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P J Paolini

Publications and source records attributed to P J Paolini.

11 recordsLinked to original sources
PubMed1994

Sphingosine effects on the contractile behavior of skinned cardiac myocytes.

Sphingosine modulates myocyte beating behavior by acting on the sarcoplasmic reticulum calcium release channel, the ryanodine receptor. Chemically skinned myocytes isolated from adult rabbit ventricles exhibited spontaneous asynchonous contractions in response to micromolar levels of calcium. These cells do not have a functional sarcolemma but exhibit spontaneous contraction-relaxation cycles which are controlled by the sarcoplasmic reticulum. The intracellular second messenger, sphingosine, significantly reduced myocyte beat frequency in a biphasic manner with an IC50 of c. 0.5 microM. A computerized video-enhancement micrography system was used to determine the effect of sphingosine on sarcomere contractile parameters and to determine the potential source of the altered beating behavior produced by sphingosine. Contraction parameters related to sarcomere shortening were unaffected by sphingosine in the submicromolar range, suggesting that sphingosine had no effect on the contractile machinery itself. However, submicromolar sphingosine had a significant inhibitory effect on the spread of activation from sarcomere to sarcomere in these cells. Activation waves were propagated with an average velocity of 331 and 199 microns/s in control and sphingosine (0.58 microM) treated cells, respectively. Permeabilized myocyte calcium uptake was markedly increased by treatment with sphingosine, consistent with an inhibitory effect of sphingosine on sarcoplasmic reticulum calcium release. Sphingosine blocked calcium-induced calcium release from isolated cardiac sarcoplasmic reticulum membranes containing the ryanodine receptor. The results suggest that the site of sphingosine action on calcium signaling and beating behavior in the cardiac cell is the sarcoplasmic reticulum ryanodine receptor. By inhibiting channel opening sphingosine may increase the calcium threshold necessary to trigger calcium-induced calcium release, thus modulating cardiac excitation-contraction coupling.

Animals↗
PubMed1982

The effects of chemical cross-linking agents on calcium-induced structural changes in skinned muscle fibers. Origin within thick filaments detected by optical diffraction methods.

We have reported earlier (Sabbadini, R.A., Rieser, G.D. and Paolini, P.J. (1979) Biochim. Biophys. Acta 578, 526-533) that physiological levels of calcium (pCa 6.95-5.49) can produce structural changes in thick filaments which are detectable as an intensity loss of the first-order optical diffraction lines from chemically skinned skeletal muscle fibers stretched beyond myofilament overlap. We now show that the calcium-induced intensity decrease results from structural changes within, rather than between, thick filaments. Glycerinated, detergent-treated fibers from frog semitendinosus muscle were incubated in 1-10 mM concentrations of dimethylsuberimidate (DMS), dithiobis(succinimidylpropionate) (DTSP) or dimethyl-3,3'-dithiobispropionimidate (DTBP) for 4 h. These substances are homobifunctional lysine-modifying cross-linking reagents known to restrict movement of S-1 heads and limit changes in the association of myosin rods within the core of the thick filament without affecting interfilament lattice spacing. Diffraction patterns from cross-linked cells in relaxing solution were identical to those in control cells, but Ca2+ (pCa 5.49) totally failed to produce the typical 50-70% attenuation of first-order line intensity. Cleavage of the disulfide bond in DTBP-treated cells with dithiothreitol fully restored the Ca2+ sensitivity. Lysine group modification with methylacetimidate, a monofunctional lysine modification reagent equivalent to DMS, did not block the Ca2+ sensitivity. We observed that intensity reductions can also be produced by numerous other agents and mechanisms, such as nonionic polymeric solutions of polyvinylpyrrolidone, which reduces the lattice spacing, and alkaline pH, which probably displaces the S-1 heads from a resting position close to the thick filament surface. However, the prevention of the Ca2+ effect by cross-linkers indicates that intrafilament rather than interfilament changes in structure are responsible for the light diffraction intensity decrease accompanying activation.

Animals↗
PubMed1979

Calcium-induced structural changes in chemically skinned muscle fibers. Detection by optical diffractometry.

The intensity of the first order diffraction line produced by chemically skinned muscle fibers was detected by a self scanning photodiode array and minicomputer system. Line intensity was observed to decrease in fibers stretched to zero filament overlap when subjected to calcium-EGTA buffers in the physiological pCa range. Calcium dependent intensity decreases were not observed for myosin extracted fibers indicating that the thick filament proteins may be the source of the calcium effect seen in non-extracted fibers. These results can be interpreted in terms of calcium dependent effects on thick filament disordering which are not dependent upon cross bridge formation.

Adenosine Triphosphate↗
PubMed1977

Light diffraction studies of sarcomere dynamics in single skeletal muscle fibers.

A position-sensitive optical diffractometer has been used to examine the diffraction spectra produced by single skeletal muscle fibers during twitch and tetanic contraction. First-order diffraction lines were computer-analyzed for mean sarcomere length, line intensity, and percent dispersion in sarcomere length. Line intensity was observed to decrease rapidly by about 60 percent during a twitch, with an exponential recovery to resting intensity persisting well beyond cessation of sarcomere shortening; recovery was particularly prolonged at zero myofilament overlap. A number of single fibers at initial lengths from 2.5 to 3.5 MICRON EXHIBITED a splitting of the first-order line into two or more components during relaxation, with components merging back into a single peak by 200 ms after stimulation. This splitting reflects the asynchronous nature of myofibrillar relaxation within a single fiber. During tetanus, the dispersion decreased by more than 10 percent from onset to plateau, implying a gradual stabilization of sarcomeres.

Animals↗
PubMed1976

Sarcomere length dispersion in single skeletal muscle fibers and fiber bundles.

Light diffraction patterns produced by single skeletal muscle fibers and small fiber bundles of Rana pipiens semitendinosus have been examined at rest and during tetanic contraction. The muscle diffraction patterns were recorded with a vidicon camera interfaced to a minicomputer. Digitized video output was analyzed on-line to determine mean sarcomere length, line intensity, and the distribution of sarcomere lengths. The occurrence of first-order line intensity and peak amplitude maxima at approximately 3.0 mum is interpreted in terms of simple scattering theory. Measurements made along the length of a singel fiber reveal small variations in calculated mean sarcomere length (SD about 1.2%) and its percent dispersion (2.1% +/- 0.8%). Dispersion in small multifiber preparations increases approximately linearly with fiber number (about 0.2% per fiber) to a maximum of 8-10% in large bundles. Dispersion measurements based upon diffraction line analysis are comparable to SDs calculated from length distribution histograms obtained by light micrography of the fiber. First-order line intensity decreases by about 40% during tetanus; larger multifibered bundles exhibit substantial increases in sarcomere dispersion during contraction, but single fibers show no appreciable dispersion change. These results suggest the occurrence of asynchronous static or dynamic axial disordering of thick filaments, with a persistence in long range order of sarcomere spacing during contraction in single fibers.

Animals↗
PubMed1975

Length-dependent optical diffraction pattern changes in frog sartorius muscle.

The length dependence of the laser light diffraction pattern produced by R. pipiens whole sartorius muscle has been examined at rest and during tetanic contraction. The muscle diffraction pattern was scanned by a vidicon camera; camera output was digitized and processed by an on-line digital computer to allow a real line display of a section through the diffraction pattern. Analysis of the first order diffraction line profiles yielded values for line amplitude, intensity, center of gravity, line width and percent dispersion. The calculated dispersion provided a measure of the muscle's sarcomere length distribution. First order line amplitudes and intensities were observed to increase, then decrease, with progressive stretch from 1.0 to 1.3 reference length. The percent dispersion among sarcomeres in resting muscle averaged 11% and was approximately proportional (coefficient = .0341) to length. The amplitude and intensity of zero and first order diffraction lines decreased during tetanus, while the line widths and dispersions increased. First order line intesity during tetanus was maximum at about the same length as during rest, i.e., at approximately 2.5 mu sarcomere length. Sarcomere dispersion increased by about 6% during tetanus.

Animals↗
PubMed1966

Muscle volume changes.

Measurements have been made of the volume changes accompanying single isometric and isotonic twitches of frog sartorius muscle. The volume change consists of a rapid increase, a subsequent decrease, and a return to the initial volume; the order of magnitude of increase and decrease is 10(-5) cc/g of muscle. This volume change is length-dependent: the initial increase becomes more pronounced as the initial length of the muscle is decreased, while the volume decrease is greatest at reference length and is diminished for longer and shorter initial lengths. Muscle volume changes are also dependent upon temperature and amount of shortening: the return phase is prolonged as the temperature is lowered; and, in an isotonic twitch, a volume increase accompanying muscle shortening is superimposed upon the volume change described for an isometric twitch. These "shortening volume changes" may correspond to the volume decrease observed in frog muscle under a passive stretch. If the active state is prolonged by the use of a frog Ringer solution in which iodide ions have been substituted for chloride ions, the time course of the volume decrease is likewise prolonged; this suggests a relationship between the volume decrease and the active state of the muscle.

Animals↗