ELECTRIC IMPEDANCE OF ASTERIAS EGGS

Analysis of Fractional-Order Models Of Polyaniline Doped Polyacrylonitrile Fibres Impedances' (PAN/PANI)

The paper describes the use of electrical impedance spectroscopy (EIS) for characterizing the impedance of polyaniline doped polyacrylonitrile fibres. The electrical impedance of fibres samples was measured by means of high impedance analyser and modeled by four types of models: Debye, Cole-Cole, Davidson-Cole and Havriliak-Negami. The fitting errors are presented for all model types. The model parameters are correlated with chemical substances additives and processing which were used during the fibres production. The presented results show that the fractional-order models reflect properly the impedance spectra of fibres samples.

The excitability of plant cells: with a special emphasis on characean internodal cells

This review describes the basic principles of electrophysiology using the generation of an action potential in characean internodal cells as a pedagogical tool. Electrophysiology has proven to be a powerful tool in understanding animal physiology and development, yet it has been virtually neglected in the study of plant physiology and development. This review is, in essence, a written account of my personal journey over the past five years to understand the basic principles of electrophysiology so that I can apply them to the study of plant physiology and development. My formal background is in classical botany and cell biology. I have learned electrophysiology by reading many books on physics written for the lay person and by talking informally with many patient biophysicists. I have written this review for the botanist who is unfamiliar with the basics of membrane biology but would like to know that she or he can become familiar with the latest information without much effort. I also wrote it for the neurophysiologist who is proficient in membrane biology but knows little about plant biology (but may want to teach one lecture on "plant action potentials"). And lastly, I wrote this for people interested in the history of science and how the studies of electrical and chemical communication in physiology and development progressed in the botanical and zoological disciplines.

Electrical impedance of isolated retina and its changes during spreading depression

The electrical impedance of isolated chick and toad retinas were measured in the absence of, and during, spreading depression, using sinusoidal measuring currents ranging from 10 to 50,000 Hz. Data obtained in the absence of the reaction indicate an electric heterogeneity of the tissue and suggest that at least two groups of cells are responsible for the observed frequency distribution. Spreading depression is accompanied by impedance changes that depend on the frequency of the measuring current and composition of the Ringer's solution. In chick retinas immersed in standard solution, impedance magnitude (Z) as well as phase angle (0) change in phase, displaying an initial increase followed by a longer decrease; in the toad, these changes depend on the measuring frequency: at 10 Hz they are similar to the ones observed in chick retinas, whereas at intermediate and high frequencies they are out of phase. In low Cl- + sucrose Ringer's solution a decrease of impedance is observed in both chick and toad retinas. In low Cl- + Na2SO4 + sucrose Ringer's solution a decrease of impedance also predominates but the Z and 0 curves are biphasic and complex, having time courses which are frequency-dependent. In addition, these changes are different in chick and toad preparations. The experiments show that the impedance changes during the retinal reaction might be related both to extracellular as well as cellular currents. The extracellular current changes could be due to decrease of ionic content and volume of extracellular space, the latter variations being drastically reduced when retinas are immersed in low Cl- solutions. The results also suggest changes of current flow through cellular components which are frequency-dependent: at low frequencies the preferential path being probably through neuronal, and at high frequencies, through glial cells.

Action potential and non-linear current-voltage relation in starfish oocytes

1. The electrical properties of the oocyte membrane of the starfish, Asterina pectinifera, were investigated using an intracellular microelectrode. 2. The resting potential in artificial sea-water ranged from -70 to -80 mV. 3. The starfish oocyte membrane was capable of generating an action potential as a result of permeability increases to both Ca and Na ions.4. The Ca component of the action potential was reversibly suppressed by Co or Mg ions, while the Na component was not affected by tetrodotoxin 5 times 10-minus 6 g/ml. 5. The steady-state relation of voltage vs. current was not linear but S-shaped. The curve wascomposed of inward-going rectification at the membrane potential more negative than -65 mV, outward-going rectification at the potential more positive than OmV and the transitional region between them. These findings are compared with those obtained in the mature egg of the tunicate.