A diffractometer using a lateral effect photodiode for the rapid determination of sarcomere length changes in cross-striated muscle

A simple method is devised to record rapid sarcomere length changes of muscle fibres using a lateral effect diode. In the standard position the diffractometer records length changes between 1.65 and 3.8 m, the output being linear 1 V/m with a frequency response of –3 dB at 1.2 kHz. The absolute error is<0.05 m between 1.65 and 2.80 m and <0.1 m between 2.81 and 3.30 m. The resolution of length changes is<0.005 m over the whole range. By varying the detector position the length range can be extended to either side, and spatial resolution can be improved at the expense of length range.     

Potassium induced potential changes in rat diaphragm muscle

Summary The effect of different potassium concentrations on the membrane potential and membrane resistance of rat diaphragm muscle fibres was measured by means of a double sucrose gap method and a microelectrode technique. Concentration measurements showed that the muscle fibres gained sodium and lost potassium in the equilibration period.In the absence of external chloride changing the external potassium concentration from 2.8 mM to potassium-free caused a depolarization of the membrane of about 30 mV and a small increase in membrane resistance.This K-dependent potential change (K-response) was reduced by ouabain, K-strophanthin, 2,4-dinitrophenol and cyanide, indicating that an energy requiring process is involved. The temperature dependence of the K-response found is consistent with this assumption. Variation in potassium permeability in the absence and presence of external potassium could account for only 13% of the K-response.The K-response amplitude appeared to depend on the external potassium and the internal sodium concentration. Hyperpolarization of the membrane could not only be produced after readmission of potassium but also after addition of thallium, the latter being more potent. Raising the external chloride concentration resulted in a decrease of the K-response and membrane resistance. The current, generating the Kresponse was shown to be hardly influenced by conditional polarization of the membrane.It is concluded from these results that the Kresponse is mainly due to the operation of an electrogenic sodium pump.     

Utilization of carbohydrates and free fatty acids by the gastrocnemius of the dog during long lasting rhythmical exercise

Summary Utilization of carbohydrates and free fatty acids (FFA) has been investigated in gastrocnemii of dogs during long lasting isotonic rhythmical exercise induced by supramaximal stimulation of the sciatic nerve. Uptake or output of gases and substrates was determined according to the Fick principle. The first measurements were done at about 2 min after the beginning of work when blood flow has reached a steady state, and the latest at about 100 min after the beginning of exercise.During the first 7 min when the work performed exceeded 5 kg/100g×min and O₂ consumption exceeded 11 ml/100g×min, uptake of arterial glucose and FFA was low, accounting for less than 40% of the total O₂ consumption. Since the RQ values at the same time were about 1.0, glycogen must have been oxidized as the major aerobic energy source.About 13 min after the beginning of exercise, the work the muscles could perform declined to about half of the initial value and remained so for the following 90 min. During this time the oxygen extraction ratio of FFA was about 50% and of arterial glucose was 40–50%, while the RQ value was about 0.8.During initial strong exercise an output of lactic acid (LA) of about 10 mg/100 g×min was measured. With the decrease of work as a consequence of fatigue, LA output became negligible, and in many experiments small amounts of LA were taken up by the working gastrocnemii.It is concluded that glycogen is the major aerobic energy source for strong muscular exercise which cannot be substituted for by the oxidation of arterial glucose or FFA.Supported by the Deutsche Forschungsgemeinschaft.     

Cross education of muscular strength during unilateral resistance training and detraining

Abstract. The purpose of the present study was to examine the changes in maximum voluntary isometric contraction (MVC) in the contralateral untrained limb during unilateral resistance training and detraining, and to examine the factors inducing these changes by means of electrophysiological techniques. Nine healthy males trained their plantar flexor muscles unilaterally 4 days·week^–1 for 6 weeks using 3 sets of 10–12 repetitions at 70–75% of one-repetition maximum a day, and detrained for 6 weeks. Progressive unilateral resistance training significantly (P<0.05) increased MVC, integrated electromyogram (iEMG), and voluntary activation in the trained and contralateral untrained limbs. The changes in MVC after training were significantly correlated with the changes in iEMG in both limbs. No significant changes occurred in MVC, voluntary activation, and iEMG in the contralateral limb after detraining. The changes in MVC after detraining did not correlate with the changes in voluntary activation or iEMG in either limb. Training and detraining did not alter twitch and tetanic peak torques in either limb. These results suggest that the mechanisms underlying cross education of muscular strength may be explained by central neural factors during training, but not solely so during detraining. Electronic Publication     

Role of cyclic nucleotides in regulation of pulmonary artery tone in rabbits

The involvement of cAMP- and cGMP-dependent signal systems into the regulation of the contractile reaction of smooth muscles of the rabbit pulmonary arteries was studied using a mechanographic method. For modulation of intracellular level of cyclic nucleotides we used adenylate cyclase activators -adrenoceptor agonist isadrin, guanylate cyclase inhibitor methylene blue, penetrating analog dibutyryl-cAMP, and phosphodiesterase inhibitors. The mechanisms of cAMP- and cGMP-dependent regulation of smooth muscle contractile activity were realized in close interrelationship, and the key component of this was cyclic nucleotide phosphodiesterases. The ratio of activities of phosphodiesterase subtypes in smooth-muscle cells can essentially modulate the adrenergic effects in the pulmonary artery wall and even invert them.     

Muscle fibre types in the suprahyoid muscles of the rat

Five muscle fibre types (I, IIc, IIa, IIx and IIb) were found in the suprahyoid muscles (mylohyoid, geniohyoid, and the anterior and posterior bellies of the digastric) of the rat using immuno and enzyme histochemical techniques. More than 90% of fibres in the muscles examined were fast contracting fibres (types IIa, IIx and IIb). The geniohyoid and the anterior belly of the digastric had the greatest number of IIb fibres, whilst the mylohyoid was almost exclusively formed by aerobic fibres. The posterior belly of the digastric contained a greater percentage of aerobic fibres (83.4%) than the anterior belly (67.8%). With the exception of the geniohyoid, the percentage of type I and IIc fibres, which have slow myosin heavy chain (MHCβ), was relatively high and greater than has been previously reported in the jaw‐closing muscles of the rat, such as the superficial masseter. The geniohyoid and mylohyoid exhibited a mosaic fibre type distribution, without any apparent regionalisation, although in the later MHCβ‐containing fibres (types I and IIc) were primarily located in the rostral 2/3 region. In contrast, the anterior and posterior bellies of the digastric revealed a clear regionalisation. In the anterior belly of the digastric 2 regions were observed: both a central region, which was almost exclusively formed by aerobic fibres and where all of the type I and IIc fibres were located, and a peripheral region, where type IIb fibres predominated. The posterior belly of the digastric showed a deep aerobic region which was greater in size and where type I and IIc fibres were confined, and a superficial region, where primarily type IIx and IIb fibres were observed.     

Inhibition versus facilitation of the reflex responsiveness of identified wrist extensor motor units by antagonist flexor afferent inputs in humans

The question of whether Ia reciprocal inhibition might depend on the motor task and on the type of motor unit activated was investigated in the human extensor carpi radialis muscles. Ia reciprocal inhibition induced by stimulating the median nerve (conditioning stimulation) was estimated by measuring the changes in the firing probability of 37 extensor motor units in response to the radial nerve stimulation (100 test stimuli) delivered 1 ms after the conditioning stimulation. Six subjects were asked to perform a task consisting of either selectively contracting their wrist extensor muscles or co-activating their wrist and finger antagonist muscles by clenching their hand around a manipulandum. In the control recordings (test stimulation alone), the mean response probability of the 37 motor units was found to be greater during hand clenching. The motor units were identified on the basis of their force thresholds, their macro-potentials, and their twitch contraction times. The data obtained in the control recordings were consistent with the size principle. In the recordings where the responses were conditioned by applying median nerve stimulation, the response probability of the motor units with low force thresholds, small macro-potential areas, and long twitch contraction times tended to decrease, in line with the presence of Ia reciprocal inhibition, whereas the response probability of the motor units with higher force thresholds, larger macro-potential areas, and shorter twitch contraction times tended to increase. The median nerve stimulation may therefore have altered the efficiency with which the extensor Ia inputs recruited the homonymous motoneurones in the pool. The flexor group I afferents activated while the median nerve was stimulated had inhibitory effects on the slow contracting motor units, and facilitatory effects mainly on the fast contracting motor units. Both of these effects were stronger during hand clenching, in which the numerous cutaneous receptors of the palm and fingertips are liable to be activated. Besides their own effects on the excitability of the various types of motor units, cutaneous inputs are known to potentiate the Ib interneurones. In addition, the effects of the conditioning stimulation were superimposed on the tonic activity of the Ia and Ib afferents from the flexor wrist and finger muscles. This may explain why both the inhibitory and facilitatory effects of the median nerve stimulation were enhanced during hand clenching.     

Favourable associations between the myosin heavy-chain and light-chain isoforms in human skeletal muscle

Histochemical and biochemical analyses were performed in order to examine the relationship between myosin light-chain (LC) isoforms and fibre-type distributions in whole human skeletal muscle. Muscle biopsies were obtained from the vastus lateralis muscle in six healthy men, and analysed for the relative area occupied by each fibre type (percentage of fibre type area) and the molar ratio of each LC isoform. The percentage of type I fibre area was positively correlated with the molar ratio of slow LC (LC1s and LC2s) to total LC. The regression line was located below the line of unity. Also, the ratio of percentage of type II fibre area to that of type II fibre area was positively correlated with the molar ratio of the fast alkali LC LC1f to fast alkali LCs LC1f and LC3f. These results support previous study, having shown that in human skeletal muscle some type I fibres express various amounts of fast LC in addition to slow LC and suggest that fast myosin heavy-chain HCII a is favourably associated with LC1f, whereas HCIIb is favourably associated with LC3f.     

Effect of an increased calcium ion concentration on electrical and contractile activity of the smooth muscles of the guinea pig ureter

Smooth muscle cells of the guinea pig ureter were studied by the double sucrose gap method. An increase in the calcium ion concentration in the Ringer-Locke solution to 22 mM led to hyperpolarization and to a slight increase in the resistance of the membrane. The amplitude of the first spike potential and the height of the plateau were lowered but the amplitude of the oscillations was increased. In sodium-free Ringer-Locke solution, when the action potential in the smooth muscle cells of the ureter was converted into a simple spike potential, a marked increase in amplitude of the action potential was observed with an increase in the calcium ion concentration.Department of Neuromuscular Physiology, A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. (Presented by Academician of the Academy of Medical Sciences of the USSR N. N. Gorev.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 5, pp. 522–526, May, 1977.     

Age changes in geometry and mineral content of the lower limb bones

Subperiosteal expansion and increase in second moments of area with aging of eleven femoral and tibial cross-sections are documented in a large archaeological sample from the American Southwest. In contrast to these geometric changes, we found little change with age in bone mineral density measured using photon absorptiometry. Thus, the most significant structural changes with age in bone appear to involve its geometry and material characteristics other than its density. Variation in age-related geometric remodeling between cross-section locations and populations may be caused by differences in mechanical stress and strain levels in vivo in the lower limb.