The influx of pyrophosphate ions into calvaria in vitro

The flux of 32P-labeled inorganic pyrophosphate (PPi) into bone was studied in vitro using Ussing chamber techniques and calvaria from newborn rat pups. Because insignificant hydrolysis and backflux of PPi took place under experimental conditions, it was possible to study the penetration of bone membranes by PP1 unambiguously. At physiological concentrations, the influx was found to be linearly concentration dependent and to follow first order kinetics, apparently a simple diffusion process. In magnitude, the intrinsic constant for influx was found to be approximately one-half that of inorganic phosphate ions under comparable conditions.