Abstract
Feldman and Brusilow [Proc. Natl. Acad. Sci. USA 73, 1761 (1976)] reported that endolymphatic injection of cholera toxin (adenylate cyclase stimulator) results in endolymphatic hydrops, the pathological substrate of Meniere's disease. The authors postulated that the situation is similar to the intestine, where the cholera toxin mediated elevation of cAMP levels causes profuse fluid secretion. We found that perilymphatic application of cholera toxin caused an approximately 2× increase of cAMP in Reissner's membrane (RM), but no significant changes in stria vascularis (SV) and organ of Corti (OC). Endolymphatic perfusion produced no changes. However, when cholera toxin, in combination with theophylline (phosphodiesterase inhibitor) was perfused perilymphatically, a dramatic increase in cAMP levels occurred in RM (80×), a substantial increase in OC (8×), but only a small increase in SV (2×). Endolymphatic perfusion caused a 20×, 4×, and 3.5× increase, respectively. These results indicate that RM may be more important in cochlear fluid homeostasis than generally assumed. Note, however, that the relatively low level of strial cAMP may be due to clearance via the vasculature. [Supported by NIH.]
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