Pharmacological Targeting of Native CatSper Channels Reveals a Required Role in Maintenance of Sperm Hyperactivation |
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Authors: | Anne E Carlson Lindsey A Burnett Donato del Camino Timothy A Quill Bertil Hille Jayhong A Chong Magdalene M Moran Donner F Babcock |
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Institution: | 1. Department of Physiology and Biophysics, University of Washington, Seattle, Washington, United States of America.; 2. Hydra Biosciences Inc., Cambridge, Massachusetts, United States of America.; 3. Cecil H. and Ida Green Center for Reproductive Biology Sciences, Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.;Monash University, Australia |
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Abstract: | The four sperm-specific CatSper ion channel proteins are required for hyperactivated motility and male fertility, and for Ca2+ entry evoked by alkaline depolarization. In the absence of external Ca2+, Na+ carries current through CatSper channels in voltage-clamped sperm. Here we show that CatSper channel activity can be monitored optically with the Na+]i-reporting probe SBFI in populations of intact sperm. Removal of external Ca2+ increases SBFI signals in wild-type but not CatSper2-null sperm. The rate of the indicated rise of Na+]i is greater for sperm alkalinized with NH4Cl than for sperm acidified with propionic acid, reflecting the alkaline-promoted signature property of CatSper currents. In contrast, the Na+]i rise is slowed by candidate CatSper blocker HC-056456 (IC50 ∼3 µM). HC-056456 similarly slows the rise of Ca2+]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 does not prevent activation of motility by HCO3
− but does prevent the development of hyperactivated motility by capacitating incubations, thus producing a phenocopy of the CatSper-null sperm. When applied to hyperactivated sperm, HC-056456 causes a rapid, reversible loss of flagellar waveform asymmetry, similar to the loss that occurs when Ca2+ entry through the CatSper channel is terminated by removal of external Ca2+. Thus, open CatSper channels and entry of external Ca2+ through them sustains hyperactivated motility. These results indicate that pharmacological targeting of the CatSper channel may impose a selective late-stage block to fertility, and that high-throughput screening with an optical reporter of CatSper channel activity may identify additional selective blockers with potential for male-directed contraception. |
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