Experimental induction and mathematical modeling of Ca²⁺ dynamics in rat round spermatids

Cytosolic Ca concentration ([Ca ]) has an important role in spermatozoa and hence it regulates fertilization. In male germinal cells, there are indirect evidences that this ion could regulate physiological processes in spermatogenesis. Since little is known about Ca²⁺ homeostasis in spermatogenic cells, in this work we propose a mathematical model that accounts for experimental [Ca ] dynamics triggered by blockade of the SERCA transport ATPase with thapsigargin in round rat spermatids, without external Ca and with different extracellular lactate concentrations. The model included three homogeneous calcium compartments and Caase activities sensitive and insensitive to thapsigargin, and it adjusted satisfactorily the experimental calcium dynamic data. Moreover, an extended version of the model satisfactorily adjusted the stationary states of calcium modulated by extracellular lactate, which is consistent with the participation of a low affinity lactate transporter and further lactate metabolism in these cells. Further studies and modeling would be necessary to shed some light into the relation between Ca²⁺-lactate-ATP homeostasis and cell-cell interactions in the seminiferous tubules that are expected to modulate Ca²⁺ dynamics by hormonal factors or energetic substrates in meiotic and postmeiotic spermatogenic cells.