In vitro Electrogenic K Secretion in the Frog Semicircular Canal: Absence of Effect of Streptomycin

Abstract

In vitro, the frog semicircular canal secretes an endolymph-like fluid, i.e. a K-rich, positively polarized fluid. This electrogenic K secretion involved basolateral Na⁺, K⁺ -ATPase and Na-K-Cl co-transporter and a luminal protein possessing sulfhydryl groups blocked by N-ethylmaleimide. Steptomycin, an ototoxic antibiotic, is known to block the non-specific. mechano-dependent channels in the sensory cells of the ampulla of the semicircular canal. The aim of the present study was to investigate the possible effect of streptomycin on the K fluxes in the ampulla of the semicircular canal. The posterior frog semicircular canal was isolated and the lumen was filled with perilymph-like solution containing or not containing 0.5 mM streptomycin. The luminal K concentration and the transepithelial potential were measured and the unidirectional K fluxes calculated. The K influxes (into the lumen, pmoles/min/mm²) were 114 ± 25.9 and 111 ±3.2 (mean ± SE, n = 3) in the absence and presence of streptomycin, respectively. The transepithelial potential was not altered (4.0 ± 1.08 mV versus 3.4 ± 1.03 mV, n = 3). When ouabain (10⁻- ³ M) was added to the basolateral solution together with luminal streptomycin, no further alteration occurred as compared with the effect of ouabain alone. These results suggest that, in these conditions, the sensory organ does not have a major role in the endolymphatic K secretion in the ampulla of the frog semicircular canal.

Key Words:

• inner ear fluids
• endolymphatic potential
• K transport
• ototoxicity