Fabrication and Use of High-Speed, Concentric H⁺- and Ca²⁺-Selective Microelectrodes Suitable for In Vitro Extracellular Recording

Abstract

Ion-selective microelectrodes (ISMs) have been used extensively in neurophysiological studies. ISMs selective for H(+) and Ca(2+) are notable for their sensitivity and selectivity, but suffer from a slow response time, and susceptibility to noise because of the high electrical resistance of the respective ion exchange cocktails. These drawbacks can be overcome by using a "coaxial" or "concentric" inner micropipette to shunt the bulk of the ion exchanger resistance. This approach was used decades ago to record extracellular [Ca(2+)] transients in cat cortex, but has not been subsequently used. Here, we describe a method for the rapid fabrication of concentric pH- and Ca(2+)-selective microelectrodes useful for extracellular studies in brain slices or other work in vitro. Construction was simplified compared with previous implementations, by using commercially available, thin-walled borosilicate glass, drawing an outer barrel with a rapid taper (similar to a patch pipette), and by use of a quick and reliable silanization procedure. Using a piezoelectric stepper to effect a rapid solution change, the response time constants of the concentric pH and Ca(2+)-electrodes were 14.9 +/- 1.3 and 5.3 +/- 0.90 ms, respectively. Use of these concentric ISMs is demonstrated in rat hippocampal slices. Activity-dependent, extracellular pH, and [Ca(2+)] transients are shown to arise two- to threefold faster, and attain amplitudes two- to fourfold greater, when recorded by concentric versus conventional ISMs. The advantage of concentric ISMs for studies of ion transport and ion diffusion is discussed.

Double-barreled and Concentric Microelectrodes for Measurement of Extracellular Ion Signals in Brain Tissue

“…As expected 21 , application of glutamate (10 mM Thus, these results demonstrate and confirm the faster response kinetics of concentric vs. double-barreled Na + -selective microelectrodes, (cf. Figure 6C and 8B), as was also noted for Ca 2+ and pH-selective counterparts 10 . In contrast to the former study, in which short-burst synaptic stimulation was performed to evoke fast synaptically-induced ion transients, there was only a tendency, but no significant difference in mean peak amplitudes between concentric and double-barreled electrodes with our application paradigm.…”

“…In addition to the classical double-barreled electrodes, so-called concentric electrodes were recently introduced. The latter provide a superior time resolution, but take a little more time and effort to construct 10 .…”

Protons are a neurotransmitter that regulates synaptic plasticity in the lateral amygdala

“…Several processes may restore and increase pH, including proton diffusion, pH buffering, and activity of membrane transporters (11). Increased interstitial pH after neurostimulation has also been reported in other preparations (11,42,47). Previous studies showed that raising extracellular pH before an acid stimulus reduced steady-state inactivation and increased the amplitude of ASIC currents (43,44,48).…”

Sequential pH-driven dimerization and stabilization of the N-terminal domain enables rapid spider silk formation

“…In addition, spidroins are subjected to a pH drop from B7 in the middle region of the storage sac to 6.3 in the duct 9,10 . Recently, we used concentric ion selective microelectrodes 11 to measure a pH B5.7 halfway through the major ampullate duct, and the pH likely reaches even lower levels in the distal part of the duct (MA et al, unpublished work).…”