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⁺](o) increases. The measured magnitude of stimulation induced [K⁺](o) 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⁺]o 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⁺]o 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 standardise the tip sizes of the ISMs used in their experiments.