Procedures for manufacturing double-barrelled ion-sensitive microelectrodes employing liquid sensors

Sensitivity of valinomycin-based K(+)-selective micro-electrodes to inhibitors of K+ transport

The sensitivies of double-barrelled K(+)-selective micro-electrodes (KSMs) employing the low-impedance membrane cocktail based on the neutral K(+)-selective ion carrier valinomycin (Fluka, Cocktail B 60398) to the following 3 different classes of inhibitors of K+ transport were measured: (1) general metabolic inhibitors (dinitrophenol, potassium cyanide, sodium azide, rotenone, dicyclohexylcarbodiimide, salicylhydroxamic acid); (2) P-type ATPase inhibitors (vanadate, ouabain, amiloride, SCH 28080); and (3) anion-dependent K+ transport inhibitors (bumetanide, 4-acetamide-4-isothiocyanostilbene-2,2-disulphonic acid). Of the 12 inhibitors tested, only dinitrophenol had any significant effect on the response of KSMs to K+ activity. Comparison of the calibrations in solutions with and without 0.1 mM dinitrophenol showed that this inhibitor behaved as a 'classical' interferent whereby its contribution to the K+ activity signal was statistically significant at K+ activities of 36.0 mM and less. However, at higher K+ activities (97.0 mM), dinitrophenol interference was not significant. It was possible to correct for the DNP interference and to obtain measurements of intracellular K+ activity in insect muscles.

An ion-sensitive microelectrode study on the effect of a high concentration of ivermectin on chloride balance in the somatic muscle bag cells of Ascaris suum

Ivermectin has been shown to increase chloride conductances of invertebrate cells. On the muscle cells of the parasitic nematode Ascaris, ivermectin acts as both a GABA receptor antagonist and a chloride channel opener. In this study, ion-sensitive microelectrodes were used to investigate the effect of ivermectin on intracellular Cl- concentration of the somatic muscle bag cells of Ascaris suum. Incubation of muscle cells with ivermectin (10 microM in 1% dimethyl sulphoxide vehicle for 60 min) increased intracellular Cl- by 2.9 mM or 15% compared to controls (P < 0.01, n = 6).

Ion-selective microelectrodes suitable for recording rapid changes in extracellular ion concentration

A method for fabricating double-barrel, ion-selective microelectrodes with fine tips (0.5-1.5 microns) and rapid response times is described. When made into K(+)-selective microelectrodes, the electrodes respond to changes in [K+]o with a time constant of 70-95 ms. The electrical response of these electrodes to common-mode voltages can be made to have a time constant of less than 2 ms, which minimizes electrical artifacts from field potentials. The application of these microelectrodes to the measurement of rapid, transient changes in retinal [K+]o is presented.

A method for the manufacture of single barrel liquid ion-selective microelectrodes: an in situ study of ant venom pH

A method for the manufacture of single barrel ion-sensitive microelectrodes, employing liquid ion-selective sensors, is described in detail. This method had proven reliable and repeatable for the manufacture of pH-sensitive microelectrodes using a liquid proton carrier. It is believed that this method has advantages over other published methods since it allows direct visualization and control of major steps during electrode fabrication and overcomes several problems often encountered using more conventional methods. Microelectrodes fabricated using this technique have been used to measure the in situ pH of venom from two myrmicine ants, Tetramorium caespitum (L.) and Myrmica ruginodis (N.).

Micro-electrode measurements and functional aspects of chloride activity in cyprinid fish retina: extracellular activity and intracellular activities of L- and C-type horizontal cells

Extracellular Cl- activity and intracellular Cl- activities of luminosity and biphasic-chromaticity type horizontal cells were measured in freshly isolated, non-superfused roach retinae using double-barrelled Cl- -sensitive micro-electrodes. The extracellular Cl- activity in dark-adapted retinae was found to have a surprisingly wide range (54-143 mM), although in a given preparation it was extremely constant. The mean intracellular Cl- activities of both types of horizontal cell were identical (47 mM), and this value was significantly greater than that required for "passive distribution" i.e. Cl- equilibrium potentials were 11-12 mV more positive than respective membrane resting potentials in the dark. In the presence of 10 microM dopamine, however, the difference between the Cl- equilibrium potential and the membrane resting potential was abolished, consistent with the hypothesis that dopamine increases Cl- conductance, presumably at the interplexiform cell synapse onto horizontal cells. In turn, it is suggested that a functional consequence of this pathway is to modulate the input impedances of the horizontal cells, and hence their sensitivity to light.

Intracellular potassium activities of horizontal cells and extracellular potassium activity in isolated retinae of a cyprinid fish

Extracellular and intracellular K+ activities of luminosity and biphasic-chromaticity type horizontal cells were measured in non-superfused roach retinae using double-barrelled K+-sensitive micro-electrodes. The extracellular K+ activity in dark-adapted retinae was 3.4 mM on average. The intracellular K+ activities of the two types of horizontal cell in the dark were very similar (57 and 54 mM, respectively), and corresponding values of the K+ equilibrium potential were about 35 mV more negative than respective resting potentials. During light-evoked hyperpolarizations, the intracellular K+ activity decreased, and at saturation, resting potentials matched corresponding K+ equilibrium potentials. The results are discussed in relation to sub-synaptic and non-synaptic membrane ionic mechanisms and further support the view that the non-synaptic membrane is selectively permeable to K+.