Transient receptor potential (TRPC) channels in human sperm: expression, cellular localization and involvement in the regulation of flagellar motility

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Abstract
Capacitative Ca 2+ entry is a process whereby the activation of Ca 2+ influx through the plasma membrane is triggered by depletion of intracellular Ca 2+ stores. Some transient receptor potential (TRPC) proteins have been proposed as candidates for capacitative Ca 2+ channels. Recent evidence indicates that capacitative Ca 2+ entry participates in the sperm acrosome reaction (AR), an exocytotic process necessary for fertilization. In addition, several TRPCs have been detected heterogeneously distributed in mouse sperm, suggesting that they may participate in other functions such as motility. Using reverse transcription-polymerase chain reaction (RT-PCR) analysis, RNA messengers for TRPC1, 3, 6 and 7 were found in human spermatogenic cells. Confocal indirect immunofluorescence revealed the presence of TRPC1, 3, 4 and 6 differentially localized in the human sperm, and immunogold transmission electron microscopy indicated that TRPC epitopes are mostly associated to the surface of the cells. Because all of them were detected in the flagellum, TRPC channel antagonists were tested in sperm motility using a computer-assisted assay. Our results provide what is to our knowledge the first evidence that these channels may influence human sperm motility.