title: Effects of aging on potassium homeostasis and the endocochlear potential in the gerbil cochlea.
abstract: 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 [Ke+]. 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 [Ke+] 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 [Ke+] 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 [Kp+] 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 [Ke+] showed little correlation (R2 = 0.23), except that when [Ke+] fell below 150 mM, the EP was always less than 60 mV. An analysis of the chemical potential for Ke+ with respect to Kp+ 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 Ke+ that varied from 120 to 210 mV. Thus, the system maintains Ke+ homeostasis at the expense of the EP, even when the EP is on the verge of collapse.
authors.affiliation: Department of Otolaryngology and Communicative Sciences, Medical University of South Carolina, Charleston 29425-2242, USA. schmiera@musc.edu
authors.forename: R A
authors.initials: RA
authors.lastname: Schmiedt
mesh_terms: D000161:Acoustic Stimulation; D000375:Aging / Q000473:pathology*; D000818:Animals; D002138:Calibration; D003055:Cochlear Microphonic Potentials / Q000502:physiology*; D004195:Disease Models, Animal; D004567:Electrodes, Implanted; D004710:Endolymph / Q000378:metabolism / Q000502:physiology; D005849:Gerbillinae; D006706:Homeostasis / Q000187:drug effects; D008839:Microelectrodes; D010498:Perilymph / Q000378:metabolism / Q000502:physiology; D011188:Potassium / Q000378:metabolism*; D011304:Presbycusis / Q000175:diagnosis / Q000209:etiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013316:Stria Vascularis / Q000201:enzymology; D014432:Tympanic Membrane / Q000502:physiology
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium