Arachidonic acid as a second messenger for hypotonicity-induced calcium transients in rat IMCD cells

In rat inner medullary collecting duct (IMCD) cells in primary culture, hypotonic stress induces Ca2+ transients consisting of an early peak phase caused by a Ca2+ release from intracellular stores and a subsequent plateau phase that involves Ca2+ entry from the extracellular milieu. In the present study, the mechanisms by which cell swelling is transduced into the Ca2+ release were investigated. The free intracellular Ca2+ concentration ([Ca2+]i) was measured using the fluorescent dye fura-2 and cell volume using a confocal laser scanning microscope. In control experiments, after reduction of extracellular osmolarity from 600 to 300 mosmol/l, by omission of sucrose, [Ca2+]i rapidly increased from 106 +/- 9 nmol/l to a peak value of 405 +/- 22 nmol/l (P