaued. The temporal appearance of the polypeptides comprising the DHP receptor subunits and the ryanodine receptor paralleled the induction of the genes encoding these receptors. These results imply that gene expression is a major mechanism that contributes to the regulation of DHP and ryanodine receptor numbers during muscle development. The temporal differences in the induction of the genes encoding the DHP receptor subunits and the ryanodine receptor suggests that these genes are under the control of distinct endogenous factors. These differences in expression of the DHP receptor and the ryanodine receptor may contribute to the different mechanisms of excitation-contraction coupling in immature versus adult skeletal muscle.

Effect of dietary fat on metabolic adjustments to maximal VO2 and endurance in runners.

The present study examined the effects of dietary manipulations on six trained runners. The percent energy contributions from carbohydrate, fat, and protein were 61/24/14, 50/38/12, and 73/15/12 for the normal (N), fat (F), and carbohydrate (C) diets, respectively. Expiratory gases and blood responses to a maximum (VO2max) and a prolonged treadmill run were determined following 7 d on each diet. Free fatty acids (FFA), triglycerides, glycerol, glucose, and lactate were measured. Dietary assessment of subjects' N diet indicated that they were consuming approximately 700 kcal.d-1 less than estimated daily expenditures. Running time to exhaustion was greatest after the F diet (91.2 +/- 9.5 min, P < 0.05) as compared with the C (75.8 +/- 7.6 min, P < 0.05) and N (69.3 +/- 7.2 min, P < 0.05) diets. VO2max was also higher on the F diet (66.4 +/- 2.7 ml.kg-1 x min-1, P < 0.05) as compared with the C (59.6 +/- 2.8 ml.kg-1 x min-1, P < 0.05) and N (63.7 +/- 2.6 ml.kg-1 x min-1, P < 0.05) diets. Plasma FFA levels were higher (P < 0.05) and glycerol levels were lower (P < 0.05) during the F diet than during the C and N diets. Other biochemical measures did not differ significantly among diets. These data suggest that increased availability of FFA, consequent to the F diet, may provide for enhanced oxidative potential as evidenced by an increase in VO2max and running time. This implies that restriction of dietary fat may be detrimental to endurance performance.

A 60 kDa polypeptide of skeletal-muscle sarcoplasmic reticulum is a calmodulin-dependent protein kinase that associates with and phosphorylates several membrane proteins.

Activation of a calmodulin (CaM)-dependent protein kinase associated with rabbit skeletal-muscle sarcoplasmic reticulum (SR) results in the phosphorylation of polypeptides of 450, 360, 165, 105, 89, 60, 34 and 20 kDa. Radioligand-binding studies indicated that a membrane-bound 60 kDa polypeptide contained both CaM- and ATP-binding domains. Under renaturing conditions on nitrocellulose blots, the 60 kDa polypeptide of the membrane exhibited CaM-dependent autophosphorylation activity, suggesting that it was the CaM-dependent protein kinase of SR. Ca2+/CaM-independent autophosphorylation of polypeptides of 62 and 45 kDa was found to occur in the light SR, whereas the Ca2+/CaM-dependent autophosphorylation activity was enriched in the heavy SR. Both these kinase activities were absent from transverse tubules, although these membranes were enriched in CaM-binding polypeptides of 160, 100 and 80 kDa. In the absence of Ca2+, CaM bound to a 33 kDa polypeptide of the membrane. The purified ryanodine receptor was not phosphorylated by the purified CaM kinase, although it was a substrate for protein kinase C. Affinity-purified antibodies to brain CaM kinase II cross-reacted with the 60 kDa polypeptide in Western blots and immunoprecipitated the 60 kDa polypeptide, along with the 360, 105, 89, 34 and 20 kDa phosphoproteins, from Nonidet-P-40-solubilized SR membranes. Antibodies raised against the 60 kDa kinase polypeptide did not cross-react with the other phosphoproteins, suggesting that these polypeptides were distinct and unrelated. Subcellular distribution of the 60 kDa kinase indicated the specific association of the polypeptide with the junctional-face membrane of SR. The CaM-dependent incorporation of 32P into various membrane proteins was inhibited by the CaM kinase II fragment (290-309), with an IC50 value of 2 nM for the inhibition of incorporation into the 60 kDa kinase polypeptide. Recent studies [Wang and Best (1992) Nature (London) 359, 739-741] have shown that a CaM kinase activity intrinsic to the membrane can inactivate the Ca(2+)-release channel of skeletal muscle SR. Since our results demonstrate that the 60 kDa polypeptide of SR is a CaM-dependent protein kinase, we suggest that this kinase, through its associations, may be responsible for gating the Ca(2+)-release channel.

Structure, stability, and receptor interaction of cholera toxin as studied by Fourier-transform infrared spectroscopy.

The structure and thermal stability of isolated B and A subunits of cholera toxin, as well as the interaction of the B subunit with a ganglioside GM1 receptor, were studied by Fourier-transform infrared spectroscopy. The B subunit of the toxin is highly folded; its secondary structure consists predominantly of beta-sheets. The temperature dependence of the infrared spectrum indicates that the B subunit undergoes thermal unfolding in the temperature range between approximately 66 and 78 degrees C. Binding to the ganglioside GM1 receptor or to its oligosaccharide moiety results in only marginal, if any, change in the secondary structure of the B subunit; however, the receptor-associated subunit does show a markedly increased thermal stability. The secondary structure of the enzymatically active A subunit is less ordered and much less stable than that of the B subunit. The relatively loose folding of the A subunit is likely to be of importance for the effective membrane translocation of this subunit.