Tip size of ion-exchanger based K+-selective microelectrodes. II. Effects on measurement of evoked [K+]0 transients.

Double-barreled ion-exchanger based K+-selective microelectrodes (K+ ISMs) of a variety of tip diameters were used to provide an experimental test of predictions that microelectrode tip induced tissue damage influences the magnitude of measured [K+]0 increases. The measured magnitude of stimulation induced [K+]0 rises in the rat optic nerve depended on the tip diameter of the measuring K+ ISM; smaller tipped K+ ISMs tended to measure larger rises of [K+]0 than bigger tipped K+ ISMs. When stimulated [K+]0 increases were simultaneously recorded with 2 K+ ISMs of different tip size, the smaller tipped K+ ISM recorded [K+]0 increases that were, on average, 14% larger than the increases measured by the bigger tipped K+ ISM. In view of these results, and those presented in the previous paper, investigators should standardize the tip sizes of the ISMs used in their experiments.