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Alberto Darszon, Juan J Acevedo, Blanca E Galindo, Enrique O Hernández-González, Takuya Nishigaki, Claudia L Treviño, Chris Wood, and Carmen Beltrán

Ion channels are extraordinarily efficient machines that move ions in diversely controlled manners, allowing cells to rapidly exchange information with the outside world and with other cells. Communication is the currency of fertilization, as it is of most fundamental cell signaling events. Ion channels are deeply involved in the dialogue between sperm, its surroundings, and the egg. How sperm swim, find the egg and fertilize it depend on ion permeability changes modulated by environmental cues and components of the egg outer layer. Different ion channels distinctly localized in these tiny, amazing cells perform specific decoding functions that shape the sophisticated behavior of sperm. It is not surprising that certain sperm ion channels are turning out to be unique. New strategies to characterize sperm ion transport have opened exciting possibilities to dissect sperm–egg signaling and unveil novel contraception targets.

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Sandra Hernández-Garduño, Julio C Chávez, Arturo Matamoros-Volante, Yoloxochitl Sánchez-Guevara, Paulina Torres, Claudia L Treviño, and Takuya Nishigaki

In brief

Hyperpolarization of the membrane potential is a crucial step for mammalian sperm maturation. This work demonstrates that this membrane potential change likely activates a sperm-specific sodium/proton exchanger to induce alkalization in mouse sperm flagellum.

Abstract

The sperm-specific sodium/proton exchanger (sNHE) is an indispensable protein for male fertility in mammals. Nevertheless, it is still unknown how mammalian sNHE is regulated. Evidence obtained from sea urchin sNHE indicates that hyperpolarization of plasma membrane potential (Vm), which is a hallmark of mammalian capacitation, positively regulates the sNHE. Therefore, we explored the activity of sNHE in mouse and human sperm by fluorescence imaging of intracellular pH (pHi) with a ratiometric dye, SNARF-5F. A valinomycin-induced Vm hyperpolarization elevated sperm flagellar pHi of WT mouse but not in sNHE-KO mouse. Moreover, this pHi increase was inhibited in a high K+ (40 mM) medium. These results support the idea that mouse sNHE is activated by Vm hyperpolarization. Interestingly, we observed different types of kinetics derived from valinomycin-induced alkalization, including some (30%) without any pHi changes. Our quantitative pHi determinations revealed that unresponsive cells had a high resting pHi (>7.5), suggesting that the activity of mouse sNHE is regulated by the resting pHi. On the other hand, valinomycin did not increase the pHi of human sperm in the head or the flagellum, regardless of their resting pHi values. Our findings suggest that the regulatory mechanisms of mammalian sNHEs are probably distinct depending on the species.

Free access

Ayelen Moreno-Irusta, Esteban M Dominguez, Clara I Marín-Briggiler, Arturo Matamoros-Volante, Ornella Lucchesi, Claudia N Tomes, Claudia L Treviño, Mariano G Buffone, Ramiro Lascano, Luis Losinno, and Laura C Giojalas

Sperm chemotaxis may facilitate the finding of the oocyte. Only capacitated spermatozoa can orient their movement by chemotaxis, which as well as capacitation, is regulated in part by the cAMP-PKA pathway. Reactive oxygen species (ROS) are produced during sperm capacitation which is closely related to chemotaxis. Then, the ROS participation in the chemotactic signaling can be expected. Here we studied the role of ROS in the chemotaxis signaling of equine spermatozoa which produce high quantities of ROS because of their energy metabolism. The level of capacitated and chemotactic spermatozoa was increased with 0.1 and 0.2 mM hydrogen peroxide (H2O2), which was involved in the chemotactic signaling. By combining a concentration gradient of H2O2 with inhibitors/chelators of some of the signaling pathway elements, we showed that the activation of NOX (membrane NADPH oxidase) increases the intracellular ROS which activate the chemotaxis AMPc-PKA pathway. Our results provide evidence about the participation of ROS in the chemotactic signaling mediated by progesterone (P).