Abstract
The role of Na+ fluxes through voltage-gated sodium channels in the regulation of sperm cell function remains poorly understood. Previously, we reported that several genes encoding voltage-gated Na+ channels were expressed in human testis and mature spermatozoa. In this study, we analyzed the presence and function of the TTX-resistant VGSC α subunit Nav1.8 in human capacitated sperm cells. Using an RT-PCR assay, we found that the mRNA of the gene SCN10A, that encode Na v1.8, was abundantly and specifically expressed in human testis and ejaculated spermatozoa. The Na v1.8 protein was detected in capacitated sperm cells using three different specific antibodies against this channel. Positive immunoreactivity was mainly located in the neck and the principal piece of the flagellum. The presence of Na v1.8 in sperm cells was confirmed by Western blot. Functional studies demonstrated that the increases in progressive motility produced by veratridine, a voltage-gated sodium channel activator, were reduced in sperm cells preincubated with TTX (10 μM), the Na v1.8 antagonist A-803467, or a specific Na v1.8 antibody. Veratridine elicited similar percentage increases in progressive motility in sperm cells maintained in Ca2+-containing or Ca2+-free solution and did not induce hyperactivation or the acrosome reaction. Veratridine caused a rise in sperm intracellular Na+, [Na+]i, and the sustained phase of the response was inhibited in the presence of A-803467. These results verify that the Na+ channel Na v1.8 is present in human sperm cells and demonstrate that this channel participates in the regulation of sperm function.
Highlights
Ion channels play a central role in the regulation of sperm intra- and inter-cellular signaling [1,2,3,4,5,6,7,8,9]
We previously found, using end-point RT-PCR, that SCN10A was expressed in human testis and sperm cells [18,21]
After PCR amplification for 30 cycles with any of the specific primer pairs, the SCN10A mRNA was only detected in human testis
Summary
Ion channels play a central role in the regulation of sperm intra- and inter-cellular signaling [1,2,3,4,5,6,7,8,9]. Na+ channels should play an important role in sperm, as the gradient of this ion across the plasma membrane plays a central role in the regulation of membrane potential (Em), a parameter that govern the rate and direction of ion-flow through channels and exchangers and modulates the intracellular pH (pHi) [16,17]. In this context, the presence of epithelial Na+ channels of the ENaC family [17] and of voltage-gated Na+ channels (VGSC) [18] has been demonstrated in sperm cells, their role remain poorly understood
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