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 mechanisms both for uptake and osmotically regulated release, we investigated their localization in polarized cells. Methods. An immortalized epithelial cell line derived from the thick ascending limb of Henle's loop (TALH) was used to examine the transport characteristics of the apical and basolateral plasma membranes for osmotic regulation 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 > glycerophosphoryl choline (GPC). When extracellular osmolarity was decreased, then sorbitol was released on the apical side, whereas betaine and myo-inositol efflux occurred on the basolateral side. GPC release showed no preference of either side. Taurine did not seem to be necessary for osmoregulation under these conditions. Osmotically regulated myo-inositol and betaine uptake was located on the apical side, and choline uptake took place on both sides equally. Conclusion. These results show that in renal epithelial cells, both osmotically induced release and the uptake of organic osmolytes are divided between the apical and the basolateral sides. This might be important for volume regulation.