Bumetanide-induced enlargement of the intercellular space in the stria vascularis requires an active Na⁺-K⁺-ATPase

Objective - Loop diuretics such as bumetanide and furosemide cause an acute enlargement of the intrastrial space of the stria vascularis, with an associated decline in the endocochlear DC potential (EP). The aim of this study was to determine the role played by the Na⁺-K⁺-ATPase in the bumetanide-induced enlargement of the intrastrial space, and to examine the importance of the balance between the activities of the Na⁺-K⁺-2Cl^- cotransporter and the Na⁺-K⁺-ATPase to the physiological function of the stria vascularis. Material and methods - Albino guinea pigs were used in experiments involving perilymphatic perfusion, EP measurement and electron microscopy. The effects of bumetanide on the stria vascularis were examined following inhibition of the Na⁺-K⁺-ATPase by ouabain. Ouabain was administered to the perfusate and, when the EP reached 0 mV, both ouabain and bumetanide were administered. Results - Although there was no enlargement of the intrastrial space, vacuoles were apparent in marginal cells. The vacuolar change in marginal cells was similar to that caused by ouabain alone. Conclusion - This study indicates that the enlargement of the intrastrial space requires not only the blockade of the Na⁺-K⁺-2Cl^- cotransporter but also normal activity of the Na⁺-K⁺-ATPase, and suggests that the bumetanide-induced enlargement of the intrastrial space resulted from the imbalance between the activities of the Na⁺-K⁺-2Cl^- cotransporter and the Na⁺-K⁺-ATPase.