Kinetic analysis of calcium desaturation curves from isolated kidney cells.

This paper provides mathematical solutions for calculating calcium fluxes and compartments in isolated kidney cells from calcium-45 desaturation curves. In contrast to other available methods, these solutions allow the calculation of kinetic parameters even if isotopic equilibrium has not been reached at the beginning of the desaturation period. To test the validity of the method, calcium-45 desaturation experiments were performed in isolated kidney cells after labeling periods of 30, 60, 90, or 120 min. Even though the calcium-45 desaturation curves differ with different labeling times, the respective values of the calculated parameters are practically identical. The optical labeling period was found to lie between 60 and 120 min. Since this new method does not require initial isotopic steady state, it allows a formal kinetic analysis of tracer desaturation curves even after short periods of labeling.