Molecular identification of Ca(2+)channels in human sperm

Abstract

A bstractThe acrosom e reaction is a Ca 2+ -dependent exocytotic process that is a prerequisite step for fertilization. External calcium entry through voltage-activated Ca 2+ channels is know n to be essential in inducing the acrosome reaction of mammalian sperm atozoa. Due to their com plex geom etry, however, electrophysiological identification of sperm Ca 2+ channels has been lim ited. Here we identified Ca 2+ channel m RNAs expressed in m otile hum an sperm using RT-PCR and their levels w ere compared using RNase protection assays. L-type, non-L-type, and T-type C a 2+ channel m RNAs w ere detected by RT-PCR using degenerate prim ers. Cloning and sequencing of the PCR products revealed α1B, α1C, α1E, α1G , and α1H sequences. RT-PCR using specific prim ers repeatedly detected α1B, α1C, α1E, α1G , and α1H m RNAs, and additionally α1I m RNA. But α1A and α1D m essages w ere not detected. Relative expression levels of the detected Ca 2+ channel subtypes were compared by RNase protection assays. The abundance of detected m RNA m essages w as in the follow ing order: α1H α1G α1E α1B α1C α1I. These findings indicated that hum an m otile sperm express m ultiple voltage-activated Ca 2+ channel RNAs am ong which T-type and non-L-type channel m essages are likely to be predom inantly expressed. Based on their relative expression levels, w e propose that not only T-type but also non-L-type calcium channels m ay be m ajor gates for the external calcium influx, required for the acrosom e reaction.

Calcium Channels in the Development, Maturation, and Function of Spermatozoa

“…134). There is indirect evidence of their activity in human spermatozoa (47,56,276,400,418,466 Recently, recombinant proteins as well as native ZP isolated from human oocytes recovered after in vitro fertilization procedures have helped to define better the participation of Ca V channels in AR. Pharmacological studies measuring AR induced with either native ZP or recombinant ZP3 also suggest the presence and participation of Ca V channels during human AR (consult ] i is not clear, although it may involve a combination of Ca V s, SOCs, and intracellular channels in an intertwined network of signaling cascades (233,327,418,505,512).…”

Coordinated transcriptional regulation of calmegin, a testis-specific molecular chaperon, by histone deacetylase and CpG methyltransferase

“…Spermatogenesis is an essential process for mammalian reproduction and requires the precise and well-coordinated program that regulates the constantly changing patterns of gene expression (Eddy, 2002;Park et al, 2003;Wang et al, 2004). Among several key players of the process, calmegin is known as a testis-specific molecular chaperon and is crucial for binding between eggs and sperms for fertilization.…”

Effects of Raloxifene on Voltage- Dependent T-Type Ca²⁺ Channels in Mouse Spermatogenic Cells

“…Three different classes of T-type Ca 2+ channels (known as Ca V 3.1/ ␣ 1 G, Ca V 3.2/ ␣ 1 H and Ca V 3.3/ ␣ 1 I) have been cloned and expressed. Immunoconfocal microscopy has revealed that the three Ca V 3 channel isoforms are present in the mouse and human spermatogenic cells, and Ca V 3.2 is the most abundant [7] . Until recently, it had been quite difficult to electrophysiologically study sperm ion channels.…”