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R K Josephson

Publications and source records attributed to R K Josephson.

At least 19 recordsLinked to original sources
PubMed2001

The efficiency of an asynchronous flight muscle from a beetle.

Mechanical power output and metabolic power input were measured from an asynchronous flight muscle, the basalar muscle of the beetle Cotinus mutabilis. Mechanical power output was determined using the work loop technique and metabolic power input by monitoring CO(2) production or both CO(2) production and O(2) consumption. At 35 degrees C, and with conditions that maximized power output (60 Hz sinusoidal strain, optimal muscle length and strain amplitude, 60 Hz stimulation frequency), the peak mechanical power output during a 10 s burst was approximately 140 W kg(-1), the respiratory coefficient 0.83 and the muscle efficiency 14-16 %. The stimulus intensity used was the minimal required to achieve a maximal isometric tetanus. Increasing or decreasing the stimulus intensity from this level changed mechanical power output but not efficiency, indicating that the efficiency measurements were not contaminated by excitation of muscles adjacent to that from which the mechanical recordings were made. The CO(2) produced during an isometric tetanus was approximately half that during a bout of similar stimulation but with imposed sinusoidal strain and work output, suggesting that up to 50 % of the energy input may go to muscle activation costs. Reducing the stimulus frequency to 30 Hz from its usual value of 60 Hz reduced mechanical power output but had no significant effect on efficiency. Increasing the frequency of the sinusoidal strain from 60 to 90 Hz reduced power output but not CO(2) consumption; hence, there was a decline in efficiency. The respiratory coefficient was the same for 10 s and 30 s bursts of activity, suggesting that there was no major change in the fuel used over this time range. The mass-specific mechanical power output and the efficiency of the beetle muscle were each 2-3 times greater than values measured in previous studies, using similar techniques, from locust flight muscles, which are synchronous muscles. These results support the hypothesis that asynchronous flight muscles have evolved in several major insect taxa because they can provide greater power output and are more efficient than are synchronous muscles for operation at the high frequencies of insect flight.

Animals↗
PubMed2000

Power output by an asynchronous flight muscle from a beetle.

The basalar muscle of the beetle Cotinus mutabilis is a large, fibrillar flight muscle composed of approximately 90 fibers. The paired basalars together make up approximately one-third of the mass of the power muscles of flight. Changes in twitch force with changing stimulus intensity indicated that a basalar muscle is innervated by at least five excitatory axons and at least one inhibitory axon. The muscle is an asynchronous muscle; during normal oscillatory operation there is not a 1:1 relationship between muscle action potentials and contractions. During tethered flight, the wing-stroke frequency was approximately 80 Hz, and the action potential frequency in individual motor units was approximately 20 Hz. As in other asynchronous muscles that have been examined, the basalar is characterized by high passive tension, low tetanic force and long twitch duration. Mechanical power output from the basalar muscle during imposed, sinusoidal strain was measured by the work-loop technique. Work output varied with strain amplitude, strain frequency, the muscle length upon which the strain was superimposed, muscle temperature and stimulation frequency. When other variables were at optimal values, the optimal strain for work per cycle was approximately 5%, the optimal frequency for work per cycle approximately 50 Hz and the optimal frequency for mechanical power output 60-80 Hz. Optimal strain decreased with increasing cycle frequency and increased with muscle temperature. The curve relating work output and strain was narrow. At frequencies approximating those of flight, the width of the work versus strain curve, measured at half-maximal work, was 5% of the resting muscle length. The optimal muscle length for work output was shorter than that at which twitch and tetanic tension were maximal. Optimal muscle length decreased with increasing strain. The curve relating work output and muscle length, like that for work versus strain, was narrow, with a half-width of approximately 3 % at the normal flight frequency. Increasing the frequency with which the muscle was stimulated increased power output up to a plateau, reached at approximately 100 Hz stimulation frequency (at 35 degrees C). The low lift generated by animals during tethered flight is consistent with the low frequency of muscle action potentials in motor units of the wing muscles. The optimal oscillatory frequency for work per cycle increased with muscle temperature over the temperature range tested (25-40 degrees C). When cycle frequency was held constant, the work per cycle rose to an optimum with increasing temperature and then declined. We propose that there is a temperature optimum for work output because increasing temperature increases the shortening velocity of the muscle, which increases the rate of positive work output during shortening, but also decreases the durations of the stretch activation and shortening deactivation that underlie positive work output, the effect of temperature on shortening velocity being dominant at lower temperatures and the effect of temperature on the time course of activation and deactivation being dominant at higher temperatures. The average wing-stroke frequency during free flight was 94 Hz, and the thoracic temperature was 35 degrees C. The mechanical power output at the measured values of wing-stroke frequency and thoracic temperature during flight, and at optimal muscle length and strain, averaged 127 W kg(-1)muscle, with a maximum value of 200 W kg(-1). The power output from this asynchronous flight muscle was approximately twice that measured with similar techniques from synchronous flight muscle of insects, supporting the hypothesis that asynchronous operation has been favored by evolution in flight systems of different insect groups because it allows greater power output at the high contraction frequencies of flight.

Animals↗
PubMed2000

Asynchronous muscle: a primer.

The asynchronous muscles of insects are characterized by asynchrony between muscle electrical and mechanical activity, a fibrillar organization with poorly developed sarcoplasmic reticulum, a slow time course of isometric contraction, low isometric force, high passive stiffness and delayed stretch activation and shortening deactivation. These properties are illustrated by comparing an asynchronous muscle, the basalar flight muscle of the beetle Cotinus mutabilis, with synchronous wing muscles from the locust, Schistocerca americana. Because of delayed stretch activation and shortening deactivation, a tetanically stimulated beetle muscle can do work when subjected to repetitive lengthening and shortening. The synchronous locust muscle, subjected to similar stimulation and length change, absorbs rather than produces work.

Animals↗
PubMed1999

Dissecting muscle power output.

The primary determinants of muscle force throughout a shortening-lengthening cycle, and therefore of the net work done during the cycle, are (1) the shortening or lengthening velocity of the muscle and the force-velocity relationship for the muscle, (2) muscle length and the length-tension relationship for the muscle, and (3) the pattern of stimulation and the time course of muscle activation following stimulation. In addition to these primary factors, there are what are termed secondary determinants of force and work output, which arise from interactions between the primary determinants. The secondary determinants are length-dependent changes in the kinetics of muscle activation, and shortening deactivation, the extent of which depends on the work that has been done during the preceding shortening. The primary and secondary determinants of muscle force and work are illustrated with examples drawn from studies of crustacean muscles.

Animals↗
PubMed1998

Changes in the maximum speed of shortening of frog muscle fibres early in a tetanic contraction and during relaxation.

1. Isotonic shortening velocities at very light loads were examined in single fibres of the anterior tibialis muscle of the frog, Rana temporaria, using load-clamp recording and slack tests (temperature, 1-3 degrees C; initial sarcomere length, 2.25 microns). 2. Shortening velocities at very light loads (force-clamp recording) were found to be higher early in the rise of a tetanic contraction than during the plateau of the contraction. The upper limit of the load at which there was elevated shortening velocity early in the contraction was 1.5-5.4% of the maximum tetanic tension (Fo) depending on the particular fibre. 3. The maximum shortening velocity determined using the slack test method (Vo) was as much as 30% greater early in a contraction than at the tetanic plateau. Vo was elevated above the plateau level up to about 30 ms after the end of the latent period, which is equivalent to the time required for the force in an isometric contraction to rise to about 30% of Fo. Vo is depressed below the plateau value during relaxation at the cessation of stimulation. 4. Stimulation studies show that the cross-bridge model of Huxley (1957) predicts the maximum shortening velocity to be greater early in a contraction, when new actin binding sites are becoming activated and new cross-bridge connections are being formed rapidly, than during steady-state contraction. The elevated shortening velocity in the model is a consequence of new cross-bridges being formed in the pulling configuration, and there being a delay before the newly added bridges are dragged beyond their equilibrium position so they begin to retard shortening. The model also predicts that maximum shortening velocity should be depressed below the plateau level during early relaxation as cross-bridge binding sites are rapidly removed from the active population.

Algorithms↗
PubMed1995

Influence of muscle length on work from trabecular muscle of frog atrium and ventricle.

The work capacity of segments of atrial and ventricular muscle from the frog Rana pipiens was measured as a function of muscle length using the work loop technique. Both the work done during shortening and the work required to re-lengthen the muscle after shortening increased with muscle length. Net work increased with length up to a maximum, beyond which work declined. The optimum sarcomere length for work output was 2.5-2.6 microns for both atrial and ventricular muscle. Isometric force increased with muscle length to lengths well beyond the optimum for work output. Thus, the decline in work at long lengths is not simply a consequence of a reduction in the capacity of heart muscle to generate force. It is proposed that it is the non-linear increase in work required to re-lengthen muscle with increasing muscle length which limits net work output and leads to a maximum in the relationship between net work and muscle length. Extension of the results from muscle strips to intact hearts suggests that the work required to fill the ventricle exceeds that available from atrial muscle at all but rather short ventricular muscle lengths.

Animals↗
PubMed1992

Structural organization of two fast, rhythmically active crustacean muscles.

The organization of the flagellum abductor muscle and of a scaphognathite levator muscle of the green crab, Carcinus maenas, has been compared quantitatively using light and electron microscopy. These muscles are rhythmically active at relatively high frequencies and for long durations. Fibers of both muscles are interconnected to form fascicles of 50 or more fibers within which there is cytoplasmic continuity. A single muscle is made up of 8-12 fascicles. Individual fibers consist of a peripheral rind of densely packed mitochondria, a thick region of glycogen granules, and myofibrils arranged into scattered central islands. Less than half the volume-density of these muscles is contractile material, the balance being largely mitochondria and glycogen. The fibers within a muscle are structurally similar. They have short sarcomeres (about 2 microns), thin to thick filament ratios of about 3:1, and junctions between the sarcoplasmic reticulum and the transverse tubules at the M line. Sarcoplasmic reticulum occupies about 10% of the myofibrillar volume-density. A well developed sarcoplasmic reticulum appears to underlie the capacities of these two muscles for high frequency contraction; extensive mitochondria and glycogen stores should confer fatigue resistance under both aerobic and anaerobic conditions.

Animals↗
PubMed1991

The efficiency of a flight muscle from the locust Schistocerca americana.

1. The efficiency of the metathoracic tergosternal muscle of the locust Schistocerca americana was examined by simultaneously measuring work output from the muscle and oxygen consumption by the muscle. The work output was determined using the work-loop technique in which the muscle is subjected to periodic strain and to phasic stimulation in the strain cycle. The area of the loop formed by plotting muscle force against muscle length over a cycle is the net work output for that cycle. 2. The tergosternal muscle is a synchronous, parallel-fibred muscle containing two motor units with similar contraction kinetics. The average twitch rise time (30 degrees C) was 15 ms, the twitch duration (to 50% relaxation) was 26 ms, and the peak twitch tension with both units active was 73 kN m-2. The maximum mechanical power output during sinusoidal shortening at 20 Hz with both motor units active and stimulated once per cycle averaged 37 W kg-1. 3. The overall efficiency of the tergosternal muscle averaged 6.4% (range 4-10%) where efficiency is defined as the ratio of the net work done (20 Hz sinusoidal strain, 1 stimulus per cycle, optimum strain amplitude and stimulus phase) to the caloric equivalent of the oxygen consumed. The efficiency was independent of the duration of the test period (examined range = 10-30 s) and the same when both motor units were active as when only one was stimulated. 4. Stimulating the muscle with two stimuli per cycle (interstimulus interval = 6 ms) increased the work per cycle by about 13% above that with single stimuli per cycle, but the muscle fatigued more rapidly and after 15-25 s the power output was less with two stimuli per cycle than with one. The efficiency with two stimuli per cycle was slightly less than that with one shock per cycle. 5. The oxygen consumption during normal work cycles at 20 Hz with optimum stimulus phase and strain was greater by about 15% than the oxygen consumption during isometric contractions at the same frequency.

Animals↗
PubMed1988

The consequences of fibre heterogeneity on the force-velocity relation of skeletal muscle.

The consequences of fibre heterogeneity on the collective force-velocity properties of bundles of parallel fibres were examined in a simulation model. The model was tested by comparing the actual force-velocity curve of a bundle of three fibres, each of which had been individually characterized, with the force-velocity curve predicted by the model for the bundle based on the individual fibre properties. The predicted and measured force-velocity curves were in excellent agreement. The curvature of the force-velocity relation for a muscle, as indicated by a/P0 in Hill's (1938) hyperbolic equation, increases with increasing heterogeneity in the maximum shortening velocities (Vmax(i] of the individual fibres in the muscle. In a muscle that is heterogeneous with respect to Vmax(i), the maximum shortening velocity determined by the slack test method (V0) can be expected to represent the fastest fibre(s) in the muscle. The maximum velocity of shortening (Vm), determined by extrapolation from a hyperbola that is fitted to force-velocity data at finite loads, is substantially lower than V0. The difference in estimates of V0 and Vm is a function of: (i) the degree of heterogeneity of the muscle with respect to Vmax(i) and the curvature of the force-velocity relationship of the individual fibres, and (ii) the force range used to establish the hyperbola from which Vm is derived. The ratio of Vm to V0 can be used as an index to estimate the degree of variability in the maximum velocity of shortening among individual fibres in a muscle.

Animals↗
PubMed1987

Innervation is necessary for the development of fast contraction kinetics of singing muscles in a katydid.

The twitch duration of mesothoracic wing muscles of the male katydid Neoconocephalus robustus (Insecta; Orthoptera; Tettigoniidae) decreases rapidly within the first 5 days of adulthood, to about half of its value in newly molted adults. To determine if this change is dependent upon neural input, male mesothoracic first tergocoxal muscles were unilaterally denervated on the second day of adulthood. The contraction kinetics of the denervated and contralateral innervated muscles were tested four days later. The development of rapid contraction kinetics was slowed or stopped in the denervated muscles, while the contralateral innervated muscles did become faster. Mesothoracic wing muscles of females do not develop faster contraction kinetics. When the female mesothoracic first tergocoxal muscle is denervated, there is no difference in twitch duration after 4 days between the innervated and contralateral denervated muscles. Therefore, denervation in newly molted adult male katydids interrupts a developmental program for the acquisition of adult contraction kinetics.

Animals↗
PubMed1983

Cobalt uptake and localization of putative calcium binding sites in striated muscle.

Frog sartorius muscles were soaked overnight in saline containing 50 mM cobalt and subsequently fixed with or without precipitation of intracellular cobalt by exposure to ammonium sulfide. Treated fibers and appropriate controls were embedded in plastic in the usual manner. Thick sections (3-4 micrometers) of each sample were treated with silver in order to intensify precipitated cobalt. The samples were then resectioned for ultrastructural examination. Fibers exposed to cobalt with or without precipitation had normal ultrastructure; indeed, the transverse lines of the A-zone and M-band appeared to be more obvious after exposure to cobalt than in control samples. Exposure to silver produced numerous silver grains only in those samples that contained precipitated cobalt. The distribution of silver grains after intensification matched expected calcium binding sites. Silver grains were abundant over membranes of the sarcoplasmic reticulum, sarcolemma, mitochondria, and nucleus and rare or absent from filaments and sarcoplasm. This technique appears to be generally useful for locating intracellular calcium binding sites.

Animals↗
PubMed1982

Lability of conduction velocity during repetitive activation of an excitable epithelium.

Conduction velocity lability was studied in the electrically excitable epithelium of Euphysa japonica by means of intracellular recordings. Three classes of response latency change were identified in response to bursts of stimuli: an initial jump, uniform drift and abrupt jumps in latency. In each case an increase in stimulus frequency produced an increase in latency. The initial jump in latency, which occurred between the first and second response of a series, was related to the afterpotential of the first response. The increased latency of the second response appears to result from the drop in membrane resistance during the hyperpolarizing afterpotential. The uniform drift in latency remains unexplained but may be the result of ion accumulation within the tissue, progressive inactivation of the ionic channels involved in producing the action potential, or junctional phenomena. The abrupt jumps in latency, which often preceded failure to respond, were found to be impulse initiation phenomena.

Action Potentials↗
PubMed1981

Collateral sprouting of insect motorneurons.

The metathoracic extensor tibiae muscle of the cricket, Teleogryllus oceanicus, is innervated by two excitatory axons: a fast axon, which initiates large twitches to single stimuli, and a slow axon, which evokes minute twitches to single stimuli, but which, through facilitation and summation, evokes readily measurable tension to repetitive stimulation. The fast axon and the slow axon leave the metathoracic ganglia in different nerve roots, the fast axon through nerve 5 and the slow axon through nerve 3. The fast axon innervates muscle fibers in the middle of the extensor tibiae, and the slow axon innervates muscle fibers at the proximal and distal ends of the muscle. A central region of muscle fibers is innervated by only the fast axon. This region is flanked on either side by dually innervated fibers, fibers that receive both the fast and the slow axons. Fibers with only slow axon innervation are restricted to a wedge-shaped patch in the proximal extensor tibiae and a larger region in the most distal portion of the muscle. Sectioning nerve 5 containing the fast axon, or nerve 3 containing the slow axon, partially denervates the extensor tibiae. Functional transmission by the fast axon fails 7-10 days after nerve section. The innervation field of the intact motorneuron expands in a partially denervated muscle. The linear expansion rate of the slow axon field is about 20-40 micrometer per day. The enlarged slow field does not regress when axons regenerate to the muscle through nerve 5. The progressive expansion of the slow innervation field suggests that the expansion is due to collateral sprouting of slow axon terminals.

Animals↗
PubMed1981

Increased effectiveness of a motorneuron after partial denervation of its target muscle in the cricket Telegryllus oceanicus.

Fibers of the metathoracic extensor tibia muscle of the cricket Teleogryllus oceanicus are innervated by a slow excitatory axon (slow fibers), a fast excitatory axon (fast fibers), or by both slow and fast axons (dual fibers). Sectioning metathoracic nerve 5 removes the fast axon input to the muscle but not that of the slow axon. Following such partial denervation, the mechanical responses initiated by the slow axon increase progressively for at least 30 days; twitch tensions reach 5-10 times those of control muscles and tetanic tensions 10-30 times control values. After sectioning nerve 5, resting membrane potentials decrease in those fibers which originally received fast axon input and the input resistance of all fiber types increases, including that of slow fibers which are not innervated through nerve 5. Excitatory junctional potentials (EJPs) initiated by the slow axon become larger following partial denervation, accounting in part for the larger contraction amplitudes. The increased input resistance is adequate to account for the larger EJPs in slow fibers but not for the proportionally greater increase in EJP amplitude in fibers which were formerly dually innervated. The change in EJP amplitude is abrupt in slow fibers and gradual in formerly dual fibers.

Animals↗
PubMed1979

Electrical properties of an excitable epithelium.

The exumbrellar epithelium of the hydromedusa, Euphysa japonica, is composed of a single layer of broad (70 micrometers), thin (1--2 micrometers) cells which are joined by gap junctions and simple appositions. Although the epithelium lacks nerves, it is excitable; electrically stimulating the epithelium initiates a propagated action potential. The average resting potential of the epithelial cells is -46 mV. The action potential, recorded with an intracellular electrode, is an all-or-nothing, positive, overshooting spike. The epithelial cells are electrically coupled. The passive electrical properties of the epithelium were determined from the decrement in membrane hyperpolarization with distance from an intracellular, positive current source. The two-dimensional space constant of the epithelium is 1.3 mm, the internal longitudinal resistivity of the cytoplasm and intercellular junctions is 196 omega cm, and the resistivity of both apical and basal cell membranes is greater than 23 k omega cm2. Although the membrane resistivity is high, the transverse resistivity of the epithelium is quite low (7.5 omega cm2), indicating that the epithelium is leaky with a large, transverse, paracellular shunt.

Action Potentials↗
PubMed1978

Peripheral control of responsiveness to auditory stimuli in giant fibres of crickets and cockroaches.

Auditory stimuli initiate ascending activity in large fibres of the ventral nerve cord of the cricket, Acheta domesticus, and the cockroach, Periplaneta americana. This auditory responsiveness is reduced during locomotion. An earlier study concluded that the depression of responsiveness was mediated by descending inhibition. However, the auditory responsiveness is reduced during locomotion even after section of the ventral nerve cord anterior to the abdominal recording electrodes. Further, auditory responsiveness of isolated abdomens attached to intact animals is inhibited during locomotion of their hosts. Laminar wind streams over the cerci depress responsiveness to sound, but only at velocities markedly higher than those encountered by freely walking animals. Although the exact mechanism is not known, the depressed auditory responsiveness can occur independently of any descending influences.

Acoustic Stimulation↗