IN-VITRO ELECTROGENIC K SECRETION IN THE FROG SEMICIRCULAR CANAL - ABSENCE OF EFFECT OF STREPTOMYCIN

In vitro, the frog semicircular canal secretes an endolymph-like fluid , i.e. a K-rich, positively polarized fluid. This electrogenic K secre tion involved basolateral Na+,K+-ATPase and Na-K-Cl co-transporter and a luminal protein possessing sulfhydryl groups blocked by N-ethylmale imide. Steptomycin, an ototoxic antibiotic, is known to block the non- specific, mechano-dependent channels in the sensory cells of the ampul la of the semicircular canal. The aim of the present study was to inve stigate the possible effect of streptomycin on the K fluxes in the amp ulla of the semicircular canal. The posterior frog semicircular canal was isolated and the lumen was filled with perilymph-like solution con taining: or not containing 0.5 mM streptomycin. The luminal K concentr ation and the transepithelial potential were measured and the unidirec tional K fluxes calculated. The K influxes (into the lumen, pmoles/min /mm(2)) were 114 +/- 25.9 and 111 +/- 3.2 (mean +/- SE, n = 3) in the absence and presence of streptomycin, respectively. The transepithelia l 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 t ogether with luminal streptomycin, no further alteration occurred as c ompared with the effect of ouabain alone. These results suggest that, in these conditions, the sensory organ does not have a major role in t he endolymphatic K secretion in the ampulla of the frog semicircular c anal.