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At least 433 records · Page 24Linked to original sources
PubMed1985

Extracellular K+ activity changes related to electroretinogram components. I. Amphibian (I-type) retinas.

Electroretinographic (ERG) and extracellular potassium activity measurements were carried out in superfused eyecup preparations of several amphibians. Light-evoked changes in extracellular K+ activity were characterized on the bases of depth profile analysis and latency measurements and through the application of pharmacological agents that have selective actions on the retinal network. Three different extracellular potassium modulations evoked at light onset were identified and characterized according to their phenomenological and pharmacological properties. These modulations include two separable sources of light-evoked increases in extracellular K+: (a) a proximal source that is largely post-bipolar in origin, and (b) a distal source that is primarily or exclusively of depolarizing bipolar cell origin. The pharmacological properties of the distal extracellular potassium increase closely parallel those of the b-wave. A distal light-evoked decrease in extracellular potassium appears to be associated with the slow PIII potential, based on a combination of simultaneous intracellular Müller cell recordings and extracellular ERG and potassium activity measurements before and during pharmacological isolation of the photoreceptor responses. The extracellular potassium activity increases are discussed with respect to the Müller cell theory of b-wave generation.

Ambystoma↗
PubMed1989

Determination of murein precursors during the cell cycle of Escherichia coli.

A convenient and reliable method has been established that allows a quantitative determination of m-diamino[3H]pimelic acid-labelled murein precursors in 1 ml culture samples of Escherichia coli. Prior to separation by reversed-phase high-pressure liquid chromatography the lipid-linked intermediates were hydrolysed to release the muropeptides. The accuracy for the measurement of UDP-N-acetylmuramylpentapeptide (UDP-MurNAc-pentapeptide) was +/- 1.9% (SD), for undecaprenyl-P-P-MurNAc-pentapeptide (lipid I) +/- 10% (SD) and for undecaprenyl-P-P-(GlcNAc-beta 1----4)MurNAc-pentapeptide (lipid II) +/- 5% (SD). The ratio of UDP-MurNAc-pentapeptide:lipid I:lipid II was about 300:1:3 for E. coli MC4100. The relative cellular concentrations of all three precursor molecules were found not to vary throughout the cell cycle. It is concluded that elongation and division of the murein sacculus is not controlled by oscillations in the concentrations of these late murein precursors.

Cell Cycle↗
PubMed1975

Sphere-rod morphogenesis of Escherichia coli.

The morphogenetic capacity of E. coli was studied by converting the rod-shaped cells into spheres and then determining whether these spheres could revert to rods. The morphogenesis of cells was followed by immobilizing them in a viscous Methocel-containing medium. Two different types of spheres were prepared: cells which retained a mechanically intact sacculus, and osmotically sensitive sphaeroplasts lacking a sacculus. The sphaeroplasts were not able to revert to rods although they were able to synthesize a new sacculus. In contrast, spheres which had retained an intact sacculus were able to reshape themselves into rods. The were also able to form new ends at (or near) the sites of the ends on the original rods.

Cell Wall↗