[Differences in furosemide-induced changes of summating potential and endocochlear potential in guinea pigs]

To investigate the physiological properties of summating potential (SP) and to compare the different changes between SP and endocochlear potential (EP) induced by Furosemide in guinea pigs.

SP in response to clicks with alternative polarities at 105 dB peSPL was recorded from a electrode in the facial nerve canal. EP was measured with a glass microelectrode in the basal turn of the cochlea. SP and EP were observed simultaneously and continuously after injection of Furosemide or the solution of Furosemide-bovine serum albumin injected into the jugular vein of the animal.

Before furosemide application, only SP could be recorded with small or without +SP. After furosemide injection, EP declined dramatically followed by reduction of the -SP which quickly vanished, while +SP appeared or the amplitude increased. When EP recovered to a certain level, +SP disappeared or dramatically decreased and then -SP reappeared. The amplitude of -SP increased progressively with EP recovery. Both -SP and EP recovered to the pre-injected level in 60 min after the furosemide application.

The results suggest that Furosemide induced distinct changes of -SP and +SP, the two components of SP. The changes of -SP amplitude was consistent with that of the EP value, while the changes of +SP amplitude were contrary to that of the EP value.