Research on sodium transport in the endolymphatic sac

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(Study on non-selective cation channel in the ES) The properties of a non-selective cation channel in the endolymphatic sac (ES) were investigated using patch clamp technique. The channel currents were measured in freshly isolated epithelial cells from the intermediate portion of the endolymphatic sac (ES) in the guinea pig by the single-channel recording technique. The non-selective cation channel had a conductance of 24.0? 1.3pS (n=8). The relative ionic permeability of the channel was in the order K^+=Na^>Ca^<2+>>Cl^-. ATP (1 mM) activated the channel at intracellular Ca^<2+> concentrations from 0.6 iM to 10iM. The results suggest that the non-selective cation channel in the ES may contribute to the regulation of ionic balance and volume of the ES by absorbing Na^+ under certain pathological situations increasing the intracellular Ca^<2+> concentration.(Microfluorometrical study on Na+ transport in the ES) The properties of Na+ transport in the ES epithelial cells were investigated using SFBI/AM fluorescence measurement. The intracellular Na concentration was increased by the suppresion of Na^+-K^+ ATPase such as the application with K^+-free solution and ouabain. ES epithelial cells in the intermediate portion were classified into two types, based on the activity of Na^+-K^+ ATPase. Two type cells were almost equally distributed in number. The epithelial cells with a higher activity corresponded to strongly mitochondria-stained cells (type 1cells). The results indicates that type 1cells play important roles in sodium transport of the ES. The simulation of Na transport capacity in the ES epithelial cells on the basis of the present experimental results supports the morphological data in the experimentally induced endolympatic hydrops.