Calcium signalling during RVD of kidney cells

The balance of a high extracellular osmolarity in the kidney medulla is mai nly based on an accumulation of organic osmolytes in the cells. The regulat ion of cell volume during hypotonic conditions results in a release of orga nic osmolytes - a process that is partly calcium-dependent, Using calcium-s ensitive fluorescent dye and confocal laser scanning microscopy, we have in vestigated calcium signalling during regulatory volume decrease (RVD) in ki dney cells. In rat inner medullary collecting duct (IMCD) cells in primary culture, hypotonic stress induced a calcium release from intracellular stor es that preceded calcium entry from the extracellular milieu. Hyposmotic st ress had no effect on the cellular IP3 content. Preincubation with 100 mu m ol/l ETYA (a non-metabolizible derivative of arachidonic acid), however, re duced the calcium response to hypotonic stress as well as the RVD. Blocker of voltage-dependent calcium channels (verapamil, diltiazem, and nifedipine ) in the concentration of 40 mu mol/l reduced partly the calcium response. SKF-96365, an inhibitor of receptor-mediated calcium channels, also attenua ted the calcium influx. In conclusion, swelling of IMCD cells increases int racellular calcium by release from intracellular stores and entry across th e cell membranes. The signalling involves arachidonic acid metabolism. Copy right (C) 2000 S. Karger AG, Basel.