CatSper channels in sea urchin sperm

Abstract

Sea urchin sperm swimming is regulated by speract, a decapeptide released from egg jelly that induces chemotaxis and triggers membrane potential (Em) changes, intracellular increases in cyclic nucleotides (cGMP, cAMP), pH (pH_i) and calcium concentration ([Ca²⁺]_i). The identity of the ionic transporters associated with the [Ca²⁺]_i changes required for chemotaxis is not fully known. CatSper, a sperm exclusive Ca²⁺ channel has been detected by proteomic analysis and immunofluorescence in sea urchin sperm and there is evidence for its involvement in chemotaxis. This work presents an electrophysiological characterization of a CatSper channel in sea urchin sperm. By swelling sperm suspending them in 10-fold diluted artificial sea water (ASW) we achieve on-cell patch-clamp recordings that document a mildly voltage and pH_i dependent Na⁺ permeable channel (in absence of divalent ions in the pipette), sensitive to speract, and blocked by Mibefradil (Mibe), NNC55-0396 (NNC) and RU1968 (RU) resembling CatSper. We also recorded a voltage dependent Cl^- channel inhibited by Niflumic Acid and the TMEM16A blocker.

Keywords: Calcium; CatSper; Patch-clamp; Sea urchin; Sperm.