[The effects of streptomycin on the calcium influx in SGCs during depolarization]

To examine the effect of streptomycin on the calcium influx in spiral ganglion cells (SGCs) during depolarization and the differences among different concentrations of streptomycin and SGCs sources with the aim of exploring the mechanism of acute streptomycin ototoxicity.

The SGCs of guinea pig cochlea were isolated using an enzyme-machine method and loaded with 10 mumol/L Fluo-3/AM for 30 min at 37 degrees C. Dissociated SGCs loaded with Fluo-3 were examined with a confocal microscope (ACAS Ultima, USA) using a 20 x objective lens and linear scan mean. The fluorescent images collected every 5-sec for a total of 300 sec were stored in a computer. The fluorescent intensity of the images was analyzed by a software cooperated with the confocal microscope, and a curve of fluorescent intensity changes against time was obtained.

The [Ca2+]i of SGCs was steady under the perfusion with standard extracellular solution. The [Ca2+]i of SGCs increased in 12/14 cells under the perfusion with 150 mmol/L high potassium solution, but increased in only 1/10 cells induced by the high potassium calcium free solution. After treating with 1 mmol/L, 0.1 mmol/L, 0.01 mmol/L streptomycin, the [Ca2+]i of the SGCs perfused with the potassium solution was increased in 0/9, 6/14, 7/13 cells, respectively. After the SGCs were treatment with 0.02 mmol/L streptomycin, the [Ca2+]i of the SGCs perfused with the high potassium solution was increased in 5/10 SGCs from the apical turn and in 0/15 SGCs from the basal turn.

Perfusion with high potassium media can result in obviously increased [Ca2+]i of the SGCs, and the increase of the [Ca2+]i in the SGCs may originate from the extracellular calcium influx. The calcium influx can be blocked by streptomycin and such effects depend on streptomycin concentrations and SGCs sources.