[Measurement of Ca2+ concentration and endocochlear potential in experimental endolymphatic hydrops in vivo]

This study was based on observations on 14 normal guinea pigs and 17 guinea pigs in which the left endolymphatic duct and sac had been surgically obliterated to induce endolymphatic hydrops. Three groups of hydropic animals were tested 1, 2 and 3 months after surgery. The Ca2+ concentration and endocochlear potential (EP) were recorded by means of double-barrelled ion selective micro-electrode in the third turn of the cochlea. The results indicated that a decrease in EP and an increase in Ca2+ in hydropic cochlea, a negative correlation was present. In the control ear, the values of Ca2+ and EP were 26.4 +/- 0.33 microns/L (n = 14) and 72.78 mV (n = 14), respectively; in the hydropic ear, the value of Ca/+ was 404.47 +/- 79.74 microns/L (n = 17), while the EP was 55.82 +/- 3.28 mV (n=17). According to Nerstian formula, the slope of electrochemical gradient in the control was 31 mV/decade (n = 14), but in the hydropic ear it increased to 72.5 mV/decade change in Ca2+ (n = 17). The statistical analysis showed significant difference between the control and hydropic ears. The changes were progressive and became more pronounced as the duration of hydrops prolonged. The cause of hearing loss in the Ménière's disease and the relation between the EP and CA2+ concentration had been discussed.