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The effect of length range on heat rate and power during shortening nearin situ length in frog muscle (1986)

Gilbert, Susan H.

Springer

Journal of muscle research and cell motility 7 (1986), S. 115-121

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ISSN: 1573-2657

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Summary Heat rate and tension were measured during the steady state of isovelocity shortening in frog sartorius muscles at two speeds (7.5 and 2.0 mm s−1) through two ranges of the length-tension curve: 1.11 to 1.01L 0and 1.01 to 0.91L 0. Both heat rate and mechanical power were higher at short length than at long length. The ratio of mechanical power to total energy rate was smaller at short length. The difference in heat rates in the two length ranges was greatest during shortening at 7.5 mm s−1 and least during isometric contractions. Calculations were made for two extreme interpretations of the results, based on the assumption that 30% of the isometric maintenance heat rate at optimum length is produced by processes related to activation: (1) that all the difference in heat rate results from effects of length on activation processes and (2) that all the difference results from effects on contractile processes. The rate of heat production by activation processes would have to be 1.5 times higher at short than at long length in an isometric contraction, 1.7 times higher during shortening at 2 mm s−1 and 2.0 times higher at 7.5 mm s−1 to explain the differences in heat rate. The rate of contractile processes would have to be only 1.2 times higher at short than at long length. The results favour the interpretation that the contractile process itself is sensitive to sarcomere length near the plateau of the length-tension curve. The rise in heat rate above the isometric level at 2 mm s−1 did not occur immediately with the beginning of shortening and lagged behind the establishment of steady tension by a few hundred milliseconds. This result indicates that the biochemical steady state is also delayed during shortening.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01753412

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The thermoelastic effect in rigor muscle of the frog (1986)

Gilbert, Susan H. ; Ford, Lincoln E.

Springer

Journal of muscle research and cell motility 7 (1986), S. 35-46

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ISSN: 1573-2657

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Summary Small length changes were imposed on pairs of sartorius muscles fromRana temporaria andRana pipiens in rigor and the mechanical and thermal responses studied. Rigor was induced by soaking the muscles overnight at 0° C in a physiological salt solution containing 1.5m sodium azide and 0.4m sodium iodoacetate. Tension was measured at both the tibial and the pelvic ends of the preparation. Muscles were held at a steady tension of 20 to 76 kN m−2 and stretches or releases of 0.02 to 0.6 mm applied in pairs, with the initial change reversed several hundred milliseconds later. Single stretches resulted in heat absorption and releases in heat production by the preparation. Net heat production resulted from complete cycles of length changes larger than 0.1 mm, whether the initial change was a stretch or a release. The heat produced by the complete cycle was attributed to the movement of the muscles over the thermopile. It was proportional to the difference in tension between the tibial and pelvic ends of the preparation and increased with the size and speed of the length change. Half the heat produced by a complete cycle of length changes was subtracted from the thermal response recorded in the first half-cycle to obtain the reversible component of the response. The reversible component was linearly related to the tension change for all sizes and speeds of length change which were studied, with the heat:tension ratio ranging from −0.0093 to −0.0179 in eleven muscles (mean −0.0128 ± 0.0009). The constancy of the heat:tension ratio in rigor muscles over a wide range of mechanical conditions indicates that the source of the thermal changes is the normal elasticity of the preparation. Since the size of the ratio is approximately the same as that measured in active muscles, the tension-dependent component of the thermal response to length changes applied to active muscles is probably also of elastic origin.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01756200

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Intracellular cyclic AMP produces effects opposite to those of cyclic GMP and calcium on shape and motility of neuroblastoma cells (1992)

Bolsover, Stephen R. ; Gilbert, Susan H. ; Spector, Ilan

New York, NY : Wiley-Blackwell

Cell Motility and the Cytoskeleton 22 (1992), S. 99-116

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ISSN: 0886-1544

Keywords: microinjection ; second messengers ; cytoskeleton ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Medicine

Notes: We have directly evaluated the effects of various intracellular second messengers including cyclic nucleotides, calcium ion, and inositol polyphosphates on shape and motility of differentiating mouse neuroblastoma cells. The messengers were microinjected into cells and the responses of the soma, neurite, and growth cone were monitored using time-lapse video microscopy. Each messenger altered cell shape and motility in a characteristic manner. Cyclic AMP promoted lamellipodial expansion, neurite outgrowth, and motility. The other injected messengers opposed motility. Cyclic GMP caused motile structures to freeze and to retract permanently, while the inhibitory effects of calcium injection were concentrationdependent. Small calcium injections affected specifically actincontaining motile structures which froze and retracted temporarily. Intermediate calcium injections caused a strong contraction at the site of injection in all cells. With large injections, cells retracted long neurites, rounded up, and frequently began vigorous blebbing that continued to cell death. Injections of the inositol polyphosphates 1P3(1,4,5) and IP4(1,4,5,6) mimicked the effects of small calcium injections, as did electrical stimulation that elicited action potentials. The results suggest that in mouse neuroblastoma cells, intracellular CAMP elevation increases cytoskeletal organization and promotes neurite extension perhaps through an enhancement of cell-substratum adhesion. On the other hand, a rise of intracellular cGMP or intracellular calcium interferes directly with the function and organization of the actin-microfilament system. The integrated action of these second messenger systems may, therefore, operate in vivo to allow substances released from neighboring cells to regulate neuronal architecture. © 1992 Wiley-Liss, Inc.

Additional Material: 9 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/cm.970220204

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