Calcium and Phosphorus Accumulation in Spirostomum ambiguum

SYNOPSIS. Spirostomum ambiguum is known to contain Ca phosphate as apatite. Tracer experiments with 32P and 45Ca showed that much of the Ca that enters the animal is inexchangeable. About 20% exchanges in the 1st few days but after 42 days only 50% of the original isotope content has been lost. This process seemed independent of temperature, Ca and K concentration, and of whether the animals were starved or fed. It is postulated that the firmly bound Ca is in the form of apatite. By use of both isotopes simultaneously it was shown that some of the Ca uptake was linked with phosphate uptake. However, there appear to be at least one, probably 2 compartments of Ca uptake independent of phosphate uptake. The experiments suggest there being in all 3 compartments of Ca uptake: one firmly bound as apatite; one slightly less firmly bound in some other form (perhaps carbonate); and a last freely exchangeable fraction. The P was found in 2 compartments: one bound to Ca; the other freely exchangeable. Autoradiography and histochemical tests localized the Ca phosphate deposits in the “endoplasm”, the ectoplasm and nuclear material being free of such deposits. Identification of these deposits in electron micrographs is discussed. It is suggested that these deposits may be waste products possibly derived from mitochondri***al accumulations.