Construction of K+- and Na+-sensitive theta-microelectrodes with fine tips: an easy method with high yield.

A new method is described to prepare theta-microelectrodes with tips up to 0.15 micron diameter controlled under scanning electron microscope. K+- and Na+-sensitive resins were tested. Method features are the following: i) hard drying of the glass, ii) rehydration of one channel and weak wetting of the other with a three-methylchlorosilane solution before pulling, iii) simultaneous presence of water and silane in the two channels during pulling, iv) gradual silanization from the tip to the shank. Selective and conventional channels did not affect each other and no displacements of resins were observed. The change of potential difference of the selective channel was more than -50 mV/decade. Apical membrane potentials and cell Na+ and K+ activities of the epithelial cells of rabbit gall-bladder (cell diameter: 5-10 micron) were measured with these theta-microelectrodes and with single-barrel microelectrodes of similar tip size: results obtained were not significantly different.