Abstract
Polyamines are ubiquitous polycationic compounds that are highly charged at physiological pH. While passing through the epididymis, sperm lose their capacity to synthesize the polyamines and, upon ejaculation, again come into contact with the polyamines contained in the seminal fluid, unleashing physiological events that improve sperm motility and capacitation. In the present work, we hypothesize about the influence of polyamines, namely, spermine, spermidine, and putrescine, on the activity of sperm channels, evaluating the intracellular concentrations of chloride [Cl−]i, calcium [Ca2+]i, sodium [Na+]i, potassium [K+]i, the membrane Vm, and pHi. The aim of this is to identify the possible regulatory mechanisms mediated by the polyamines on sperm-specific channels under capacitation and non-capacitation conditions. The results showed that the presence of polyamines did not directly influence the activity of calcium and chloride channels. However, the results suggested an interaction of polyamines with sodium and potassium channels, which may contribute to the membrane Vm during capacitation. In addition, alkalization of the pHi revealed the possible activation of sperm-specific Na+/H+ exchangers (NHEs) by the increased levels of cyclic AMP (cAMP), which were produced by soluble adenylate cyclase (sAC) and interact with the polyamines, evidence that is supported by in silico analysis.
Highlights
Sperm from mammals are produced and differentiate in the testis
Sperm are morphologically mature at this point, but they lack of fertilization capacity, which is acquired in the epididymis [5,6]
Once the sperm pass through the epididymis, they are stored in the vas deferens waiting to be ejaculated, without any contact with extracellular polyamines [1,6]
Summary
Sperm from mammals are produced and differentiate in the testis. At this stage, the sperm cell possesses all of the enzymatic machinery needed to synthesize the polyamines [1].Polyamines are ubiquitous polycationic compounds; human seminal spermine has a concentration of 3 mM, while spermidine and putrescine have approximately ten times less [2].These small molecules are highly charged at physiological pH [3] and supposedly enter the cytoplasm through cell-surface heparin sulfate proteoglycans and endocytosis [4].Once the sperm cells have differentiated, they leave the testis, emerge, and pass through the epididymis. Sperm from mammals are produced and differentiate in the testis At this stage, the sperm cell possesses all of the enzymatic machinery needed to synthesize the polyamines [1]. Polyamines are ubiquitous polycationic compounds; human seminal spermine has a concentration of 3 mM, while spermidine and putrescine have approximately ten times less [2]. These small molecules are highly charged at physiological pH [3] and supposedly enter the cytoplasm through cell-surface heparin sulfate proteoglycans and endocytosis [4]. Once the sperm pass through the epididymis, they are stored in the vas deferens waiting to be ejaculated, without any contact with extracellular polyamines [1,6]
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