CatSper

HC-056456 similarly slows the rise of [Ca ²⁺ ] _i that is evoked by alkaline depolarization and reported by fura-2. HC-056456 also selectively and reversibly decreased CatSper currents recorded from patch-clamped sperm. HC-056456 produces a pharmacological phenocopy of the CatSper-null sperm. Acute application of HC-056456 causes rapid loss of flagellar waveform asymmetry from hyperactivated sperm, indicating that continued entry of Ca ²⁺ through CatSper channels is required to maintain hyperactivation. HC-056456 selectively and reversibly blocks CatSper currents. The specificity and reversibility of the blockade of CatSper-dependent currents by HC-056456 is examined by using patch clamp recordings. The observed current is blocked slightly more than 50% by 20 μM HC-056456 (estimated IC ₅₀ near 15 μM). In concept, it remains possible that CatSper channel heterogeneity explains residual HC-056456-resistant current. The action of HC-056456 on KSper channels, the other major cation channel observed in patch-clamped sperm, is also examined. Subsequent application of 50 μM HC-056456 results in partial blockade of this current. For HC-056456 action on KSper an IC ₅₀ near 40 μM is estimated.