Hydrogen peroxide inhibits gap junctional coupling and modulates intracellular free calcium in cochlear Hensen cells

The double whole-cell patch-clamp configuration was applied to analyze gap junctional conductance (Gj) of isolated pairs of cochlear supporting Hensen cells of guinea pig under control conditions and in the presence of hydrogen peroxide (H2O2). Under control conditions, the dependence of Gj on transjunctional voltage (Vj) appeared to vary between different cell pairs with a maximum value of about 40 nS at Vj close to 0 mV. The voltage dependence and the maximum amplitude of Gj stayed constant for at least 2 hr. Addition of H2O2 to the bath at concentrations above 0.08 mm caused a significant decrease of Gj, but the membrane potential of about -30 mV was not affected. In parallel, intracellular free calcium ([Ca2+]i) was followed using fura-2. At 0.8 mm H2O2, a sustained increase of [Ca2+]i was observed, while 0.08 mm H2O2 evoked an oscillating-like behavior of [Ca2+]i. We propose that the H2O2-evoked inhibition of gap junctional coupling of Hensen cells is closely related to pathophysiological conditions such as noise- induced hearing loss, aminoglycoside-related ototoxicity and presbycusis, which are known to be associated with production of free radicals.