| Abstract | CatSpers are Calcium (Ca) channels that are located along the principal piece of mammalian sperm flagella and are directly linked to sperm motility and hyperactivation. It has been observed that Ca induced entry through CatSper channels triggers a tail to head Ca propagation in mouse sperm, as well as a sustained increase of Ca in the head region. Here, we develop a mathematical model to investigate this propagation and sustained increase in the head region. A 1-d reaction-diffusion model tracking intracellular Ca with flux terms for the CatSper channels, a leak flux, and plasma membrane Ca clearance mechanism is studied. Results of this simple model exhibit tail to head Ca propagation, but no sustained increase in the head region. Therefore, in this model, diffusion alone cannot account for these experimentally observed results. It has been proposed that the Ca influx from the CatSper channels may induce Ca release in the head region. We test this hypothesis by examining the possible role of Ca induced Ca release from the Redundant Nuclear Envelope (RNE), an inositol-1,4,5-triphosphate (IP3) gated Ca store in the neck. The simple model is extended to include an equation for IP3 synthesis, degradation, and diffusion, as well as flux terms for Ca in the RNE. When IP3 and the RNE are accounted for, the results of the model exhibit a tail to head Ca propagation as well as a sustained increase of Ca in the head region. |
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