[Study on voltage-sensitive current of spiral ganglion cells in mice organ of Corti culture].

OBJECTIVE

To investigate the property of voltage-sensitive current in cochlear spiral ganglion cells of the C57BL/10J mice, an inbred strain which develops early onset hearing loss.

METHODS

Organotypic cultures of organ of Corti were prepared from neonatal mice 0-5 days of age. Whole-cell current and voltage clamp techniques were used to study Na+, K+ and Ca2+ currents of the spiral ganglion cells in culture.

RESULTS

Cultures were maintained for 8-48 hours before use. Ganglion cells were identified first through their anatomical positions and finally through fast negative Na+ current. Spontaneous action potentials were recorded from some ganglion cells (4 out of 39). When present, spontaneous rates were around 20 spikes/sec, and might be as high as 135 spikes/sec. The mean resting potential was (-55 +/- 5) mV (n = 39). Under voltage clamp conditions, transient inward currents (negative) and outward (positive), steady-state voltage-dependent currents were recorded in normal HBSS. Rapid inward currents were totally blocked by 300 nM TTX applied locally to the culture. Inward currents recovered quickly after TTX wash out suggesting that the transient inward current was carried by Na+. The mean maximum amplitude of Na+ current was (-2.0 +/- 1.1) nA (n = 39) recorded in HBSS. Adding TEA (10 mmol/L) and 4-AP (0.15 mmol/L) to the bath solution or replacing K+ with Ca+ in the pipette solution partly blocked the sustained outward current. This suggests that the outward current was carried by K+. The mean maximum amplitude of K+ was (3.0 +/- 1.3) nA (n = 39) with 140 mM K+ in the pipette. Inward Ca2+ current was recorded in Ba2+ solution which mean peak amplitude was (-1.0 +/- 0.7) nA (n = 20). Ca2+ currents were reversibly blocked by 100 microM Cd2+.

CONCLUSION

Whole cell recordings from spiral ganglion neurons can be obtained from organotypic cultures of the organ of Corti. Fast Na+ current, sustained K+ current and L-type Ca2+ current were recorded in the spiral ganglion cells cultured for 1-2 days. Whole cell recording showed that cochlea spiral ganglion cells can generate spontaneous action potential one day after birth and the firing rates could reach levels equal to those recorded in vivo.