Effects of Vitamin C and Hydrogen Dioxide on the Electric Current of Large-conductance Calcium-activated Potassium Channels in Isolated Outer Hair Cells of Old Guinea Pigs’ Cochlears / 听力学及言语疾病杂志

ABSTRACT

Objective To study the effects of hydrogen dioxide (oxygen free radical donator) and vitamin C (oxygen free radical scavenger) on the electric current of large conductance calcium -activated potassium channels (BKCa channels) in isolated outer hair cells in aging guinea pigs .Methods Acute enzyme was used to isolat outer hair cells of aging guinea pigs ,in which of BKCa channel's electric current was observed and recorded by whole-cell recording mode of patch -clamp .After recording the stable and normal electric current of BKCa channels ,added H2 O2 dilution (0 .2 mmol/L) 40 μl in the 2 ml chambers within freshly isolated outer hair cells so that the concen‐tration of H2 O2 in the balneum would be 4 μmol /L .The groups(n=5) received individually vitamin C solution (5 mg/ml) 0 ,10 ,20 ,40μl in the 2 ml chambers within freshly isolated outer hair cells so that the concentration of vi‐tamin C in the balneum would be 0 ,25 ,50 ,100 μg /ml ,observing and recording the effects of different concentration of vitamin C to electric current of BKCa channels .Results ①In the w hole-cell mode of patch -clamp ,the rapid activation and non-deactivation electric current with a string of large amplitude was recorded ,above -40~ -30 mV activation voltage .The electric current increased with the increasing membrane potential .The amplitude in‐creased continuously and performed characteristics of outward rectification .When the concentration of IbTX was 100 nmol /L ,the activity of the channel was completely blocked and confirmed BKCa channel's electric current .②Medication within three minutes ,when VT was +50 mV ,the BKCa channels'the maximum peak current densities of 4 μmol /L H2 O2 group rose from 22 .09 ± 0 .27 PA /PF to 43 .53 ± 1 .09 PA/PF ,amplification was 97 .06% .In H2 O2 4 μmol /L + vitamin C with different concentrations as 25 ,50 ,100 μg/ml groups ,the BKCa channels'elec‐tric current performed about concentration-dependent inhibition ,and electric current's amplitude and peak current density decreased with the increasing concentration of vitamin C ,the I-V curves were reduced .However ,this still could not be recovered to the normal levels .Conclusion The oxygen free radical /BKCa exists in the process .The vitamin C as oxygen free radical scavenger can reverse the process to a large extent .