Effects of aging on potassium homeostasis and the endocochlear potential in the gerbil cochlea

• Published in: Hearing research 1996-12, Vol.102 (1), p.125-132
• Main Author: Schmiedt, Richard A.
• Format: Article
• Language: English
• Subjects: Acoustic Stimulation; Aging; Aging - pathology; Animals; Biological and medical sciences; Calibration; Cochlea; Cochlear Microphonic Potentials - physiology; Disease Models, Animal; Ear and associated structures. Auditory pathways and centers. Hearing. Vocal organ. Phonation. Sound production. Echolocation; Electrodes, Implanted; Endocochlear potential; Endolymph; Endolymph - metabolism; Endolymph - physiology; Fundamental and applied biological sciences. Psychology; Gerbil; Gerbillinae; Homeostasis - drug effects; Meriones unguiculatus; Microelectrodes; Perilymph; Perilymph - metabolism; Perilymph - physiology; Potassium; Potassium - metabolism; Presbyacusis; Presbycusis - diagnosis; Presbycusis - etiology; Sodium-Potassium-Exchanging ATPase - metabolism; Stria Vascularis - enzymology; Tympanic Membrane - physiology; Vertebrates: nervous system and sense organs
• ISSN: 0378-5955; 1878-5891
• DOI: 10.1016/S0378-5955(96)00154-2

Previous work has shown that the endocochlear potential (EP) decreases with age in the gerbil. Concomitant with the EP decrease is an age-related loss of activity of Na,K-ATPase in the lateral wall and stria vascularis. We hypothesized that the EP decrease is associated with a similar decrease in the endolymphatic potassium concentration [K e +]. This hypothesis was tested using double-barrelled, K +-selective electrodes introduced into scala media through the round window in young and quiet-aged gerbils. Results show that the means (±S.D.) of the [K e +] in young and aged gerbils were not significantly different (178.2 ± 14.2 mM and 171.2 ± 34.4 mM, respectively), although the intersubject variability was much greater in the aged animals than in the young. These values of [K e +] are slightly higher than those found for other mammals and may reflect the higher plasma osmolarity found in the gerbil. The concentration of perilymphatic potassium [K p +] in scala tympani at the round window was also similar for the young and aged groups (3.57 ± 1.17 mM and 4.18 ± 2.03 mM, respectively). On the other hand, mean EP values in the young and aged gerbils were 92.0 ± 5.7 mV and 64.8 ± 15.8 mV, respectively and were statistically different ( P < 0.001). Overall, EP and [K e +] showed little correlation ( R 2 = 0.23), except that when [K e +] fell below 150 mM, the EP was always less than 60 mV. An analysis of the chemical potential for K e + with respect to K p + shows that it was similar for young and aged gerbils (overall mean of 103.1 ± 13.7 mV) and remained constant with respect to the EP, in spite of an overall electrochemical potential of K e + that varied from 120 to 210 mV. Thus, the system maintains K e + homeostasis at the expense of the EP, even when the EP is on the verge of collapse.