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M Cannell

Publications and source records attributed to M Cannell.

6 recordsLinked to original sources
PubMed2001

Procedures allowing the transformation of a range of European elite wheat (Triticum aestivum L.) varieties via particle bombardment.

Ten current European wheat varieties were transformed at efficiencies ranging from 1-17% (mean 4% across varieties) following modifications in particle bombardment and tissue culture procedures. All plants surviving phosphinothricin selection were screened for uidA and bar gene activity, and for the presence of marker gene sequences by PCR analysis. A minimum of 35% plant 'escape' frequency was achieved with selection on 4 mg l(-1) gluphosinate ammonium after shoot initiation. Mean co-transformation frequency with various genes-of-interest was 66%. The estimated number of insertions of the uidA gene in 25 lines were; 1-2 in 32%, 3-5 in 52%, and 6-8 in 16% of lines. In T(1) progenies, marker genes segregated in a Mendelian fashion in 50% of 39 lines analysed, as determined by transgene activity assays. Based on PCR analysis, it appeared that in some lines the occurrence of distorted segregation was due to poor transmission of the transgenes.

Base Sequence↗
PubMed1992

Calcium entry-dependent oscillations of cytoplasmic calcium concentration in cultured endothelial cell monolayers.

Bovine endothelial cell monolayers grown to confluence and stimulated with bradykinin responded with periodic fluctuations in intracellular Ca2+ concentration ([Ca2+]i) when exposed to K(+)-free Hepes-buffered saline. The fluctuations in [Ca2+]i measured with fura-2 were synchronized among the population of cells observed and were sensitive to extracellular Ca2+ concentration ([Ca2+]o). Thapsigargin, which inhibits the endoplasmic reticular Ca2(+)-ATPase, did not inhibit the [Ca2+]i oscillations. Removal of extracellular Ca2+ or inhibition of Ca2+ entry by using La3+ or 1-(beta- [3-(4-methoxyphenyl)proproxy]-4-methoxyphenethyl)-1H-imidazole hydrochloride (SKF 96365) abolished the [Ca2+]i oscillations in endothelial cell monolayers. The fluctuations in [Ca2+]i were therefore dependent on Ca2+ influx rather than Ca2+ mobilization from intracellular stores. Simultaneous measurements of membrane potential (Em) using the potential-sensitive bisoxonol dye bis(1,3-dibutylbarbituric acid)trimethine oxonol [Di-BAC4(3)] and [Ca2+]i using fura-2 showed that Em oscillated at the same frequency as the fluctuations in [Ca2+]i. The peak depolarization signal coincided with the maximum rate of increase in the [Ca2+]i signal. Oscillations in the Em signal were inhibited by removal of Ca2+ or by addition of 1 mM Ni2+ to the external solution. Taken together, these observations suggest that the change in Em is the consequence of oscillatory changes in a membrane conductance that also allows Ca2+ to enter the cell. Oscillations in the DiBAC4(3) signal may reflect a rhythmic entry of Ca2+ through nonselective cation channels.

Animals↗
PubMed1992

The superficial buffer barrier in vascular smooth muscle.

Force development and fura-2 fluorescence were simultaneously measured in the rabbit inferior vena cava. Discharging SR Ca2+ with either caffeine or norepinephrine prior to stimulation of Ca2+ influx induced a delay of 30-70 s between the intracellular Ca2+ signal and development of force. This delay was abolished by the application of caffeine. These data support the superficial buffer barrier hypothesis, which holds that Ca2+ entry from the extracellular space proceeds via a restricted cytoplasmic region between the inner plasmalemmal surface and the peripheral sarcoplasmic reticulum (SR). Ca2+ accumulation by this SR fraction appears to be able to delay Ca2+ entry into the deeper myoplasm where it activates the myofilaments. Caffeine and thapsigargin elevated the steady-state [Ca2+]i, suggesting a contribution by the SR Ca2+ pump to Ca2+ extrusion from the cells. Norepinephrine enhanced myofilament Ca2+ sensitivity, while caffeine decreased it.

Animals↗
PubMed1982

The dependence on heart rate of the human ventricular action potential duration.

For the human electrocardiogram, the relationship between QT interval and heart rate was examined in conditions where the heart rate was changed at different rates. The QT interval provides a measure of the ventricular action potential duration. For slow changes of heart rate, elicited by mild exercise, the dependence of QT interval on heart rate obtained when the heart rate was rising was the same as that obtained when the heart rate was falling. The QT interval was approximately proportional to 1/(heart rate)1/2. For the rapid transient changes of heart rate associated with respiration, the QT interval was approximately constant, independent of the instantaneous heart rate. For rapid sustained changes of heart rate, elicited by heavy exercise or immersion of the face in cold water, the changes in QT interval lagged behind the heart rate changes. Consequently the dependence of QT interval on heart rate obtained when the heart rate was increasing differed from the dependence obtained during a fall in heart rate. This time dependence of the relationship between QT interval and heart rate is similar to that seen for the relationship between action potential duration and stimulation rate in isolated pieces of mammalian ventricle.

Action Potentials↗