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PubMed1999

Microelectrode measurements of the effects of basolateral adenosine in polarized human intestinal epithelial cells in culture.

Activation of the basolateral receptor for adenosine in HT-29cl.19A cells, by 100 microM adenosine, increased the equivalent short-circuit current (DeltaIsc= 24+/-2 microA/cm2), depolarized the intracellular potential (DeltaVa= 26+/-2 mV) and decreased the fractional apical membrane resistance (DeltafRa=-0.48). The changes in all parameters reached their peak values simultaneously. This suggests that the primary action of the adenosine-activated pathway is on only one membrane. Bumetanide inhibited the transepithelial response and repolarized the cell potential. After preincubation with 100 microM forskolin, application of 300 microM adenosine caused a significant further change in Va, Isc, the transepithelial potential (Vt) and fRa. Together with the results from ion-replacement studies, the observations indicate that adenosine activates channels other than the cystic fibrosis transmembrane conductance regulator (CFTR). The rank order of potencies of adenosine and adenosine analogues implies that the receptor is of the A2 subtype. Preincubation with 4-bromophenacyl bromide (4-BPB) inhibited the effect of an adenosine analogue by 50%, indicating that activation of phospholipase A2 may be involved in the adenosine-induced response.

Acetophenones↗
PubMed2000

A polarographic, oxygen-selective, vibrating-microelectrode system for the spatial and temporal characterisation of transmembrane oxygen fluxes in plants.

A simple procedure is described for the fabrication of micrometer to nanometer-scale platinum electrodes to be used in a vibrating oxygen-selective system. The electrode was prepared by etching a fine platinum wire and insulating it with an electrophoretic paint. The dimensions allowed this electrode to be used with the "vibrating probe technique" in exploratory studies aimed at mapping and measuring the patterns of net influxes as well as effluxes of oxygen in Olea europaea L. leaves and roots with spatial and temporal resolutions of a few microns and a few seconds, respectively. The magnitude and spatial localisation of O2 influxes in roots was characterised by two distinct peaks. The first, in the division zone, averaged 38 +/- 5 nmol m(-2) s(-1); the second, in the elongation region, averaged 68 +/- 6 nmol m(-2) s(-1). Long-term records of oxygen influx in the elongation region of the root showed an oscillatory regime characterised by a fast oscillation with periods of about 8-9 min. In leaves, the system allowed the measurement of real-time changes in O2 evolution following changes in light. Furthermore, it was possible to obtain "topographical" images of the photosynthetically generated oxygen diffusing through different stomata from a region of the leaf of 120 microm x 120 microm. The combination of topographic and electrochemical information at the micrometer scale makes the system an efficient tool for studying biological phenomena involving oxygen diffusion.

Kinetics↗