Vasopressin does not hydrolyze polyphosphoinositides in rabbit papillary collecting tubule cells

Changes in phosphatidylinositol metabolism are suggested to be involved in the mechanism of action of many membrane active hormones. We studied the effect of vasopressin on polyphosphoinositide metabolism in rabbit papillary collecting tubule cells to assess if the hydrolysis of these phospholipids is involved in transmembrane signaling. Rabbit papillary collecting tubule cells grown in monolayers for 5 days were labeled to constant specific activity with [³H]inositol. The temporal changes in [³H]inositol-labeled phospholipids were assessed in response to vasopressin. Similarly, water-soluble inositides were monitored after separation by ion exchange chromatography. Intracellular Ca²⁺ was monitored by use of the fluorescent indicator dye, quin2. Vasopressin (10^-7 M) did not increase the hydrolysis of phosphoinositides over a 5 min period when compared with controls. Similarly, there was no increase in water-soluble phosphoinositols during the same interval. Pretreating the cells with LiCl (10 mM) did not produce any increase in inositol 1-phosphate when stimulated with vasopressin but did in response to bradykinin. Finally, vasopressin did not increase cytosolic Ca²⁺ and did not increase the release of prostaglandin E₂ into the media under our experimental conditions. We conclude that vasopressin does not stimulate prostaglandin E₂ in rabbit papillary collecting tubule cells, does not initiate hydrolysis of polyphosphoinositides and does not increase cytosolic Ca²⁺. Thus these cells lack V₁ receptor coupling mechanisms.