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J C Lawrence

Publications and source records attributed to J C Lawrence.

At least 145 records · Page 8Linked to original sources
PubMed1984

Insulin action in denervated rat hemidiaphragms. Decreased hormonal stimulation of glycogen synthesis involves both glycogen synthase and glucose transport.

Rat hemidiaphragms were denervated in vivo and then incubated in vitro to assess the ability of insulin to stimulate glycogen synthesis. Denervation for 1 day resulted in 50% decreases in the stimulation by insulin of [U-14C]glucose incorporation into glycogen, and in both the basal and the insulin-stimulated activity ratios (activity minus glucose-6-P/activity plus glucose-6-P) of glycogen synthase; however, the stimulation of 2-deoxyglucose uptake by insulin was not affected by 1 day of denervation. The hormonal stimulation of [U-14C]glucose into glycogen was decreased by 90% after 3 days of denervation. At this time, the stimulation of 2-deoxyglucose uptake by insulin was also reduced and the synthase activity ratios remained depressed. Consistent with its reduced effect on glucose transport, the hormone did not increase glucose-6-P in the 3-day denervated muscles. Furthermore, the Ka for activation of glycogen synthase by glucose-6-P was higher in denervated muscles, and denervation abolished the effect of insulin on decreasing the Ka. The results presented demonstrate that denervation rapidly reduces the extent to which glycogen synthase can be activated by insulin, and has a later effect on decreasing the stimulation of glucose transport. These two effects act synergistically to markedly decrease the hormonal stimulation of glycogen synthesis.

Animals↗
PubMed1984

Tulle-gras dressings.

Tulle-gras backed with a soluble polyvinyl alcohol film has been compared with standard tulle-gras to treat patients with minor burns. The new material although less comformable to body contours offered the advantages of decreased dressing time and improved patient comfort. No adverse effects were observed on wound flora or healing rate.

Adolescent↗
PubMed1984

Evidence that levels of malate dehydrogenase and fumarase are increased by cAMP in rat myotubes.

We have investigated the potential role of adenosine 3',5'-cyclic monophosphate (cAMP) in controlling levels of enzymes of energy metabolism in primary cultures of rat skeletal muscle cells. Incubating myotubes with cholera toxin or forskolin (2 persistent activators of adenylate cyclase) significantly increased the levels of two enzymes of oxidative metabolism, fumarase and malate dehydrogenase. These enzymes were also increased (1.5- to 2.0-fold) by phosphodiesterase inhibitors (caffeine, theophylline, theobromine, 3-isobutyl-1-methylxanthine, papaverine, MJ 1988, Ro 20-1724, or SQ 20009) and the cAMP derivatives: 8-bromo-cAMP or dibutyryl cAMP. In contrast two enzymes of glycolytic metabolism, lactate dehydrogenase and pyruvate kinase, were not consistently affected by these agents. The results presented provide strong evidence that an increase in cAMP can lead to an increase in certain enzymes of oxidative energy metabolism.

Animals↗
PubMed1984

Brain extract induces synaptic characteristics in the basal lamina of cultured myotubes.

The basal lamina (BL) that occupies the synaptic cleft of the skeletal neuromuscular junction is antigenically distinct from extrasynaptic muscle fiber BL, rich in acetylcholinesterase (AChE), and bears projections that form junctional folds in the postsynaptic membrane. We report here that these synapse-specific features of BL are all present at low levels in embryonic rat myotubes cultured without nerve, and that their levels are markedly increased by addition of a soluble extract from adult rat brain. Light and electron microscopic methods show that: (1) antibodies which bind preferentially to synaptic BL in vivo stain small, discrete patches of the myotube's BL; (2) AChE accumulates in patches on the myotube surface; and (3) myotube BL and membrane form invaginations that resemble junctional folds. Patches of BL that bear synaptic antigens, AChE, or folds usually overlie clusters of acetylcholine receptors in the plasma membrane. Myotubes treated with a brain extract bear 5 to 20 times more junctional folds and patches rich in acetylcholine receptors, synaptic BL antigens, and AChE than control myotubes. Together with a previous demonstration that electrical and/or contractile activity can modulate the amount and composition of myotube BL (Sanes, J.R., and J.C. Lawrence, Jr. (1983) Dev. Biol. 97: 123-136), these results suggest that nerves could regulate differentiation of muscle fiber BL by a combination of activity-dependent and -independent mechanisms.

Animals↗
PubMed1983

Multiple phosphorylation of rabbit skeletal muscle glycogen synthase. Evidence for interactions among phosphorylation sites and the resolution of electrophoretically distinct forms of the subunit.

Phosphorylation of rabbit skeletal muscle glycogen synthase by a cyclic nucleotide and Ca2+-independent protein kinase, PC0.7, caused the enzyme to be a better substrate for phosphorylation by another cyclic nucleotide and Ca2+-independent protein kinase, FA/GSK-3. In contrast, phosphorylation by the combination of FA/GSK-3 and cyclic AMP-dependent protein kinase led to less phosphorylation than predicted from the individual actions of the protein kinases. These results are explained in part by the existence of cooperative interactions among the phosphorylation sites of glycogen synthase. Phosphorylation by FA/GSK-3 also correlated with a reduction in the electrophoretic mobility, in the presence of sodium dodecyl sulfate, of the glycogen synthase subunit from an apparent molecular weight of 85,000-86,000 to values of 88,000 and ultimately 90,000. The synergistic phosphorylation by PC0.7 and FA/GSK-3 was associated with an increased formation of the species of reduced electrophoretic mobility. The effects on subunit mobility were also reflected in the behavior of a larger phosphorylated CNBr fragment of glycogen synthase, CB-2, which gave apparent molecular weights of 22,000-27,000 depending on its phosphorylation state.

Animals↗
PubMed1983

Hormonal control of glycogen synthase in rat hemidiaphragms. Effects of insulin and epinephrine on the distribution of phosphate between two cyanogen bromide fragments.

The effects of insulin and epinephrine on the phosphorylation of glycogen synthase were investigated using rat hemidiaphragms incubated with [32P]phosphate. Antibodies against rabbit skeletal muscle glycogen synthase were used for the rapid purification of the 32P-labeled enzyme under conditions that prevented changes in its state of phosphorylation. The purified material migrated as a single radioactive species (Mapp = 90,000) when subjected to electrophoresis in sodium dodecyl sulfate. Insulin decreased the [32P]phosphate content of glycogen synthase. This effect occurred rapidly (within 15 min) and was observed with physiological concentrations of insulin (25 microunits/ml). The amount of [32P]phosphate removed from glycogen synthase by either different concentrations of insulin or times of incubation with the hormone was well correlated to the extent to which the enzyme was activated. Epinephrine (10 microM) inactivated glycogen synthase and increased its content of [32P]phosphate by about 50%. Cleavage of the immunoprecipitated enzyme with cyanogen bromide yielded two major 32P-labeled fragments of apparent molecular weights equal to approximately 28,000 and 15,000. The larger fragment (Fragment II) displayed electrophoretic heterogeneity similar to that observed with the corresponding CNBr fragment (CB-2) from purified rabbit skeletal muscle glycogen synthase phosphorylated by different protein kinases. Epinephrine increased [32P]phosphate content of both fragments; however, the increase in the radioactivity of the smaller fragment (Fragment I) was more pronounced. Insulin decreased the amount of [32P] phosphate present in Fragments I and II by about 40%. The results presented provide direct evidence that both insulin and epinephrine control glycogen synthase activity by regulating the phosphate present at multiple sites on the enzyme.

Animals↗
PubMed1983

Activity-dependent accumulation of basal lamina by cultured rat myotubes.

Myoblasts from 20-day rat embryos fuse and differentiate in culture to form spontaneously active myotubes. The myotubes acquire an extracellular matrix that includes a patchy basal lamina (BL) and a layer of fibrils that runs among and above the cells. Several antibodies that bind to muscle fiber basement membrane in vivo were used to study the organization of the extracellular matrix and the effect of muscle activity on the accumulation of its components. Light and electron microscopic immunohistochemical methods showed that the composition and organization of myotube BL in vitro resemble those seen in vivo. Antibodies that bind to both synaptic and extrasynaptic muscle fiber BL, in vivo stain the entire myotube BL in vitro, while antisera that bind preferentially to synaptic BL in vivo stain small patches of myotube BL, which are usually associated with regions rich in acetylcholine receptors. The effects of activity on accumulation of BL were studied by comparing control myotubes to myotubes paralyzed with tetrodotoxin or lidocaine. Immunohistochemical and 125I-antibody binding experiments with three antisera that stain the entire BL showed that paralyzed myotubes accumulate less BL than active myotubes. The effects of activity and inactivity are reversible: new BL forms if toxin is removed from cultures and BL is lost if active myotubes are paralyzed. Thus, accumulation of BL by myotubes is dependent, at least in part, on activity. In contrast, the number of patches stained by synapse-specific BL antibodies is increased in inactive cultures. Thus, immunologically distinguishable components of BL are differentially affected by activity.

Animals↗
PubMed1983

Levels of enzymes of energy metabolism are controlled by activity of cultured rat myotubes.

We have investigated the effects of inhibiting the spontaneous activity of cultured rat myotubes on several representative enzymes of glycolytic and oxidative metabolism. The results presented demonstrate that contractile activity in the absence of nerves can regulate the amounts of these enzymes and indicate that muscle activity may partially control development of the metabolic types of muscle fibers. Control muscle cells have relatively high levels of glycolytic enzymes and low oxidative enzymes and metabolically most closely resemble fast glycolytic fibers. The divalent cation ionophore A23187 caused enzyme levels of the cultured cells to change towards those found in tonically contracting skeletal muscle fibers in vivo. The evidence presented suggests that calcium may mediate certain of the effects associated with muscle contraction on enzymes of energy metabolism.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1983

A quadruple-lumen intravenous infusion catheter.

A 5 French gauge, 30 cm usable length, radio-opaque, colour-coded quadruple-lumen catheter has been designed for simultaneous multiple central drug infusion and central venous pressure measurement. Concentrated drug infusions can be administered without interruption for pressure measurements. It eliminates the risk of inadvertent bolus administration of concentrated drug solutions during flushing of lines or administration of "push-doses" of other injections into the same infusion line. The problems of chemical incompatibilities and drug interactions are reduced. The system may help reduce complications in patients requiring complex intravenous therapy and pressure measurement.

Blood Pressure Determination↗
PubMed1982

Evaluation of phenoxetol-chlorhexidine cream as a prophylactic antibacterial agent in burns.

A controlled clinical trial was conducted to compare the value of a cream containing 2% phenoxetol and 0.2% chlorhexidine as a prophylactic agent against wound infection in patients with burns affecting up to 15% total body surface area. The acquisition of bacteria was similar in the two treatment groups but the incidence of Staphylococcus aureus in the burns treated with phenoxetol-chlorhexidine cream significantly lower. The incidence of gram-negative bacilli was low in the two treatment groups, and no wound yielded Pseudomonas aeruginosa. Unlike preparations containing silver, phenoxetol-chlorhexidine does not cause electrolyte imbalance or stain materials with which it comes into contact, and it did not produce adverse effects during this trial.

Adolescent↗
PubMed1981

Tetrodotoxin-insensitive sodium channels. Binding of polypeptide neurotoxins in primary cultures of rat muscle cells.

The binding of 125I-labeled derivatives of scorpion toxin and sea anemone toxin to tetrodotoxin-insensitive sodium channels in cultured rat muscle cells has been studied. Specific binding of 125I-labeled scorpion toxin and 125I-labeled sea anemone toxin was each blocked by either native scorpion toxin or native sea anemone toxin. K0.5 for block of binding by several polypeptide toxins was closely correlated with K0.5 for enhancement of sodium channel activation in rat muscle cells. These results directly demonstrate binding of sea anemone toxin and scorpion toxin to a common receptor site on the sodium channel. Binding of both 125I-labeled toxin derivatives is enhanced by the alkaloids aconitine and batrachotoxin due to a decrease in KD for polypeptide toxin. Enhancement of polypeptide toxin binding by aconitine and batrachotoxin is precisely correlated with persistent activation of sodium channels by the alkaloid toxins consistent with the conclusion that there is allosteric coupling between receptor sites for alkaloid and polypeptide toxins on the sodium channel. The binding of both 125I-labeled scorpion toxin and 125I-labeled sea anemone toxin is reduced by depolarization due to a voltage-dependent increase in KD. Scorpion toxin binding is more voltage-sensitive than sea anemone toxin binding. Our results directly demonstrate voltage-dependent binding of both scorpion toxin and sea anemone toxin to a common receptor site on the sodium channel and introduce the 125I-labeled polypeptide toxin derivatives as specific binding probes of tetrodotoxin-insensitive sodium channels in cultured muscle cells.

Aconitine↗