Quantitative studies on the effect of prostacyclin on freshly isolated rat osteoclasts in culture

Prostaglandins exert marked but transient inhibitory effects on bone resorption. The present study examines the effects of prostacyclin (0.15 to 25 μM) on the morphology of freshly disaggregated rat osteoclasts. An area descriptor, ρ, represented changes in total cell spread area, and a motility descriptor, μ, represented overall changes in cell motility. The application of prostacyclin intercepted the trend of an increasing cell spread area with time and produced a transient reduction of ρ, an R effect. Its magnitude depended upon concentration and was marked at 25 μM prostacyclin. The subsequent recovery (+0.8/min) of ρ at this concentration resembled the persistent spreading seen in the absence of the agonist. There was also a sustained decrease in μ to approximately 60% of its pretreatment value (a Q effect) following the application of 25 μM prostacyclin. The extracellular application of 20 mM [Ca²⁺] produced a similarly transient cell retraction preceded by a rise of cytosolic [Ca²⁺], but without a corresponding decrease in μ. In contrast, prostacyclin did not elevate cytosolic [Ca²⁺], suggesting the triggering of an alternative transduction pathway. A fully reversible retraction together with incomplete quiescence may explain the transience characteristic of the antiresorptive action of prostacyclin.