ADENYLATE-CYCLASE MODULATION OF ION PERMEABILITY IN THE GUINEA-PIG COCHLEA - A POSSIBLE MECHANISM FOR THE FORMATION OF ENDOLYMPHATIC HYDROPS

The pathophysiological mechanisms leading to endolymphatic hydrops in Meniere's disease are unknown. Changes in ionic permeability of the cellular membranes between the endolymph and the perilymph, which after the composition and osmolarity of the inner ear fluid, may be a major factor in the etiology of endolymphatic hydrops. To determine the possible involvement of adenylate cyclase in the formation of endolymphatic hydrops, we measured the endolymphatic K+, Na+, Cl- activities (A(K), A(Na), A(Cl)) and the endocochlear potential (EP) by means of ionselective microelectrodes while inner ear adenylate cyclase was activated by perilymphatic perfusion with forskolin. We observed a large A(Cl) increase accompanied by an EP increase during forskolin (2 x 10(-4) M) perfusion and a delayed A(K) decrease after perfusion. No measurable A(Na) change was observed. These results suggest that adenylate cyclase may regulate Cl-permeability of the endolymph-perilymph barrier and that adenylate cyclase plays a critical role in acute endolymphatic hydrops in Meniere's disease by altering the osmolarity of the endolymph.