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Biomedical subjects

S R Taylor

Publications and source records attributed to S R Taylor.

At least 73 records · Page 4Linked to original sources
PubMed1983

Effect of surface texture on the soft tissue response to polymer implants.

The ion beam etching process produces micro hairlike filaments on PTFE without causing any chemical or physiochemical alterations to the material. Implantation of this textured material subcutaneously, altered the interfacial cells and the kinetics of fibrous capsule development. Interfacial cells associated with textured interfaces (shown to be monocytic phagocytes) display increases in adhesion, vacuolization, filopodia formation, cytoplasmic-to-nuclear ratio, metabolism, acid phosphatase activity, and increased FBGC formation. The fibrous capsule associated with textured implants is reduced in thickness at 8 weeks but is similar to smooth controls at later time periods. The results of this investigation demonstrate that the surface texture of an implant is a critical variable in determining the soft tissue response to a material.

Acid Phosphatase↗
PubMed1982

Cellular membrane potentials and contractile threshold in mammalian skeletal muscle susceptible to malignant hyperthermia.

An increase in external K+ can generate contractile force in muscle, and K+ contractures are an established means to determine the effect of an agent on the relation between membrane potential and mechanical activity [8]. We have used K+-contractures to further test our hypothesis [5] that abnormal cell membrane potential responses are intrinsic to skeletal muscle of Poland China pigs susceptible to malignant hyperthermia (MHS), and a nervous system is not required to initiate malignant hyperthermia (MH). Recently it has been shown that K+-induced contractures in certain skeletal and cardiac muscles might not be determined only by cellular membrane potential changes predicted by the tendency for K+ to move in accord with its electrical and concentration gradients [3, 12]. We report here that normal and diseased skeletal muscles respond differently to raised external K+, which supports the idea that the onset of the MH syndrome is determined by a defect associated with a site in muscle cells superficial to the cytoplasm rather than, as has been suggested, within the cell or in the nervous system [7]. In addition, we find that porcine skeletal muscles, like certain other muscles, produce much less force in K+ than expected from our measurements of the relationship between membrane potential and external K+.

Animals↗
PubMed1982

Branched skeletal muscle fibers not associated with dysfunction.

We report the occurrence of large clefts and branches in some amphibian vertebrate skeletal muscle fibers. Such fibers can be isolated intact from various skeletal muscles of fully mature animals and apparently are normal in other respects. Electron micrographs showed no signs of degeneration in most fibers. Electrical and mechanical studies revealed that all branches were excitable and able to contract. Branches evidently can arise in the absence of abnormal influences such as experimentally induced overload. The apparent cause may be either fusion or splitting of fibers.

Animals↗
PubMed1982

Block of squid axon K channels by internally and externally applied barium ions.

We have studied the interactions of Ba ion with K channels. Ba2+ blocks these channels when applied either internally or externally in millimolar concentrations. Periodic depolarizations enhance block with internal Ba2+, but diminish the block caused by external Ba2+. At rest, dissociation of Ba2+ from blocked channels is very slow, as ascertained by infrequent test pulses applied after washing Ba2+ form either inside or outside. The time constant for recovery from internal and external Ba2+ is the same. Frequent pulsing greatly shortens recovery time constant after washing away both Ba2+in and Ba2+out. Block by Ba2+ applied internally or externally is voltage dependent. Internal Ba2+ block behaves like a one-step reaction governed by a dissociation constant (Kd) that decreases e-fold/12 mV increase of pulse voltage: block deepens with more positive pulse voltage. For external Ba2+, Kd decreases e-fold/18 mV as holding potential is made more negative: block deepens with increasing negativity. Millimolar external concentrations of some cations can either lessen (K+) or enhance (NH+4, Cs+) block by external Ba2+. NH+4 apparently enhances block by slowing exist of Ba ions from the channels. Rb+ and Cs+ also slow clearing of Ba ions from channels. We think that (a) internally applied Ba2+ moves all the way through the channels, entering only when activation gates are open; (b) externally applied Ba2+ moves two-thirds of the way in, entering predominantly when activation gates are closed; (c) at a given voltage, Ba2+ occupies the same position in the channels whether it entered from inside or outside.

Animals↗
PubMed1982

Calcium in excitation--contraction coupling of frog skeletal muscle.

A principal step in the process leading to muscle contraction is the intracellular release of Ca2+. We have detected and compared some physical and chemical events that reflect Ca2+ release in contracting frog skeletal muscle cells, described the effects of some agents that are believed to alter intracellular Ca2+ release during contraction, and speculated about the role of Ca2+ release in influencing some of the mechanical properties of frog muscle. The specific physical features recorded were changes in striation spacing, myofibrillar orientation, and force development. The chemical feature was the relative change in intracellular [Ca2+] recorded as light emission from cells microinjected with the Ca2+-sensitive protein aequorin. The presence or absence of a correlation among these variables has been used (i) to evaluate the action of some agents thought to change intracellular Ca2+ release in excitation--contraction (E--C) coupling, (ii) to further substantiate the effects of cell length on Ca2+ release, and (iii) to examine some details of models for E--C coupling. The results showed that potentiating agents enhance and prolong intracellular Ca2+ release without changing the rate of Ca2+ removal during E--C coupling. This extra Ca2+ does not produce the same effect on contractions at all lengths. Contractility is inversely related to cell length, and Ca2+-induced activation is normally less than maximum not only at short lengths but also at optimal striation spacings.

Aequorin↗
PubMed1981

Skeletal muscle: length-dependent effects of potentiating agents.

The ability of vertebrae skeletal muscle to contract more vigorously than normal in the presence of potentiating agents depends on the initial length of a muscle cell. Other factors such as the intracellular calcium ion transient, temperature, chemical nature of the potentiating agent, and the ratio of intrinsic twitch to tetanic force influence the degree of contractile potentiation but cannot account for the length dependence. At least part of a muscle cell seems normally less than fully active during contractions not only at short lengths but also at optimal sarcomere lengths.

Aequorin↗
PubMed1981

Calcium transients in asymmetrically activated skeletal muscle fibers.

Skeletal muscle fibers of the frog Rana temporaria were held just taut and stimulated transversely by unidirectional electrical fields. We observed the reversible effects of stimulus duration (0.1-100 ms) and strength on action potentials, intracellular Ca2+ transients (monitored by aequorin), and contractile force during fixed-end contractions. Long duration stimuli (e.g., 10 ms) induced a maintained depolarization on the cathodal side of a cell and a maintained hyperpolarization on its anodal side. The hyperpolarization of the side facing the anode prevented the action potential from reaching mechanical threshold during strong stimuli. Variation of the duration or strength of a stimulus changed the luminescent response from a fiber injected with aequorin. Thus, the intracellular Ca2+ released during excitation-contraction coupling could be changed by the stimulus parameters. Prolongation of a stimulus at field strengths above 1.1 x rheobase decreased the amplitude of aequorin signals and the force of contractions. The decreases in aequorin and force signals from a given fiber paralleled one another and depended on the stimulus strength, but not on the stimulus polarity. These changes were completely reversible for stimulus strengths up to at least 4.2 x rheobase. The graded decreases in membrane depolarization, aequorin signals, and contractile force were correlated with the previously described folding of myofibrils in fibers allowed to shorten in response to the application of a long duration stimulus. The changes in aequorin signals and force suggest an absence of myofilament activation by Ca2+ in the section of the fiber closest to the anode. The results imply that injected aequorin distributes circumferentially in frog muscle with a coefficient of at least 10(-7) cm2/s, which is not remarkably different from the previously measured coefficient of 5 x 10(-8) cm2/s for its diffusion lengthwise.

Action Potentials↗
PubMed1980

Interaction of barium ions with potassium channels in squid giant axons.

Blocking of potassium channels by internally and externally applied barium ions has been studied in squid giant axons. Internal Ba (3-5 mM) causes rapid decay or "inactivation" of potassium current (IK). The kinetics and degree of block are strongly voltage-dependent. Large positive voltages speed blocking and make it more profound. Raising the external potassium concentration (Ko) from 0 to 250 mM has the opposite effect: block is made slower and less severe. In contrast, for positive voltages block by the tetraethylammonium derivative 3-phenylpropyltriethylammonium ion is almost independent of Ko and voltage. Recovery from block by internal Ba has a rapid phase lasting a few milliseconds and a slow phase lasting approximately 5 min. Internal Ba causes a "hook" in the IK tails recorded on repolarizing the fiber in high potassium external medium. External Ba, on the other hand, blocks without much altering IK time-course. KD (the dissociation constant) for block by external Ba is a few millimolar, and depends on the internal potassium concentration, the holding potential, and other factors. A reaction scheme for Ba and K channels is presented, postulating that internal and external Ba reach the same point in the channel. Once there, Ba blocks and also stabilizes the closed conformation of the channel. The extreme stability of the Ba channel complex implies the existence of negative charge within the channel.

Animals↗
PubMed1980

Porcine muscle responses to carbachol, alpha- and beta-adrenoceptor agonists, halothane or hyperthermia.

1. Whole body trans-section at the level of the first or second lumbar vertebra of stress-susceptible or normal Poland China swine provided a preparation of isolated perfused caudal muscle that was without nervous or hormonal influences. Metabolic responses to halothane anaesthesia were exaggerated in the susceptible preparation. 2. Carbachol (10(-4) M) increased O2 consumption threefold and elevated blood lactate levels from 3 to 8 mumole/ml. in susceptible but not in normal muscle preparations. 3. Isoprenaline in a continuous infusion (2.5 micrograms/kg caudal wt. per min for 12 min, subsequently diminished to 1.2 microgram/kg per min) did not increase O2 consumption of susceptible or normal muscle but did increase blood lactate by 2 mumole/ml. in both. 4. Simultaneous administration of carbachol and isoprenaline resulted in additive increases in blood lactate. 5. Incremental increases in temperature above 41 degrees C initiated exaggerated increases in O2 consumption and blood lactate in susceptible but not normal muscle; these were similar to whole body responses. 6. Phenylephrine (0.2-25 micrograms/kg per min continuous) produced (i) hypertension, (ii) no observed effects upon aerobic or anaerobic metabolism and (iii) progressive tissue oedema; these effects were similar in susceptible and normal muscle. 7. Skeletal muscle from stress-susceptible swine is evidently inherently capable of metabolic responses to cholinergic agonists and increased temperature; these responses are greater than those in normal muscle. This suggests that initiation of stress responses in intact swine is related to somatic motor and sympathetic stimulation of abnormal skeletal muscle, and not to a disorder of the somatic or sympathetic nervous system.

Animals↗
PubMed1979

Skeletal muscle sarcoplasmic reticulum in porcine malignant hyperthermia.

To examine the function of sarcoplasmic reticulum (SR) in malignant hyperthermia, SR was isolated from semitendinosus muscle of normal and genetically susceptible Poland China swine. Determinations included rate of calcium binding (oxalate absent), rate and capacity of calcium uptake (oxalate present), and spontaneous calcium release (in the absence of ionic depolarization or calcium) with and without halothane, using the millipore filtration technique. Rate of calcium binding, and rate and capacity of calcium uptake were decreased, and spontaneous calcium release was greater in SR fragments from susceptible swine as compared to those from normal swine. Halothane 0.5% slightly increased the rate of calcium binding in susceptible and normal SR. Above 1%, halothane decreased calcium binding rate, and uptake rate and capacity, and increased calcium release similarly in susceptible and normal SR. These differences in SR function were insufficient to explain the etiology of malignant hyperthemia, nor did the effect of halothane account for its triggering action.

Animals↗
PubMed1978

Calcium transients in isolated amphibian skeletal muscle fibres: detection with aequorin.

1. Single twitch muscle fibres isolated from frogs and toads were microinjected with the Ca2+-sensitive bioluminescent protein aequorin. The fibres contracted normally and emitted flashes of light (aequorin responses) in response to stimulation for many hours thereafter. 2. No luminescence was detected from healthy fibres at rest. 3. The aequorin diffused from the site of injection at a rate consistent with a diffusion coefficient of 5 x 10(-8) cm2/sec. 4. During trains of isometric contractions there was a progressive reduction in both the amplitude and the rate of decline of the aequorin response, an observation consistent with the theory that Ca is redistributed from sites of release to sites of sequestration under such circumstances. 5. In isometric tetani light emission continued to rise long after the plateau of force had been achieved. This and the fact that the amplitude of the tetanic aequorin response increased steeply with increasing stimulus frequency suggest that in tetani the sarcoplasmic [Ca2+] may normally be above the level required to saturate the contractile apparatus. 6. Both in twitches and in tetani the amplitude of the aequorin response increased slightly and then decreased substantially as the fibre was stretched progressively beyond slack length. 7. In potassium contractures the luminescent and mechanical responses first became detectable at about the same [K+], but for equivalent force luminescence was less intense than in twitches. The aequorin response was biphasic in solutions of high [K+]. 8. Exposure of the fibre to Ca2+-free solutions had no influence on either the mechanical or the luminescent responses in twitches. In Ca2+-free solutions tetanic aequorin responses tended not to be maintained as well as normally, suggesting that intracellular Ca stores do become somewhat depleted. 9. In twitches the amplitude of the aequorin response probably reflects the amount of Ca2+ liberated into the cytoplasm rather than a [Ca2+] in equilibrium with the myofilaments. Changes in the rate of decay of the aequorin response may reflect changes in the rate of Ca sequestration by the sarcoplasmic reticulum. 10. In K+-contractures and during the plateaus of tetani the aequorin signal changes slowly enough so that it seems unlikely that substantial gradients of [Ca2+] exist at the sarcomere level. Under such circumstances the amplitude of the aequorin response probably does reflect the [Ca2+] in equilibrium with the myofilaments.

Aequorin↗
PubMed1976

Vertebrate striated muscle: length dependence of calcium release during contraction.

It is well known that the force-generating ability of vertebrate striated muscle depends upon its length. At lengths longer than the optimum there is a close correlation between decreasing overlap of the myofilaments and the lessening of contractile force, but at lengths shorter than the optimem additional factors may contribute to decreased contracility. For example, the release of calcium into the myofilament space is decreased during contractions at short muscle lengths, and the morphological changes seen in light and electron micrographs of shortening fibers suggest that the decreased calcium release occurs in the core of the fiber. This length dependent change in calcium release may be one of the factors determining the decrease in contractility with shortening.

Animals↗