Osmolarity-sensitive release of free amino acids from cultured kidney cells (MDCK)

Summary

The amino acid pool of MDCK cells was essentially constituted by alanine, glycine, glutamic acid, serine, taurine, lysine, β-alanine and glutamine. Upon reductions in osmolarity, free amino acids were rapidly mobilized. In 50% hyposmotic solutions, the intracellular content of free amino acids decreased from 69 to 25mm. Glutamic acid, taurine and β-alanine were the most sensitive to hyposmolarity, followed by glycine, alanine and serine, whereas isoleucine, phenylalanine and valine were only weakly reactive. The properties of this osmolarity-sensitive release of amino acids were examined using³H-taurine. Decreasing osmolarity to 85, 75 or 50% increased taurine efflux from 0.6% per min to 1.6, 3.5 and 5.06 per min, respectively. The time course of³H-taurine release closely follows that of the regulatory volume decrease in MDCK cells. Taurine release was unaffected by removal of Na⁺, Cl⁻ or Ca²⁺, or by treating cells with colchicine or cytochalasin. It was temperature dependent and decreased at low pH. Taurine release was unaffected by bumetanide (an inhibitor of the Na⁺/K⁺/2Cl⁻ carrier); it was inhibited 16 and 67 by TEA and quinidine (inhibitors of K⁺ conductances), unaffected by gadolinium or diphenylamine-2-carboxylate (inhibitors of Cl⁻ channels) and inhibited 50% by DIDS. The inhibitory effects of DIDS and quinidine were additive. Quinidine but not DIDS inhibited taurine uptake by MDCK cells.