Biomedical subjects

M E Houston

Publications and source records attributed to M E Houston.

At least 55 records · Page 3Linked to original sources

PubMed1989

Intramuscular comparison of myosin isozymes and light chains in rat extensor digitorum longus muscle.

Complete muscle cross sections were obtained from the proximal and distal third regions of ten rat extensor digitorum longus muscles. Electrophoretic methods were then used to quantify the various myosin isozymes and light chains in each muscle specimen. The results demonstrated that the relative distribution of the various myosin isozyme and light chain variables do not vary significantly between the two sampling regions.

Animals↗

PubMed1989

Muscle energetics during prolonged cycling after exercise hypervolemia.

This study examined the question of whether increases in plasma volume (hypervolemia) induced through exercise affect muscle substrate utilization and muscle bioenergetics during prolonged heavy effort. Six untrained males (19-24 yr) were studied before and after 3 consecutive days of cycling (2 h/day at 65% of peak O2 consumption) performed in a cool environment (22-23 degrees C, 25-35% relative humidity). This protocol resulted in a 21.2% increase in plasma volume (P less than 0.05). During exercise no difference was found in the blood concentrations of glucose, lactate, and plasma free fatty acids at either 30, 60, 90, or 120 min of exercise before and after the hypervolemia. In contrast, blood alanine was higher (P less than 0.05) during both rest and exercise with hypervolemia. Measurement of muscle samples extracted by biopsy from the vastus lateralis muscle at rest and at 60 and 120 min of exercise indicated no effect of training on high-energy phosphate metabolism (ATP, ADP, creatine phosphate, creatine) or on selected glycolytic intermediate concentrations (glucose 1-phosphate, glucose 6-phosphate, fructose 6-phosphate, lactate). In contrast, training resulted in higher (P less than 0.05) muscle glucose and muscle glycogen concentrations. These changes were accompanied by blunting of the exercise-induced increase (P less than 0.05) in both blood epinephrine and norepinephrine concentrations. Plasma glucagon and serum insulin were not affected by the training. The results indicate that exercise-induced hypervolemia did not alter muscle energy homeostasis. The reduction in muscle glycogen utilization appears to be an early adaptive response to training mediated either by an increase in blood glucose utilization or a decrease in anaerobic glycolysis.

Adult↗

PubMed1988

Mechanical measures during maximal velocity knee extension exercise and their relation to fibre composition of the human vastus lateralis muscle.

A method for measuring the maximal velocity of knee extension exercise is described using a very light lever arm. Instrumentation of the lever arm with a potentiometer and accelerometer also allows for the measurement of peak acceleration, time to peak acceleration, the average rate of development of acceleration (jerk) and peak torque. With this apparatus and surface electromyography, electromechanical delay (EMD) was also determined. This apparatus was tested using 17 female and 10 male subjects, and the measures obtained were related to the percentage of fast twitch fibres (% FT) and the relative area of fast twitch fibres (% FTA) in the vastus lateralis determined from duplicate muscle biopsy samples. Peak velocity of unloaded knee extension averaged 12.1 +/- 1.2 and 12.2 +/- 1.7 rad.s-1 for females and males, respectively, and were not significantly different. As well, peak acceleration, time to peak acceleration jerk and EMD values were not significantly different between the female and male subjects, but the mean peak torque for the female subjects (73.5 +/- 14.7 N.m) was significantly lower than that for the males (98.4 +/- 31.5 N.m). Peak acceleration was significantly correlated with %FT (r = 0.40, P = 0.04) for the total subject population. None of the other measures was significantly related to either %FT or %FTA for the male and female subjects or the combined population of subjects.

Biomechanical Phenomena↗

PubMed1988

Myosin light chains in regenerating rat skeletal muscle following chronic, low-frequency, electrical stimulation.

Ten days of chronic, low-frequency, electrical stimulation of regenerating rat extensor digitorum longus muscle causes an increase in the percentage of slow, phosphorylatable myosin light chains with a complementary decrease in the total fast light chain content. This altered light chain expression is similar to that observed when electrical stimulation is applied to a developing muscle in vivo.

Animals↗

PubMed1988

Myosin light chain phosphorylation and contractile performance of human skeletal muscle.

Twitch tension and maximal unloaded velocity of human knee extensor muscles were studied under conditions of low phosphate content of the phosphorylatable light chains (P-light chains) of myosin and elevated phosphate content, following a 10-s maximal voluntary isometric contraction (MVC). After the MVC, twitch tension was significantly potentiated, with greater potentiation observed at a shorter muscle length (p less than 0.05). The MVC was associated with at least a twofold increase in phosphate content of the fast (LC2F) and two slow (LC2S and LC2S') P-light chains, but this increase was unrelated to muscle length. No significant differences in knee extension velocity were observed between conditions where P-light chains had low or elevated phosphate content. Positive but nonsignificant correlations were noted between the extent of twitch potentiation and phosphate content of individual P-light chains as well as the percentage of type II muscle fibres in vastus lateralis muscle. No significant relationships were determined for myosin light chain kinase activity and either P-light chain phosphorylation or type II fibre percentage. These data suggest that, unlike other mammalian fast muscles, P-light chain phosphorylation of mixed human muscles is not strongly associated with altered contractile performance.

Adolescent↗

PubMed1988

Splenic immune responses following treadmill exercise in mice.

The in vitro proliferation response to lipopolysaccharide and pokeweek mitogen by splenic lymphocytes and the effect on the total splenic lymphocyte number were examined in C57BL/6J mice following an 8-week treadmill training program (30 m/min, 8 degrees slope, 30 min/day, 5 times/week) and after a single bout of exhaustive exercise (50% stepwise increases in final running speed for 10-min intervals). Plasma corticosterone levels were also measured to evaluate whether changes in adrenocortical activation were associated with exercise-induced immunomodulation. In comparison to sedentary controls, trained mice had an increase of 35% in succinate dehydrogenase activity per unit of protein in the quadriceps femoris muscle. Trained mice showed an increase in splenic lymphocyte proliferation to both mitogens which was evident 72 h after completion of the final training session, relative to sedentary controls. Immediately following exercise, however, lymphocyte proliferative responses were depressed compared with the training and the control values. The exercise regimen resulted in a reduction in total number of mononuclear cells per spleen. Changes in plasma corticosterone levels after exercise were not clearly associated with immunodepression or immunoenhancement of splenic lymphocyte mitogenesis. Taken together, the data suggest that moderate endurance training augments splenic B lymphocyte mitogenesis and further, that the immediate effects of exercise on splenic immune function vary with the duration and intensity of the work.

Animals↗

PubMed1987

Myosin light chain phosphorylation in intact human muscle.

The phosphate content of the fast (LC2F) and two slow (LC2S and LC2S1) phosphorylatable light chains (P-light chains) in myosin isolated from biopsy samples of rested human vastus lateralis muscle averaged 0.21, 0.28 and 0.25 mol of phosphate per mol of P-light chain, respectively. Following a 10 s maximal contraction, phosphate content was increased by almost 2-fold in the fast and two slow P-light chains. After prolonged, moderate cycling activity phosphate content was only slightly increased in the three P-light chains. These data suggest that, unlike animal skeletal muscle, myosin light chain kinase and phosphatase activities are similar in human fast and slow muscle fibres.

Biopsy, Needle↗

PubMed1987

Performance during the Wingate anaerobic test and muscle morphology in males and females.

Performance indices during the Wingate 30-s anaerobic test and their relationship to muscle morphology of the vastus lateralis muscle were studied in 30 untrained male and female subjects. Absolute values for peak power (P05), total work performed (TW), power decrease (PD), and post-test blood lactate concentration were significantly greater for the male subjects. When expressed per unit of body mass or leg volume, both P05 and TW were larger for the males than the females (P less than 0.05). Significant correlations were noted for P05, TW, PD, and blood lactate and the percent of fast-twitch (FT) fibers and the percent relative area of FT fibers for the male but not the female subjects. The results from this experiment reveal a significant influence of muscle morphology on short-term anaerobic work performance for these male subjects. The absence of a similar relationship for the women subjects was likely due to the use of an inappropriately high resistance setting.

Adult↗

PubMed1987

Supramaximal exercise after training-induced hypervolemia. II. Blood/muscle substrates and metabolites.

Blood and muscle substrates and metabolites were investigated in six healthy males (ranging in age from 19 to 23 yr) during three consecutive days of supramaximal exercise training. Muscle biopsies from the vastus lateralis and arterialized blood samples from a hand vein were extracted before the exercise and at selected times during the intermittent (1 min work to 4 min rest) cycling. The results indicated that blood glucose concentration was significantly depressed (P less than 0.05) on both days 2 and 3 of the training, whereas plasma free fatty acids and blood glycerol, pyruvate, alanine, and lactate were unaffected. At the muscle level, glucose and lactate concentrations were depressed on days 2 and 3, whereas ATP and glycogen were reduced only on the final day of training. No training-induced alterations were noted for muscle glucose 6-phosphate or muscle ADP. These results indicate that the approximate 10-11% reduction in O2-carrying capacity accompanying the short-term training does not directly and negatively influence muscle energy metabolism during the exercise. Rather, the explanation for the altered muscle and blood constituents must be sought from other effects of the training such as impaired carbohydrate repletion.

Adenosine Triphosphate↗

PubMed1986

Decrease in myosin light chain kinase activity of rabbit fast muscle by chronic stimulation.

Analysis of myosin light chain kinase (MLCK) activity in tibialis anterior muscles of the rabbit revealed that chronic stimulation at a frequency of 10 Hz for 24 h per day reduced the enzyme activity in a time-dependent manner. Since fast twitch muscle contains significantly more myosin light chain kinase than slow twitch muscle, the observed reductions are consistent with the type of fast-to-slow transformation observed for other type-specific muscle characteristics. The present data also indicate that the stimulation-induced decrease in MLCK activity precedes the fast-to-slow conversion of the myosin molecule as judged by pyrophosphate-polyacrylamide gel electrophoresis.

Animals↗

PubMed1986

Chronic exercise stress in mice depresses splenic T lymphocyte mitogenesis in vitro.

This study investigated changes in functional response to splenic T lymphocytes of mitogens following acute and chronic exposure to endurance exercise. Splenic T cell response in vitro to concanavalin A (Con A) and the total number of lymphocytes per spleen were compared between mice assigned to the following treatment conditions: (a) exercise training (EX) by treadmill running (28 m/min, 8 degrees slope for 30 min, 5 times per week for 4 weeks preceded by 2 weeks of endurance build-up), (b) exercise training as above followed by a single, acute bout of exercise to exhaustion (EX + AC) (35 m/min, 8 degrees slope, 30 min to 2 h duration) (c) exposure to the novel environment for 6 weeks without exercise (control), and exposure to the novel environment as in (c) followed by a single, acute bout of exercise to exhaustion. Treadmill running for 6 weeks significantly enhanced succinate dehydrogenase activity in skeletal muscle compared to the sedentary, control condition, and was broadly interpreted as indicative of a training effect. EX mice had significantly reduced splenic lymphocyte proliferative responses to optimal and supraoptimal concentrations of Con A compared with control animals. Incorporation of [3H]thymidine into splenic lymphocytes from EX + AC mice was the most markedly depressed. Total number of lymphocytes per spleen was significantly lower in EX compared with control mice. These results suggests that chronic exercise challenge in mice is associated with T lymphocyte hyporesponsiveness in the secondary lymphoid organs, such as the spleen.

Animals↗

PubMed1985

Phosphorylation of rabbit skeletal muscle myosin in situ.

Myosin light chain (P light chain) is phosphorylated by Ca2+ X calmodulin-dependent myosin light chain kinase. Based on studies with rat skeletal muscles, it has been shown that P light chain phosphorylation correlated to the extent of potentiation of isometric twitch tension. It is not clear whether this correlation exists in rabbit skeletal muscle, which has been the primary source of contractile proteins for biochemical studies. Therefore, phosphorylation of myosin P light chain in rabbit slow-twitch soleus and fast-twitch plantaris muscles in situ was examined. Electrical stimulation (5 Hz, 20 seconds) of plantaris muscle produced an increase in the phosphate content of P light chain from 0.17 to 0.45 mol phosphate/mol P light chain. This increase in phosphate content was accompanied by a 58% increase in maximal isometric twitch tension. Tetanic stimulation (100 Hz, 15 seconds) of rabbit soleus muscle resulted in only a small increase in P light chain phosphate content from 0.02 to 0.10 mol phosphate/mol P light chain, and posttetanic twitch tension did not increase significantly. The correlation between potentiated isometric twitch tension and P light chain phosphorylation in rabbit fast-twitch muscle is similar to that observed in rat skeletal muscle. These results were consistent with the hypothesis that phosphorylation of rabbit skeletal muscle myosin, which results in an increase in actin-activated ATPase activity, may be related to isometric twitch potentiation.

Animals↗

PubMed1985

Myosin light chain phosphorylation and isometric twitch potentiation in intact human muscle.

The effects of a single voluntary contraction of the quadriceps muscle group on phosphate incorporation into the phosphorylatable light chains (P-light chains) of fast and slow myosin isolated from the vastus lateralis muscle and potentiation of the electrically stimulated twitch tension was studied in intact human muscle. Twitch potentiation was maximal 20 s after the voluntary contraction. Thereafter, twitch potentiation declined, but was still significantly higher than pre-contraction values 2 min after the voluntary contraction. Phosphate incorporation into the P-light chain of fast myosin followed a similar time course to twitch potentiation, but no phosphate was incorporated into slow myosin P-light chains. These observations suggest that myosin light chain kinase activity is mainly associated with fast-twitch muscle fibers and, in agreement with previous studies, suggests that twitch potentiation associated with P-light chain phosphorylation is confined to the fast-twitch fibers of human muscle.

Adult↗

PubMed1985

Torque-velocity characteristics and muscle fiber type in human vastus lateralis.

The relationship between torque-velocity characteristics of the knee extensors during isokinetic contractions and muscle fiber type of the vastus lateralis, determined from two muscle biopsy samples, was investigated in 12 male and 18 female subjects. Peak torque, corrected for the effect of gravity and impact artifact, was classified as corrected peak torque. The torque measured 30 degrees from full extension and, corrected for gravity, was classified as corrected torque at 30 degrees. No significant correlations were found between the percentage of fast-twitch fibers (%FT) or the relative area of FT fibers (%FTA) and corrected peak torque values for any of the velocities tested or the knee angles where corrected peak torques were measured. However, significant inverse relationships were determined for corrected torque at 30 degrees at all but the fastest velocity (270 degrees/s) and both %FT and %FTA for the male subjects. These results reveal that muscle fiber type of the vastus lateralis, based on duplicate muscle samples, is not related to the peak torque actually generated by the knee extensors but may influence the shape of the torque output for maximal contractions sustained over the entire range of motion.

Adult↗

PubMed1984

Effects of concentric and eccentric exercise on protein catabolism in man.

To test the effects of different modes of exercise on indices of protein catabolism, eight adult males on a meat-free diet performed single 60-min bouts of concentric and eccentric cycle ergometer exercise in two 7-day periods. Although the absolute intensities for the two exercise bouts were similar, VO2 averaged 70% and 40% of VO2 max for the concentric and eccentric exercise, respectively. Mean heart rate during the eccentric exercise was 26% lower (P less than 0.001) than during concentric exercise, and only for the latter was post-exercise lactate significantly elevated. The excretion of 3-methylhistidine, creatinine, and urea in 24 h urine samples was constant over the 2 weeks in which exercise was performed. Compared to pre-exercise values, the concentrations of 3-methylhistidine, creatinine, and urea were unchanged in serum samples obtained immediately after and for up to 48 h following eccentric exercise. However, serum urea concentration was elevated by 18% and 21% (P less than 0.05) in samples obtained immediately and 1 h after concentric exercise only. Despite the fact that the eccentric exercise was associated with delayed muscle soreness, these results reveal that neither concentric nor eccentric cycling exercise at moderate intensity had a major influence on indices of protein catabolism.

Adult↗

PubMed1984

Fiber type distribution and maximal activities of enzymes involved in energy metabolism following short-term supramaximal exercise.

Alterations in enzyme activities involved in muscle energy metabolism and the muscle fiber type distribution were investigated in six subjects, ranging in age from 19-23 years, following short-term, high intensity exercise. Changes in the vastus lateralis muscle were studied prior to exercise and approximately 24 h after each of 2 consecutive days of supramaximal cycling exercise (120% VO2 max) performed intermittently as 1-min work to 4-min rest until fatigue or until 24 repetitions had been completed. The results indicated that there were no changes (P greater than 0.05) in maximal in vitro activities for representative enzymes of beta-oxidation (3-hydroxyacyl CoA dehydrogenase, HAD), the citric acid cycle (succinic dehydrogenase, SDH), glucose phosphorylation (hexokinase, HK), glycogenolysis (total phosphorylase, PHOSPH), or glycolysis (phosphofructokinase, PFK; pyruvate kinase, PK; lactate dehydrogenase, LDH) in spite of the large increase in carbohydrate utilization and glycolytic flux rate. In addition, although no change in fiber type distribution was found in the pre-exercise biopsy between days, an acute reduction (P less than 0.05) in type I fiber distribution occurred with exercise. It is concluded that supramaximal exercise performed on a short-term basis does not alter the enzymatic profile or the fiber type distribution when measured 24 h following the activity.

Adult↗

PubMed1984

Alterations in blood volume following short-term supramaximal exercise.

To investigate the role of high-intensity intermittent exercise on adaptations in blood volume and selected hematological measures, four male subjects aged 19-23 yr [peak O2 consumption (VO2max) = 53 ml X min-1 X kg-1] performed supramaximal (120% VO2max) cycle exercise on 3 consecutive days. Each exercise session consisted of intermittent work performed as bouts of 1-min work to 4-min rest until fatigue or until a maximum of 24 repetitions had been completed. Measurements on blood samples were made before the exercise period and 24 h after the last exercise session. Plasma volume (PV) estimated using 131I-human serum albumin increased by 11.6% (3,504 vs. 3,912 ml; P less than 0.05). Total blood volume (TBV) based on PV and hematocrit (Hct) values increased by 4.5% (5,798 vs. 6,059 ml; P less than 0.05), whereas red cell volume (RCV) decreased by 6.4% (2,294 vs. 2,147 ml; P less than 0.05). Measurements of hematological indices indicated significant reductions (P less than 0.05) in whole-blood Hct (39.7 vs. 35.5%), hemoglobin concentration (15.5 vs. 13.9 g/100 ml), hemoglobin content (897 vs. 839 g), and red blood cell count (5.15 vs. 4.55 X 10(6) X mm-3). The findings of this study suggest that exercise intensity is a major factor in promoting exercise-induced hypervolemia and that rapid elevations in PV can be induced early in training.

Adult↗

PubMed1984

Exercise and protein catabolism in women.

To test the effects of exercise on indices of protein metabolism, 8 sedentary, young women performed single bouts of prolonged submaximal and intermittent supramaximal exercise. The excretion of 3-methylhistidine, urea and creatinine in 24-hour urine samples was constant over the 11-day experimental period, although the plasma urea concentration was elevated in blood samples obtained immediately after and 6 h following the prolonged exercise only. The results suggest that the acute exercise described here has a minimal effect on protein metabolism, and does not lead to a noticeable change in myofibrillar protein degradation in young women.

Adult↗