Intracellular pH in sperm physiology

Abstract

Intracellular pH (pHi) regulation is essential for cell function. Notably, several unique sperm ion transporters and enzymes whose elimination causes infertility are either pHi dependent or somehow related to pHi regulation. Amongst them are: CatSper, a Ca2+ channel; Slo3, a K+ channel; the sperm-specific Na+/H+ exchanger and the soluble adenylyl cyclase. It is thus clear that pHi regulation is of the utmost importance for sperm physiology. This review briefly summarizes the key components involved in pHi regulation, their characteristics and participation in fundamental sperm functions such as motility, maturation and the acrosome reaction.

Single cell imaging reveals that the motility regulator speract induces a flagellar alkalinization that precedes and is independent of Ca2+ influx in sea urchin spermatozoa

“…Therefore, we investigated if an alkalinization could mimic these responses. We found that a 10 mM NH 4 Cl addition evoked a [Ca 2+ ]i increase in sperm head and flagellum (Fig. 6A).…”

“…To allow comparison and averaging independent spermatozoa, BCECF and Fluo-4 data were equally treated and normalized using the maximal value obtained with NH 4 Cl or ionomycin, respectively, per ROI. In BCECF/Fluo-4 parallel measurements, fluorophores were distinguished according to the cell response to NH 4 Cl or ionomycin, which were added consecutively at the end of each experiment. As chemotaxis occurs during the first 3 s of the speract response [3], only the first 3 s of the pHi response were used for the kinetic analysis.…”

“…Fig. 1A shows a typical field with BCECF-loaded sperm before and after 100 nM speract stimulation, and following NH 4 Cl addition as an alkalinization control. At the right of the images we show the raw traces of the speract-induced pHi changes from the indicated sperm.…”

“…Speract induces [Ca 2+ ]i oscillations that modulate flagellar beating and sperm swimming [2,3]. However, how pHi influences sea urchin sperm motility is not fully understood [4][5][6]. It has been proposed that the pHi increase might be caused by the activation of the voltage dependent Na + /H + exchanger (NHE) localized in the sperm flagella [7], upon the speract-induced hyperpolarization [8].…”

Flagellar ion channels of sperm: similarities and differences between species

“…Noncapacitated epididymal murine spermatozoa are slightly depolarized at about −40 mV, however they hyperpolarize up to −60 mV upon capacitation [137]. This effect is attributed to potassium permeability and two members of the Slo family of potassium channels have been recently proposed to play a role in this process [21,25,26,29,31,33,[138][139][140][141]. Slo3 (Kcnu1), a pH-sensitive, calcium-independent and weakly voltage-sensitive channel, has been identified as the principal potassium channel in murine sperm [25,26,29,31,33,[141][142][143].…”