NUCLEOSIDE UPTAKE IN MALE GERM-CELLS OF THE POLYCHAETE NEREIS-VIRENS

Uptake of inosine and guanosine was measured in male germ cells of the polychaete Nereis virens at different stages of development. In sperm atogonia I (spg I) and spermatid stages, total inosine uptake at 12 de grees C and ambient concentrations of 100 mu mol/l was relatively low (10-50 nmol . ml of packed cell volume pcv(-1). h(-1)). A rapid increa se (150-300 nmol . ml of pcv(-1). h(-1)) was found during transition f rom spg I to spg II with a subsequent decline to low values (10-30 nmo l . ml of pcv(-1). h(-1)) in spermatocyte and spermatid stages. This t ransient increase may be related to the proliferative activity of spg I stages leading to spg II stages, which increases the demand of purin e precursors for nucleic acid synthesis. Inosine uptake of spermatozoa stages was extremely variable, and high uptake rates (10-300 nmol . m l of pcv(-1). h(-1)) were found in some, but not in all, cases. In all stages the uptake rates for guanosine remained at a lower level (belo w 75 nmol . ml of pcv(-1). h(-1)), and no clear stage specific pattern was evident except for low values (<10 nmol . ml of pcv(-1). h(-1)) i n motile spermatozoa. For both nucleosides, two uptake components were identified: a linear component (measured at medium concentrations up to 300 mu mol/l) and a saturable component (app. k(m): 9-60 mu mol/l). The latter was inhibited by iodo-acetamide suggesting the presence of an ATP-dependent facilitated transport mechanism. The presence of the two uptake components was related to the stage of gamete development: the saturable uptake component present in early spg I changed to a li near uptake in late spg I. In spg II stages, both uptake components we re present while in spermatocytes, only the saturable component was pr esent. Spermatids and early spermatozoa showed only a linear uptake. I n the coelomic fluid, guanosine (0.5-20 mu mol/l) and inosine (>3 mu m ol/l) were the main nucleosides; during spg II and spermatocyte stages , inosine reached high concentrations (100-1000 mu mol/l).