DGNAC1, A GONAD-SPECIFIC AMILORIDE-SENSITIVE NA+ CHANNEL

Amiloride-sensitive sodium channels have been implicated in reproducti ve and early developmental processes of several species. These include the fast block of polyspermy in Xenopus oocytes that follows the sper m binding to the egg or blastocoel expansion in mammalian embryo. We h ave now identified a gene called dGNaC1 that is specifically expressed in the gonads and early embryo in Drosophila melanogaster. The corres ponding protein belongs to the superfamily of cationic channels blocke d by amiloride that includes Caenorhabditis elegans degenerins, the He lix aspersa FMRF-amide ionotropic receptor (FaNaC), the mammalian epit helial Na+ channel (ENaC), and acid-sensing ionic channels (ASIC, DRAS IC, and MDEG). Expression of dGNaC1 in Xenopus oocytes generates a con stitutive current that does not discriminate between Na+ and Li+, but is selective for Na+ over K+. This current is blocked by amiloride (IC 50 = 24 mu M), benzamil (IC50 = 2 mu M), and ethylisopropyl amiloride (IC50 = 49 mu M). These properties are clearly different from those ob tained after expression of the previously cloned members of this famil y, including ENaC and the human alpha ENaC-like subunit, delta NaC. In terestingly, the pharmacology of dGNaC1 is not very different from tha t found for the Na+ channel characterized in rabbit preimplantation em bryos. We postulate that this channel may participate in gametogenesis and early embryonic development in Drosophila.