Polarized function of thick ascending limbs of Henle cells in osmoregulation

Background. Organic osmolytes are necessary for osmoregulation in mammalian kidney. Since renal epithelial cells in many cases possess specific mechan isms both for uptake and osmotically regulated release, we investigated the ir localization in polarized cells. Methods. An immortalized epithelial cell line derived from the thick ascend ing limb of Henle's loop (TALH) was used to examine the transport character istics of the apical and basolateral plasma membranes for osmotic regulatio n of organic osmolytes. Cells were cultured on filters in a two-compartment chamber: Results. In culture under hypertonic conditions the TALH cells accumulated in the following balance: sorbitol > betaine = myo-inositol > glycerophosph oryl choline (GPC). When extracellular osmolarity was decreased, then sorbi tol was released on the apical side, whereas betaine and myo-inositol efflu x occurred on the basolateral side. GPC release showed no preference of eit her side. Taurine did not seem to be necessary for osmoregulation under the se conditions. Osmotically regulated myo-inositol and betaine uptake was lo cated on the apical side, and choline uptake took place on both sides equal ly. Conclusion. These results show that in renal epithelial cells, both osmotic ally induced release and the uptake of organic osmolytes are divided betwee n the apical and the basolateral sides. This might be important for volume regulation.