Calcium transport mechanism in the endolymph of the chinchilla.
The Ca2+ transport mechanism between endolymph and perilymph was evaluated by the effects of vanadate and amiloride on the endocochlear potential (EP) and the Ca2+ concentration in endolymph using Ca2+-selective microelectrodes. Under normal conditions, the EP was 81.8 +/- 0.9 mV, and the Ca2+ concentrations in endolymph and perilymph were 16.6 +/- 1.3 microM and 1.85 +/- 0.11 mM (N = 12), respectively. Therefore, the uphill electrochemical potential gradient for Ca2+ from perilymph to endolymph, 20.2 +/- 2.0 mV, indicates the existence of an active uptake of Ca2+ into endolymph. Vanadate, the inhibitor of Ca2+-ATPase, topically applied to the round window membrane caused biphasic changes of the EP and the endolymph Ca2+ concentration; the former in a transient increase followed by a consistent decrease and the latter in a slow decrease followed by a slow increase. Amiloride induced a slight EP depression and a concomitantly slight elevation of the Ca2+ concentration in endolymph. The electrochemical potential gradient for Ca2+ between endolymph and perilymph vanished with the use of vanadate but was not affected by amiloride. These results suggest that Ca2+-ATPase, sensitive to vanadate, maintained the bulk of active Ca2+ transport in the cochlea and that the participation of Na+-Ca2+ exchange is negligible.
Ikeda
K
K
Department of Otolaryngology, University of Minnesota, Minneapolis 55414.
Morizono
T
T
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000493:pharmacokinetics*; D000252:Calcium-Transporting ATPases / Q000502:physiology; D002682:Chinchilla; D003055:Cochlear Microphonic Potentials / Q000187:drug effects; D004710:Endolymph / Q000502:physiology*; D007761:Labyrinthine Fluids / Q000502:physiology*; D010498:Perilymph / Q000502:physiology; D014638:Vanadates / Q000494:pharmacology*
D014638:Vanadates; D000584:Amiloride; D000252:Calcium-Transporting ATPases; D002118:Calcium