Possible involvement of inositol phosphates and calmodulin in calcitonin-induced stimulation of phosphate transport in LLC-PK1 cells.

The present study investigated the possible involvement of phosphatidylinositol breakdown and Ca2+-calmodulin complex in the calcitonin-induced stimulation of phosphate transport in LLC-PK1 cells. This cell line with calcitonin receptors possesses Na+-dependent phosphate transport and has been employed as a model for studying the mechanism of renal tubular phosphate transport. (Asu1,7) eel calcitonin stimulated the phosphate transport in LLC-PK1 cells in a dose-dependent fashion with accompanying increase of inositol triphosphate (IP3) production. When the cells were preincubated with the potent calmodulin antagonist, w-7 or w-13, the stimulatory effect of calcitonin on phosphate transport was significantly inhibited. These findings indicate that Ca2+-calmodulin complex formed by increased cytosolic Ca2+, which is mobilized from intracellular pools by IP3, may be involved in the signal transduction of calcitonin in these cells.