Decreased defibrillator-induced dysfunction with biphasic rectangular waveforms

1984 ◽  
Vol 247 (5) ◽  
pp. H792-H796 ◽  
Author(s):  
J. L. Jones ◽  
R. E. Jones
Keyword(s):  
Cell Membrane ◽  
Contractile Activity ◽  
Myocardial Cell ◽  
Myocardial Cells ◽  
Initial Portion ◽  
Electric Shocks ◽  
Percent Success ◽  
Low Amplitude ◽  
Cultured Myocardial Cells

High-intensity electric shocks used for cardiac defibrillation produce arrhythmias, S-T segment changes, and a low percent success in situ. Cultured myocardial cells exhibit similar postshock arrhythmias that are caused by a prolonged depolarization of the cell membrane. Since this dysfunction is ameliorated by biphasic RLC-type waveforms, we examined rectangular biphasic waveforms to maximize this beneficial effect and clarify the dysfunction-inducing mechanism. Cultured myocardial cells were subjected to electric field stimulation with monophasic 5-ms rectangular waveforms of about 80 V/cm to produce a postshock arrest of contractile activity lasting 4 s. Shocks given with this control waveform were alternated with biphasic test waveforms having the same initial portion followed by negative "tails" 1-100 ms in duration and 5-100% of the initial positive portion in amplitude. Results from 31 biphasic waveforms demonstrated significant alterations in postshock dysfunction. Waveforms with up to 10% undershoot and ranging from 5 to 100 ms in duration decreased arrest time by up to 50%; waveforms with greater than 20% undershoot led to protracted postshock arrest times. These results strengthen the hypothesis that electromechanical breakdown of the myocardial cell membrane underlies postshock dysfunction and show that biphasic waveforms with low amplitude tails ameliorate this dysfunction.

Improved defibrillator waveform safety factor with biphasic waveforms

1983 ◽  
Vol 245 (1) ◽  
pp. H60-H65 ◽  
Author(s):  
J. L. Jones ◽  
R. E. Jones
Keyword(s):  
Safety Factor ◽  
Voltage Gradient ◽  
Excitation Threshold ◽  
Efficacy And Safety ◽  
Myocardial Cells ◽  
Safety Factors ◽  
Adult Type ◽  
Intracellular Microelectrodes ◽  
Cultured Myocardial Cells

Excitation thresholds and arrhythmias were studied in "adult-type" cultured chick embryo myocardial cells after electric field stimulation with biphasic, truncated, and rectified underdamped RLC (resistance-inductance-capacitance) type waveforms, to test the hypothesis that the negative phase of biphasic waveforms ameliorates membrane dysfunction induced by the initial positive portion. Photocell mechanograms and intracellular microelectrodes monitored extrasystoles and depolarization-induced arrhythmias. Rectifying or truncating biphasic waveforms did not alter the excitation threshold. However, shock intensities producing specific postshock arrhythmias or a specific severity of postshock prolonged depolarization differed significantly when biphasic waveforms were truncated or rectified. The voltage gradient producing a specific dysfunction was 12-14% lower for the truncated version than for the biphasic; that for the rectified version was 17-27% lower than for the biphasic version (although both contained the same energy). Safety factor, the ratio between shock intensity producing specific dysfunction and that producing excitation, was determined for each waveform. Biphasic waveforms had larger safety factors than truncated or rectified waveforms. Since safety factor, as measured in cultured myocardial cells, closely corresponds with in situ defibrillating effectiveness (14), the significantly higher safety factors of biphasic waveforms suggest that carefully shaped biphasic waveforms might improve the efficacy and safety of cardiac defibrillation procedures.

The role of (bio)surfactant sorption in promoting the bioavailability of nutrients localized at the solid-water interface

1999 ◽  
Vol 39 (7) ◽  
pp. 91-98 ◽  
Author(s):  
Ryan N. Jordan ◽  
Eric P. Nichols ◽  
Alfred B. Cunningham
Keyword(s):  
Mass Transfer ◽  
Cell Membrane ◽  
Substrate Concentration ◽  
Water Interface ◽  
Industrial Systems ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Surfactant Sorption

Bioavailability is herein defined as the accessibility of a substrate by a microorganism. Further, bioavailability is governed by (1) the substrate concentration that the cell membrane “sees,” (i.e., the “directly bioavailable” pool) as well as (2) the rate of mass transfer from potentially bioavailable (e.g., nonaqueous) phases to the directly bioavailable (e.g., aqueous) phase. Mechanisms by which sorbed (bio)surfactants influence these two processes are discussed. We propose the hypothesis that the sorption of (bio)surfactants at the solid-liquid interface is partially responsible for the increased bioavailability of surface-bound nutrients, and offer this as a basis for suggesting the development of engineered in-situ bioremediation technologies that take advantage of low (bio)surfactant concentrations. In addition, other industrial systems where bioavailability phenomena should be considered are addressed.

scholarly journals DnaA, the Initiator of Escherichia coliChromosomal Replication, Is Located at the Cell Membrane

2000 ◽  
Vol 182 (9) ◽  
pp. 2604-2610 ◽  
Author(s):  
Gillian Newman ◽  
Elliott Crooke
Keyword(s):  
Cell Membrane ◽  
Spatial Organization ◽  
Active Form ◽  
Chromosomal Replication ◽  
E Coli ◽  
Dnaa Protein ◽  
Section Electron ◽  
Acidic Phospholipids

ABSTRACT Given the lack of a nucleus in prokaryotic cells, the significance of spatial organization in bacterial chromosome replication is only beginning to be fully appreciated. DnaA protein, the initiator of chromosomal replication in Escherichia coli, is purified as a soluble protein, and in vitro it efficiently initiates replication of minichromosomes in membrane-free DNA synthesis reactions. However, its conversion from a replicatively inactive to an active form in vitro occurs through its association with acidic phospholipids in a lipid bilayer. To determine whether the in situ residence of DnaA protein is cytoplasmic, membrane associated, or both, we examined the cellular location of DnaA using immunogold cryothin-section electron microscopy and immunofluorescence. Both of these methods revealed that DnaA is localized at the cell membrane, further suggesting that initiation of chromosomal replication in E. coli is a membrane-affiliated event.

PPARγ Agonist Ameliorates the Impaired Fluidity of the Myocardial Cell Membrane and Cardiac Injury in Hypercholesterolemic Rats

2015 ◽  
Vol 17 (1) ◽  
pp. 25-34 ◽  
Author(s):  
Ye Wu ◽  
Xiutao Tan ◽  
Jue Tian ◽  
Xin Liu ◽  
Yehong Wang ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Cardiac Injury ◽  
Myocardial Cell ◽  
Pparγ Agonist

Chronic effects of ethanol on cultured myocardial cells: ultrastructural and morphometric studies

2003 ◽  
Vol 442 (4) ◽  
pp. 356-363 ◽  
Author(s):  
Keiko Mashimo ◽  
Shigeru Sato ◽  
Youkichi Ohno
Keyword(s):  
Myocardial Cells ◽  
Chronic Effects ◽  
Cultured Myocardial Cells

Surface Features of Striated Muscle

1968 ◽  
Vol 3 (4) ◽  
pp. 467-474
Author(s):  
D. G. RAYNS ◽  
F. O. SIMPSON ◽  
W. S. BERTAUD
Keyword(s):  
Striated Muscle ◽  
Myocardial Cell ◽  
Fracture Plane ◽  
Myocardial Cells ◽  
General Survey ◽  
Inner Surface ◽  
Ordered Array ◽  
Capillary Endothelial Cells ◽  
Pinocytotic Vesicles ◽  
T Tubules

A general survey of guinea-pig myocardium was undertaken using the freeze-etch technique. Replicas of myocardial cell membranes were obtained. These showed an ordered array of pits or stumps situated at Z levels. The pits are interpreted as the apertures of the transverse tubules (T-tubules) seen from outside the cell, and the stumps as the remnants of the T-tubules remaining attached to the cell membrane after the cell contents have been removed. Pinocytotic vesicles were also present. T-tubules, mitochondria and myofilaments could be seen in replicas of the interior of myocardial cells. Capillary endothelial cells were seen from various aspects; pinocytotic vesicles were their most prominent feature. The appearances of the cell membrances in the present study suggest that the fracture plane tends to pass along either the outer or the inner surface of the membrane rather than of split the membrane.

Effects of trypsin on the in situ identification of epidermal cell membrane antigens

1987 ◽  
Vol 14 (6) ◽  
pp. 331-336 ◽  
Author(s):  
G. Zambruno ◽  
V. Gielen ◽  
D. Schmitt ◽  
C. Dezutter-Dambuyant ◽  
J. Thivolet
Keyword(s):  
Cell Membrane ◽  
Epidermal Cell ◽  
Membrane Antigens ◽  
Cell Membrane Antigens
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