Electromotility of outer hair cells from the cochlea of the echolocating bat,Carollia perspicillata

Isolated outer hair cells (OHCs) and explants ot the organ of Corti were obtained from the cochlea of the echolocating bat, Carollia perspicillata, whose hearing range extends up to about 100 kHz. The OHCs were about 10–30 m long and produced resting potentials between-30 to -69 mV. During stimulation with a sinusoidal extracellular voltage field (voltage gradient of 2 mV/m) cyclic length changes were observed in isolated OHCs. The displacements were most prominent at the level of the cell nucleus and the cuticular plate. In the organ of Corti explants, the extracellular electric field induced a radial movement of the cuticular plate which was observed using video subtraction and photodiode techniques. Maximum displacements of about 0.3–0.8 m were elicited by stimulus frequencies below 100 Hz. The displacement amplitude decreased towards the noise level of about 10–30 nm for stimulus frequencies between 100–500 Hz, both in apical and basal explants. This compares well with data from the guinea pig, where OHC motility induced by extracellular electrical stimulation exhibits a low pass characteristic with a corner frequency below 1 kHz. The data indicate that fast OHC movements presumably are quite small at ultrasonic frequencies and it remains to be solved how they participate in amplifying and sharpening cochlear responses in vivo.Abbreviations BM basilar membrane - FFT fast Fourier Transfer - IHC inner hair cell - OHC outer hair cell     

Biotransformation of organic sulfides. Part 9. Formation of (S) para-substituted phenyl methyl sulfoxides by biotransformation usingHelminthosporium species NRRL 4671

Phenyl methyl sulfides substituted in thepara position with methyl, fluoro, chloro, bromo, cyano, nitro, amino, acyl, methoxy, thiomethyl and methylsulfinyl groups have been converted to (S) sulfoxides by biotransformation usingHelminthosporium species NRRL 4671. The highest yields and enantiomeric excesses were obtained with bromo, cyano, methoxy, thiomethyl and methylsulfinyl substituents and in two cases (para-Br and -CN) the products could be crystallized to give (S) sulfoxide of ≥ 96% ee.     

Low cost multi user multi platform accessible HPLC data acquisition system

Summary A low cost multi user multi platform accessible HPLC data acquisition system has been designed for use in a laboratory environment. This system uses available HPLC measurement systems that lack modern network communication tools and a low cost computer with reliable software. HPLC data are portable to any other computer by means of File Transport Protocol (FTP) communication and can then be used for data analysis. Off line analysis of ethanol data showed a substantial improvement over the old system in terms of data accuracy and skewness. Furthermore, off line data analysis could resolve hidden acetaldehyde peaks which revealed to be oscillatory.     

Comparison of techniques for measuring pulse-wave velocity in the rat

Mitchell, Gary F., Marc A. Pfeffer, Peter V. Finn, andJanice M. Pfeffer. Comparison of techniques for measuringpulse-wave velocity in the rat. J. Appl.Physiol. 82(1): 203-210, 1997.We evaluatedmethods for measuring average and regional pulse-wave velocity alongthe full length of the aorta in 18-mo-old ether-anesthetized malespontaneously hypertensive rats. Catheter-tip manometers were placed inthe ascending and descending thoracic aorta via the right carotid andleft femoral arteries, respectively. As the distal catheter waswithdrawn at 1-cm intervals, the relationship between distal catheterinsertion distance and distance between transducers was determined fromthe intercept of the insertion distance vs. transmission delayregression line. Methods that assessed the foot-to-foot time delaybetween pressures accurately predicted the separation between catheters(measured distance of 14.3 cm; intercept of 14.0 ± 0.5 cm;P = not significant) were highlyreproducible (coefficient of variation of 2.3% for repeated measurements) and showed minimal variability (range 509 ± 30 to 600 ± 29 cm/s) along the full length of the aorta. Methods that madeuse of the pressure-pressure transfer function were spatially (range ofvalues along the aorta 367 ± 17 to 722 ± 39 cm/s) and temporally more variable, especially during vasoconstriction with methoxamine, due to the effects of reflected waves.

     

Modeling the population dynamics of annual plants with seed bank and density dependent effects

A model is proposed for the population dynamics of an annual plant (Sesbania vesicaria) with a seed bank (i.e. in which a proportion of seeds remain dormant for at least one year). A simple linear matrix model is deduced from the life cycle graph. The dominant eigenvalue of the projection matrix is estimated from demographic parameters derived from field studies. The estimated values for population growth rate () indicates that the study population should be experiencing a rapid exponential increase, but this was not the case in our population.The addition of density dependent effects on seedling survivorship and adult fecundity, effects for which field studies provide evidence, considerably improves our model. Depending on the demographic parameters, the model leads to stable equilibrium, oscillations, or chaos. Study of the behaviour of this model in the parameter space shows that the existence of a seed bank allows higher among-year variation of adult fecundity, without leaving the region of demographic stability. Field data obtained over 3 years confirm this prediction.     

Involvement of alpha 1- and alpha 2-adrenergic receptors in the hypothalamo-pituitary-ovarian axis of the domestic fowl, Gallus domesticus

The alpha 1-adrenergic receptor ligand, 3H-WB4101, and the alpha 2-adrenergic receptor ligand, 3H-para-aminoclonidine, were utilized at a 1.0 nM incubation concentration to determine relative alpha 1-and alpha 2-adrenergic receptor binding by cell membranes from selected tissues within the brain, ovary and oviduct of the domestic fowl. Significant specific alpha 1-adrenergic binding was observed in the hypothalamus, anterior pituitary, pineal, cerebrum and cerebellum but only the cerebrum had significant alpha 2-receptor binding. Significant levels of alpha 1-adrenergic binding were observed in the granulosa cells of the three largest ovarian follicles and in the postovulatory follicle. Significant specific alpha 2-adrenergic binding was measured in the infundibulum, magnum, isthmus and shell gland of the oviduct. The physiological implications of alpha-adrenergic receptors in these tissues are discussed.     

Preparation of uniform haemoglobin free human erythrocyte ghosts in isotonic solution

A method is described for the preparation of haemoglobin free human erythrocyte ghosts in isotonic solutions using dielectric breakdown technique. In this single haemolytic procedure, almost complete removal of haemoglobin (? 0.1%) was achieved by subjecting the erythrocytes suspended in phosphate buffered, isotonic KCl solution at 0°C to three consecutive electrical field pulses of 16 kV/cm in the presence of 10 mM EDTA; EDTA was used to prevent electrical haemolysis. Haemolysis is induced by subsequent dilution with isotonic and isoionic solution to lower the EDTA concentration. Haemolysis is complete after 5 min; the cells are centrifuged, washed and resuspended in a solution of the same composition and osmolarity containing 4 mM MgCl₂, but no EDTA. The resealing process, carried out at 37°C, was complete in about 1 h. Measurements of the size distribution of the ghost cells in the hydrodynamically focusing Coulter Counter at varying field strengths in the orifice revealed that the ghost population is nearly uniform. The mean (modal) volume of the ghost cells was 110–120 $\text{μ}\text{m}{}^3$ when suspended in phosphate buffered NaCl solution. The apparent breakdown voltage was about 1.3 V.     

Electric field-mediated cell fusion

The use of electrical fields to guide, hold and fuse cells is described. The electrical fusion process consists of two steps: the cells are collected to form pearl-chains between Pt electrodes by the action of dielectrophoresis, then a brief DC pulse is applied, such that the breakdown voltage of the membranes is briefly exceeded and cell-to-cell juncture of the membranes occurs around the pore formed by the pulse. Giant fused cells (diameter up to 100 m) can be formed by the electrically mediated fusion of mouse 3T3 fibroblast cells, provided that pronase is added just before field application.     

Mechanical stabilization of guard cell protoplasts of Vicia faba

Guard cell protoplasts of Vicia faba were immobilized in cross-linked Ca-alginate. No visible morphological changes were detected under the light microscope over a period of 14 days. The entrapped cells reacted normally to changes of the external osmolarity by shrinking and swelling. Addition of the calcium complexing agent, citrate, led to dissolution of the matrix. After reequilibration with Ca ions the released cells regained their ability to swell and shrink in response to external stress. The released protoplasts could be stained with the vital dye, neutral which was accumulated in the vacuoles. It should also be noted that the protoplasts can be transported when immobilized.