Abstract

Intracellular calcium ion (Ca²⁺) homeostasis is a fundamental regulatory mechanism governing the functional competence of spermatozoa, playing a critical role in the cascade of events necessary for successful fertilization. This study investigates the complex regulatory mechanisms that maintain and modulate the precise spatio-temporal Ca²⁺ signals within the sperm cell, which lacks the transcriptional and translational machinery of somatic cells. We employed a combination of fluorescence imaging, patch-clamp electrophysiology, and pharmacological manipulation to characterize the activity of key Ca²⁺ channels and transporters, including the CatSper channel, plasma membrane Ca²⁺-ATPases (PMCAs), and Na⁺/Ca²⁺ exchangers (NCX). Our findings highlight that the coordinated activity of these components establishes distinct Ca²⁺ microdomains essential for sequential physiological processes. Specifically, a controlled increase in intracellular Ca²⁺ is shown to be indispensable for sperm capacitation, the induction of hyperactivated motility, and the acrosome reaction. Dysregulation of this tight Ca²⁺ control is directly correlated with impaired motility and reduced fertilizing capacity, underscoring the profound biological significance of Ca²⁺ homeostasis. These results provide a comprehensive model of the Ca²⁺ signaling toolkit in spermatozoa and offer potential targets for diagnosing and treating male infertility.