Regional specialization of retinal glial cell membrane

Neural activity generates increases in extracellular K+ concentration, [K+]0, which must be regulated in order to maintain normal brain function. Glial cells are thought to play an important part in this regulation through the process of K+ spatial buffering: K+-mediated current flow through glial cells redistributes extracellular K+ following localized [K+]0 increases. As is the case in other glia, the retinal Müller cell is permeable almost exclusively to K+ . Recent experiments have suggested that this K+ conductance may not be distributed uniformly over the cell surface. In the present study, two novel techniques have been used to assess the Müller cell K+ conductance distribution. The results demonstrate that 94% of all membrane conductance lies in the endfoot process of the cell. This strikingly asymmetric distribution has important consequences for theories concerning K+ buffering and should help to explain the generation of the electroretinogram.     

The effects of secretin on urinary volume and electrolytes in normal subjects and patients with chronic pancreatic disease

Zusammenfassung Injektion von Sekretin ruft bei normalen Versuchspersonen Diuresis und Vermehrung der Natrium- und Alkali-Ausscheidung hervor. Diese Wirkungen sind vermindert bei Patienten mit chronischer Pankreaserkrankung. Der mögliche Mechanismus und die praktische Bedeutung dieser Beobachtungen werden diskutiert.

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Supported successively by grants from the Royal Free Hospital Endowment Fund.     

Voltage-dependent calcium and potassium channels in retinal glial cells

Glial cells, which outnumber neurones in the central nervous system, have traditionally been considered to be electrically inexcitable and to play only a passive role in the electrical activity of the brain. Recent reports have demonstrated, however, that certain glial cells, when maintained in primary culture, possess voltage-dependent ion channels. It remains to be demonstrated whether these channels are also present in glial cells in vivo. I show here that Müller cells, the principal glial cells of the vertebrate retina, can generate 'Ca2+ spikes' in freshly excised slices of retinal tissue. In addition, voltage-clamp studies of enzymatically dissociated Müller cells demonstrate the presence of four types of voltage-dependent ion channels: a Ca2+ channel, a Ca2+-activated K+ channel, a fast-inactivating (type A) K+ channel and an inward-rectifying K+ channel. Currents generated by these voltage-dependent channels may enhance the ability of Müller cells to regulate extracellular K+ levels in the retina and may be involved in the generation of the electroretinogram.     

Single-copy insertion of transgenes in Caenorhabditis elegans

At present, transgenes in Caenorhabditis elegans are generated by injecting DNA into the germline. The DNA assembles into a semistable extrachromosomal array composed of many copies of injected DNA. These transgenes are typically overexpressed in somatic cells and silenced in the germline. We have developed a method that inserts a single copy of a transgene into a defined site. Mobilization of a Mos1 transposon generates a double-strand break in noncoding DNA. The break is repaired by copying DNA from an extrachromosomal template into the chromosomal site. Homozygous single-copy insertions can be obtained in less than 2 weeks by injecting approximately 20 worms. We have successfully inserted transgenes as long as 9 kb and verified that single copies are inserted at the targeted site. Single-copy transgenes are expressed at endogenous levels and can be expressed in the female and male germlines.     

A role for excreted quinones in extracellular electron transfer

Respiratory processes in bacteria are remarkable because of their ability to use a variety of compounds, including insoluble minerals, as terminal electron acceptors. Although much is known about microbial electron transport to soluble electron acceptors, little is understood about electron transport to insoluble compounds such as ferric oxides. In anaerobic environments, humic substances can serve as electron acceptors and also as electron shuttles to ferric oxides. To explore this process, we identified mutants in Shewanella putrefaciens that are unable to respire on humic substances. Here we show that these mutants contain disruptions in a gene that is involved in the biosynthesis of menaquinone. During growth, the wild type releases a menaquinone-related redox-active small molecule into the medium that complements the mutants. This finding raises the possibility that electron transfer to a variety of oxidants, including poorly soluble minerals, may be mediated by microbially excreted quinones that have yet to be identified.