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Biomedical subjects

A M Gordon

Publications and source records attributed to A M Gordon.

At least 91 records · Page 5Linked to original sources
PubMed1989

Removal of tropomyosin overlap modifies cooperative binding of myosin S-1 to reconstituted thin filaments of rabbit striated muscle.

Cooperative binding of myosin S-1.ADP to regulated F-actin was previously reported and has been interpreted by a two-state model in which an important source of cooperativity is nearest neighbor interactions between the 7-actin.tropomyosin (TM).troponin units (functional units) (Hill, T.L., Eisenberg, E., and Greene, L. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 3186-3190). It has been postulated that the head-to-tail overlap between adjacent TM molecules is the structural basis of the nearest neighbor interactions. We tested the hypothesis by examining S-1.ADP binding to reconstituted regulated F-actin containing either intact TM or nonpolymerizable TM from which the COOH-terminal 11 residues were removed. In the absence of Ca2+, substitution of nonpolymerizable TM for TM reduced significantly the slope of the steeply rising phase of the sigmoidal S-1.ADP binding curve. Nevertheless, considerable residual cooperativity remained. Analysis of the data using the two-state model of Hill et al. suggests that removal of TM overlap abolishes nearest neighbor interactions, while the concerted change of the state of 7 actins in a functional unit can account for the residual cooperativity.

Actin Cytoskeleton↗
PubMed1989

Effect of landfill leachate irrigation on red maple (Acer rubrum L.) and sugar maple (Acer saccharum Marsh.) seedling growth and on foliar nutrient concentrations.

Greenhouse experiments were conducted to investigate the nature and severity of stresses imposed on northern hardwood tree species (red maple (Acer rubrum L.) and sugar maple (Acer saccharum Marsh.)) by the application of municipal landfill leachate. Red maple seedlings received applications of untreated and pretreated (lime, activated carbon) leachate, to both leaves and soil, at irrigation rates consistent with evapotranspirational demands. Plant height measurements indicated no significant growth effects arising from leachate application over a 7-week period. Stem diameter, however, was positively affected by applications of both untreated and lime-treated leachate diluted to 75% with deionized water. Iron foliar concentrations were significantly higher in seedlings irrigated with untreated leachate applied to leaves and soil, but not in seedlings where leachate was applied to soil only. Nitrogen foliar concentrations were substantially higher in seedlings receiving undiluted and untreated leachate applied to the soil only. The Cu concentration of the red maple foliage decreased appreciably in plants receiving moderate applications of leachate. Foliar Ca concentrations decreased notably in seedlings irrigated with untreated leachate applied to the soil and with diluted, carbon-treated leachate. The Cu concentration of the red maple foliage decreased appreciably in plants receiving applications of undiluted and 50% water-diluted lime-treated leachate while Mn levels were consistently high across all treatments. Leachate application did not cause any discernable changes in foliar concentrations of P, K, Mg, B or Zn. In an ancillary experiment, sugar maple seedlings were subjected to saturation/ drainage treatment cycles with undiluted and untreated leachate. Severe visible symptoms of vegetative stress were apparent within 24 h and 100% seedling mortality occurred after five such waterlogging cycles. Fe assimilation was apparent in both leachate treatments relative to the 24 h water treatment. Despite the short-term nature of the experiments, the results indicate how quickly forest vegetation may respond to altered chemical environments. This underscores the need for correct installation and control of leachate irrigation systems.

Journal Article↗
PubMed1989

Influence of fiber type and muscle source on Ca2+ sensitivity of rat fibers.

This study investigated the influence of muscle source and fiber type on the calcium sensitivity of skinned rat skeletal muscle fibers from predominantly slow muscles [soleus (SOL) and adductor longus (AL)], mixed muscle [posterior gracilis (PG)], and predominantly fast-twitch muscle [extensor digitorum longus (EDL)]. Fibers were characterized histochemically and by one-dimensional protein gel electrophoresis, and calcium-tension relationships were determined. Fiber type and muscle source had significant effects on the negative log of the calcium concentration associated with half-maximal tension (pCa1/2). Slow-twitch fibers had larger values of pCa1/2 than did fast-twitch fibers. Slow-twitch fibers from the predominantly slow muscles, SOL and AL, had similar values of pCa1/2 but slightly smaller values than from the mixed muscle, PG. Fast-glycolytic (FG) fibers from the predominantly fast muscle, EDL, had a higher pCa1/2 than fibers from the mixed fiber type muscle, PG. There were no differences between the pCa1/2 associated with FG and fast-oxidative-glycolytic fibers.

Adenosine Triphosphatases↗
PubMed1988

Partial purification of the sodium- and potassium-coupled L-glutamate transport glycoprotein from rat brain.

The sodium- and potassium-coupled L-glutamate transporter from rat brain has been solubilized with cholate and 10-20-fold purified using Wheat Germ Agglutinin-Sepharose 4B. Transport activity--as determined upon reconstitution of the fraction into liposomes--was retained on the column and eluted by N-acetylglucosamine. When the glycoprotein fraction was depleted of the N-acetylglucosamine and applied to a second round of lectin-chromatography, the L-glutamate transport activity was retained and again could be eluted by the sugar. The transporter activity reconstituted from the glycoprotein fraction exhibited the same features as that in synaptic plasma membranes, including electrogenicity, an absolute dependence on external sodium and internal potassium, affinity and stereospecificity. Furthermore, efflux and exchange properties of the reconstituted preparation were also unchanged by the solubilisation and lectin-chromatography. These observations indicate that the sodium- and potassium-coupled L-glutamate transporter is a glycoprotein and is predominantly reconstituted in the 'right-side-out' conformation.

Amino Acid Transport System X-AG↗
PubMed1988

Length and myofilament spacing-dependent changes in calcium sensitivity of skeletal fibres: effects of pH and ionic strength.

The calcium sensitivity of force was measured in glycerinated rabbit psoas fibres at sarcomere lengths (SL) from 2.3 to 3.4 micron. Increased SL caused calcium sensitivity to increase and the slope of force-calcium relations to decrease. We have hypothesized that length-dependent changes in myofilament lattice spacing and the presence of fixed charge on the myofilaments are important in determining calcium sensitivity. Lattice spacing changes were monitored by measuring fibre diameter (D). D was decreased by increasing SL, decreasing bathing solution pH and by osmotic compression with 3% PVP. 3% PVP caused D to decrease by about 15% at all SLs and pH values tested. Force-calcium relations were measured at different SLs and pH values, with and without 3% PVP in the bathing solutions. At all pH values D at SL 2.3 micron with 3% PVP was comparable to the value at 3.4 micron, without PVP. At pH 7.5 and 7.0 calcium sensitivity was about the same at both SL, although the slope of the force-calcium relation was less at longer SL. The similarity of the calcium sensitivity at the same D, but much different SL, indicates that lattice spacing is important in determining calcium sensitivity, while SL and the degree of myofilament overlap are important in determining the slope of force-calcium relations. In order to test for the role of myofilament charge in determining calcium sensitivity, pH and ionic strength were varied. Decreasing pH caused decreased maximum force and calcium sensitivity. In addition, the influence of SL on calcium sensitivity decreased as pH was lowered, with minimal SL dependence at pH 5.5; even though lattice spacing still decreased with increasing SL. When D was decreased with PVP, calcium sensitivity increased at all SLs in pH 7.5 and 7.0 while the same lattice spacing changes at pH 6.0 and 5.5 resulted in greatly reduced shifts in calcium sensitivity. These results indicate that the effect of lattice spacing on calcium sensitivity depends on myofilament charge. At pH 6.0, even though osmotic compression of the lattice has no effect, increasing SL causes about half the shift in calcium sensitivity seen at pH 7.0. Lowering ionic strength from 200 to 110 mM caused an increase in both the magnitude and length dependence of calcium sensitivity at pH 7.0, while at pH 5.5 both decreased.(ABSTRACT TRUNCATED AT 400 WORDS)

Actin Cytoskeleton↗
PubMed1988

Muscle force and stiffness during activation and relaxation. Implications for the actomyosin ATPase.

Isolated skinned frog skeletal muscle fibers were activated (increasing [Ca2+]) and then relaxed (decreasing [Ca2+]) with solution changes, and muscle force and stiffness were recorded during the steady state. To investigate the actomyosin cycle, the biochemical species were changed (lowering [MgATP] and elevating [H2PO4-]) to populate different states in the actomyosin ATPase cycle. In solutions with 200 microM [MgATP], compared with physiological [MgATP], the slope of the plot of relative steady state muscle force vs. stiffness was decreased. At low [MgATP], cross-bridge dissociation from actin should be reduced, increasing the population of the last cross-bridge state before dissociation. These data imply that the last cross-bridge state before dissociation could be an attached low-force-producing or non-force-producing state. In solutions with 10 mM total Pi, compared to normal levels of MgATP, the maximally activated muscle force was reduced more than muscle stiffness, and the slope of the plot of relative steady state muscle force vs. stiffness was reduced. Assuming that in elevated Pi, Pi release from the cross-bridge is reversed, the state(s) before Pi release would be populated. These data are consistent with the conclusion that the cross-bridges are strongly bound to actin before Pi release. In addition, if Ca2+ activates the ATPase by allowing for the strong attachment of the myosin to actin in an A.M.ADP.Pi state, it could do so before Pi release. The calcium sensitivity of muscle force and stiffness in solutions with 4 mM [MgATP] was bracketed by that measured in solutions with 200 microM [MgATP], where muscle force and stiffness were more sensitive to calcium, and 10 mM total Pi, where muscle force and stiffness were less sensitive to calcium. The changes in calcium sensitivity were explained using a model in which force-producing and rigor cross-bridges can affect Ca2+ binding or promote the attachment of other cross-bridges to alter calcium sensitivity.

Adenosine Triphosphatases↗
PubMed1988

Septic scarlet fever due to Streptococcus pyogenes cellulitis.

We report three cases of septic scarlet fever due to Streptococcus pyogenes Group A (serotype M1/T1/OF-) cellulitis in healthy young adults. Despite prompt treatment two of the patients died. Such cases of cellulitis associated with scarlet fever, severe toxaemia and septicaemia have not been reported in the post-antibiotic era.

Adult↗
PubMed1988

Muscle cross-bridge attachment: effects on calcium binding and calcium activation.

Data from intact and skinned muscle fibers support the hypothesis that cross-bridge interaction modifies TnC structure and calcium activation. Barnacle single muscle fibers microinjected with the calcium bioluminescent photoprotein, aequorin, show extra light (calcium) when shortened during the declining phase of the calcium transient. The extra calcium is increased by increases in muscle force, and its decline is delayed at higher forces. This extra calcium occurs probably because calcium binding to the activating sites is increased by cross-bridge interaction. In rabbit muscle, TnC structure is modified by cross-bridge interaction, since in skinned rabbit psoas muscle fibers TnC extraction is slower at shorter sarcomere lengths, where cross-bridge attachment is increased. Thus the rigor bridges formed in the extraction solution strengthen the attachment of TnC to the thin filament. Reintroduction of TnC, labeled with fluorescent probes near the Ca specific binding sites (Danzylaziridine-DANZ) and Ca-Mg sites (Rhodamine), into the partially TnC extracted fibers allows us to assess the structural changes (total fluorescence for the DANZ probes, linear dichroism for the RHOD probe) in response to calcium binding and cross-bridge attachment. At sarcomere lengths beyond overlap, calcium binding increases the DANZ-TnC fluorescence and disorders the RHOD-TnC label. At full overlap of filaments, rigor cross-bridges also increase the DANZ-TnC fluorescence and RHOD-TnC disorder. The addition of calcium in rigor increases the DANZ-TnC fluorescence little but causes additional RHOD-TnC disorder, although both fluorescence and disorder are increased further in the presence of calcium plus MgATP. In fibers containing DANZ-TnC, decreasing MgATP in the absence of calcium increases both the force and the fluorescence as rigor cross-bridges activate the muscle. In the presence of calcium, an increase in MgATP to 0.75 microM produces a small fluorescent enhancement, but an increase in MgATP to 10 microM and to 3 mM produces a substantial enhancement. The data imply that calcium activates the thin filament, but that the filament is activated further by rigor cross-bridges. Active cross-bridges activate the thin filament still further. Thus, cross-bridges modify TnC structure and calcium activation, with active cross-bridges being more effective than rigor cross-bridges.

Adenosine Triphosphate↗
PubMed1987

Extra calcium on shortening in barnacle muscle. Is the decrease in calcium binding related to decreased cross-bridge attachment, force, or length?

Barnacle single muscle fibers were microinjected with the calcium-specific photoprotein aequorin. We have previously shown (Ridgway, E. B., and A. M. Gordon, 1984, Journal of General Physiology, 83:75-104) that when barnacle fibers are stimulated under voltage clamp and length control and allowed to shorten during the declining phase of the calcium transient, extra myoplasmic calcium is observed. The time course of the extra calcium for shortening steps at different times during the calcium transient is intermediate between those of free calcium and muscle force. Furthermore, the amplitude increases with an increased stimulus, calcium transient, and force. Therefore, the extra calcium probably comes from the activating sites on the myofilaments, possibly as a result of changes in calcium binding by the activating sites. The change in calcium binding may be due, in turn, to the change in muscle length and/or muscle force and/or cross-bridge attachment per se. In the present article, we show that the amount of the extra calcium depends on the initial muscle length, declining at shorter lengths. This suggests length-dependent calcium binding. The relation between initial length and extra calcium, however, parallels that between initial length and peak active force. The ratio of extra calcium to active force is therefore virtually independent of initial length. These data do not distinguish between a direct effect of length on calcium binding and an indirect effect owing to changes in cross-bridge attachment and force through some geometrical factor. The amount of extra calcium increases with the size of the shortening step, tending toward saturation for steps of greater than or equal to 10%. This experiment suggests that calcium binding depends on muscle force or cross-bridge attachment, not just length (if at all). There is much less extra calcium seen with shortening steps at high force when the high force results from stretch of the active muscle than when it results from increased stimulation of muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Reinnervation of skeletal muscle with a neuromuscular pedicle.

In the past decade the otolaryngologist has become interested in the problem of muscle reinnervation as it relates to laryngeal and facial paralysis. Although reinnervation by neuromuscular pedicle transfer has shown promising results in the laboratory and clinic, some investigators have had difficulty in achieving reliable results with this procedure. To further assess the technique's validity, we investigated the neuromuscular pedicle. This study utilized a strap muscle neuromuscular pedicle transfer to a contralateral strap muscle in the rabbit. The results were analyzed by the use of a number of independent measures, including electrical stimulation of the nerve, muscle contractibility, electromyography, enzyme histochemistry, reduced-silver staining for normal fibers, and the retrograde transport of the enzyme marker horseradish peroxidase. The physiologic and anatomic results demonstrated that morphologic and functional reinnervation of the experimentally isolated muscle by the transferred neuromuscular pedicle occurred. The most convincing data were produced by gross electrical stimulation, twitch and tetanic contraction, and horseradish peroxidase labeling. Electromyographic activity and other histologic findings supported the above conclusions.

Animals↗