T-type Cav3.2 Ca2+ channel is predominantly expressed in Xenopus laevis testis and involved in the fertilization process

The acrosome reaction (AR), a calcium-dependent exocytosis, is required for the mammalian fertilization process. Various ion channels, including T-type calcium channels presenting in the plasma membrane of the sperm head, play an important role in AR. In order to investigate the expression pattern and function of T-type calcium channels in Xenopus fertilization, we cloned partial cDNA sequences of cytoplasmic loops connecting domains II and III of T-type channel isoforms from the Xenopus laevis testis. The translated amino acid sequences of cloned Cav3.1 and Cav3.2 T-type channel cDNAs shared 81 and 96 % identity with those of Xenopus tropicalis, respectively. In addition, in situ hybridization showed that Cav3.1 and Cav3.2 transcripts are expressed in the testis tissues of X. laevis, with Cav3.2 transcripts more greatly expressed in testis than Cav3.1 transcripts. Pharmacological studies showed that treatment with nickel or the drug mibefradil significantly reduced the rate of fertilization in a concentration-dependent manner. Collectively, our findings suggest that Cav3.2 T-type calcium channels may play essential roles in the fertilization process of the amphibian species.