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[Ion-selective microelectrodes: principle and application of in vivo measurements of ionic concentrations in cochlear
Objective:
To introduce the method of making neutral carrier ion-selective microelectrode and use it for in vivo measurement of ionic concentrations in cochloear endolymph.
Methods:
GG-17 glass capillaries with 1.85 mm O.D. were rinsed extensively and dried in an oven. Two capillaries were parallelly connected and pulled with microelectrode puller to make a double-barreled micropipette. One barrel was back-filled with ion exchanger and internal reference solution, which served as ionic potential electrode, while the other barrel filled with 150 mmol/L KCL as reference electrode. Each barrel of microelectrode was connected to differential electrometer via Ag-AgCl wire and output was recorded on a three-channel recorder. Every ion-selective microelectrode was calibrated in a series of standard solutions to determine the required characteristics. Twenty healthy guinea pigs with normal hearing were anesthetized and were artificially respired through the tracheal canal after the intramuscular injection of suxamethonium chloride. The tympanic bulla was exposed and a double-barreled ion-selective electrode was inserted into the scala media through the round window and basilar membrane. The ionic potentials and endocochlear potentials (EP) were simultaneously recorded from the basal turn of the cochlea. Ionic concentrations were then calculated by Nicolsky-Eisenman equation.
Results:
The concentrations of potassium, sodium and calcium ions in the cochlear endolymph were 146.3 +/- 11.8 mmol/L, 0.36 +/- 0.22 mmol/L and 16.2 +/- 5.7 micromol/L, respectively.
Conclusions:
The neutral carrier ion-selective microelectrode made with the above method is reliable and therefore can be used for accurately measuring the ionic concentrations of microenvironment in vivo continuously and transiently.