A dihydropyridine-sensitive T-type Ca²⁺ current is the main Ca²⁺ current carrier in mouse primary spermatocytes

Ca²⁺ entry through Ca²⁺ channels is likely to play an important role in the differentiation of male germ cells as well as in fertilization by mature sperm. Here we present a detailed analysis of Ca²⁺ currents expressed in acutely dissociated mouse primary spermatocytes. Patch-clamp recordings demonstrated that the only voltage-gated Ca²⁺ channels present belong to the family of T-type Ca²⁺ currents. Accordingly, Ni²⁺ (200 μM) and amiloride (500 μM/reduced current amplitude by 75 and 62%, respectively. To our knowledge, this is the first report era system where T-type Ca²⁺ channels are expressed in isolation. Unexpectedly, 5 and 10 μM nifedipine also reduced peak currents by 38 and 53%, respectively. Significant inhibition of the Ca²⁺ current occurred at concentrations as low as 2 μM. Because mature sperm cells are unable to synthesize new proteins, these Ca²⁺ channels are also likely to be present in these cells, where they may contribute to the Ca²⁺ influx required to trigger the acrosome reaction. This notion is supported by the fact that concentrations of Ni²⁺ and nifedipine, which block these Ca²⁺ currents, also inhibit the acrosome reaction. Because these channels represent the primary pathway for voltage- gated Ca²⁺ entry in mouse spermatocytes, they may also participate in regulating meiotic cell division and sperm differentiation.