Effects of CO2/HCO3− in Perilymph on the Endocochlear Potential in Guinea Pigs

• Published in: Journal of Physiological Sciences Vol. 57; no. 1; pp. 15 - 22
• Main Authors: Nimura, Yoshitsugu, Mori, Yoshiaki, Inui, Takaki, Sohma, Yoshiro, Takenaka, Hiroshi, Kubota, Takahiro
• Format: Journal Article
• Language: English; Japanese
• Published: Japan PHYSIOLOGICAL SOCIETY OF JAPAN 01.01.2007; The Physiological Society of Japan; BioMed Central
• Subjects: Ammonium Chloride - metabolism; Animals; asphyxia; Asphyxia - metabolism; Bicarbonates - metabolism; Calcium - metabolism; Calcium Channel Blockers - pharmacology; carbon dioxide; Carbon Dioxide - metabolism; Cochlea - drug effects; Cochlea - metabolism; endocochlear potential; Endolymph - drug effects; Endolymph - metabolism; Guinea Pigs; Hydrogen-Ion Concentration; intracellular Ca2; Ion-Selective Electrodes; Membrane Potentials; Microelectrodes; nifedipine; Nifedipine - pharmacology; Perfusion; Perilymph - drug effects; Perilymph - metabolism; Time Factors
• ISSN: 1880-6546; 1880-6562
• DOI: 10.2170/physiolsci.RP012006

The effect of CO2/HCO3− on the endocochlear potential (EP) was examined by using both ion-selective and conventional microelectrodes and the endolymphatic or perilymphatic perfusion technique. The main findings were as follows: (i) A decrease in the EP from ∼+75 to ∼+35 mV was produced by perilymphatic perfusion with CO2/HCO3−-free solution, which decrease was accompanied by an increase in the endolymphatic pH (ΔpHe, ∼0.4). (ii) Perilymphatic perfusion with a solution containing 20 mM NH4Cl produced a decrease in the EP (ΔEP, ∼20 mV) with an increase in the pHe (ΔpHe, ∼0.2), whereas switching the perfusion solution from the NH4Cl solution to a 5% CO2/25 mM HCO3− solution produced a gradual increase in the EP to the control level with the concomitant recovery of the pHe. (iii) The perfusion with a solution of high or low HCO3− with a constant CO2 level within 10 min produced no significant changes in the EP. (iv) Perfusion of the perilymph with 10 \\xb5 g/ml nifedipine suppressed the transient asphyxia-induced decrease in EP slightly, but not significantly. (v) By contrast, the administration of 1 μg/ml nifedipine via the endolymph inhibited significantly the reduction in the EP induced by transient asphyxia or perilymphatic perfusion with CO2/HCO3−-free or 20 mM NH4Cl solution. These findings suggest that the effect of CO2 removal from perilymphatic perfusion solution on the EP may be mediated by an increase in cytosolic Ca2+ concentration induced by an elevation of cytosolic pH in endolymphatic surface cells.