RESUMO
Cation channel of Spermatozoa (CatSper) is one of the voltage-gated ion channels consisting of voltage sensor domains (VSDs) and pore-gate domains. CatSper is exclusively expressed in spermatozoa and indispensable for Ca2+ influx into cytosol. Recently, we have reported that the VSD of ascidian CatSper induces Ca2+-permeable pathways in heterologous expression systems. However, it is not known whether ion permeability through the VSD of CatSper is conserved in mammals. In the present study, electrophysiology and fluorometry in Xenopus oocytes revealed that Ca2+-permeable paths are also formed by expressing the VSD of murine CatSper. We also examined the permeability to monovalent cations other than Na+ in the VSD of ascidian CatSper.
Assuntos
Canais de Cálcio/metabolismo , Cálcio/metabolismo , Espermatozoides/metabolismo , Animais , Masculino , Camundongos , Xenopus laevisRESUMO
The voltage sensor domain (VSD) is a protein domain that confers sensitivity to membrane potential in voltage-gated ion channels as well as the voltage-sensing phosphatase. Although VSDs have long been considered to function as regulatory units acting on adjacent effectors, recent studies have revealed the existence of direct ion permeation paths in some mutated VSDs and in the voltage-gated proton channel. In this study, we show that calcium currents are evoked upon membrane hyperpolarization in cells expressing a VSD derived from an ascidian voltage-gated ion channel superfamily. Unlike the previously reported omega-pore in the Shaker K+ channel and rNav1.4, mutations are not required. From electrophysiological experiments in heterologous expression systems, we found that the conductance is directly mediated by the VSD itself and is carried by both monovalent and divalent cations. This is the first report of divalent cation permeation through a VSD-like structure.
Assuntos
Canais de Cálcio , Cátions Bivalentes/metabolismo , Ativação do Canal Iônico , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Animais , Canais de Cálcio/química , Canais de Cálcio/genética , Canais de Cálcio/metabolismo , Ciona intestinalis/genética , Ciona intestinalis/metabolismo , Condutividade Elétrica , Feminino , Células HEK293 , Humanos , Ativação do Canal Iônico/genética , Potenciais da Membrana/genética , Permeabilidade , Domínios Proteicos/genética , XenopusRESUMO
The voltage-gated proton channel, Hv1, is expressed in blood cells, airway epithelium, sperm and microglia, playing important roles in diverse biological contexts including phagocytosis or sperm maturation through its regulation of membrane potential and pH. The gene encoding Hv1, HVCN1, is widely found across many species and is also conserved in unicellular organisms such as algae or dinoflagellates where Hv1 plays role in calcification or bioluminescence. Voltage-gated proton channels exhibit a large variation of activation rate among different species. Here we identify an Hv1 ortholog from sea urchin, Strongylocentrotus purpuratus, SpHv1. SpHv1 retains most of key properties of Hv1 but exhibits 20-60 times more rapid activation kinetics than mammalian orthologs upon heterologous expression in HEK293T cells. Comparison between SpHv1 and mHv1 highlights novel roles of the third transmembrane segment S3 in activation gating of Hv1.
