Molecular identification of a hyperpolarization-activated channel in sea urchin sperm

Abstract

Sea urchin eggs attract sperm through chemotactic peptides, which evoke complex changes in membrane voltage and in the concentrations of cyclic AMP, cyclic GMP and Ca2+ ions The intracellular signalling pathways and their cellular targets are largely unknown. We have now cloned, from sea urchin testis, the complementary DNA encoding a channel polypeptide, SPIH. Functional expression of SPIH gives rise to weakly K+-selective hyperpolarization-activated channels, whose activity is enhanced by the direct action of cAMP. Thus, SPIH is under the dual control of voltage and cAMP. The SPIH channel, which is confined to the sperm flagellum, may be involved in the control of flagellar beating. SPIH currents exhibit all the hallmarks of hyperpolarization-activated currents (Ih), which participate in the rhythmic firing of central neurons, control pacemaking in the heart, and curtail saturation by bright light in retinal photoreceptors. Because of their sequence and functional properties, Ih channels form a class of their own within the superfamily of voltage-gated and cyclic-nucleotide-gated channels.

Niflumic acid disrupts marine spermatozoan chemotaxis without impairing the spatiotemporal detection of chemoattractant gradients

“…This means that the initial KCNG-mediated hyperpolarization will be within the resting V m 5240 mV and 295 mV, and needs to be enough to remove CaV channel inactivation. In this physiological V m range only a fraction of the HCN will open (Gauss et al, 1998) to promote Na + influx (the I h current) and generate the initial repolarization required to open CaV channels (however, once opened, Ca 2+ influx will further contribute to the depolarization). In rod photoreceptor cells NFA promotes a shift of the V m dependence of HCN towards more negative values (Satoh and Yamada, 2001).…”

“…Current models propose that the binding of speract to its receptor promotes the synthesis of cGMP that activate K + selective and cyclic nucleotide-gated channels (KCNG) leading to membrane potential (V m ) hyperpolarization Strünker et al, 2006;Bönigk et al, 2009). This V m change first induces a pH i increase (Nishigaki et al, 2001;Nishigaki et al, 2004), stimulates hyperpolarization-activated and cyclic nucleotide-gated channels (HCN) (Gauss et al, 1998), removes the inactivation of voltage-gated Ca 2+ channels (CaV) (Strünker et al, 2006;Granados-Gonzalez et al, 2005), and facilitates Ca 2+ extrusion by Na + /Ca 2+ exchangers (NCKX) (Jayantha Gunaratne and Vacquier, 2007;Su and Vacquier, 2002;Nishigaki et al, 2004). The opening of HCN and the influx of Na + contribute to V m depolarization, and concomitant increases in [Ca 2+ ] i and [Na + ] i further depolarize V m .…”

Abstracts of Papers at the Fifty-Sixth Annual Meeting of the Society of General Physiologists

“…HCN channels have a structure similar to that of K ϩ voltagedependent (Kv) and cyclic nucleotide-gated (CNG) channels: six transmembrane domains with an S4 segment rich in positively charged residues, which in analogy to Kv channels may act as a voltage-sensitive element, a "pore" region between S5 and S6, and a consensus sequence for binding of cyclic nucleotides at the COOH terminus. The electrophysiological properties of HCN channels expressed heterologously clearly indicate that they are the molecular determinants of native pacemaker channels in the heart and nervous system (Gauss et al, 1998;Ludwig et al, 1998Ludwig et al, , 1999Santoro et al, 1998;Ishii et al, 1999;Vaccari et al, 1999;Moroni et al, 2000).…”

“…A significant advancement in the study of the molecular properties of pacemaker channels has been obtained with the cloning of a new family of channels (hyperpolarization-activated, cyclic nucleotide gated [HCN] family: Gauss et al, 1998;Ludwig et al, 1998;Santoro et al, 1998;Vaccari et al, 1999). HCN channels have a structure similar to that of K ϩ voltagedependent (Kv) and cyclic nucleotide-gated (CNG) channels: six transmembrane domains with an S4 segment rich in positively charged residues, which in analogy to Kv channels may act as a voltage-sensitive element, a "pore" region between S5 and S6, and a consensus sequence for binding of cyclic nucleotides at the COOH terminus.…”

Local electrostatic interactions determine the diameter of fusion pores

“…If such a region is associated with the fusion pore, then the accumulation of ions (at the cytoplasmic or extracellular side) could affect the stability and local curvature of the pore, as proposed by Kabaso et al 18 Recently, we reported that Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels modulate fusion pore properties. 19 HCN channels are permeable to cations (Na C , K C and Ca 2C ) [20][21][22] and likely affect exocytosis indirectly by increasing the local [Ca 2C ] i , but may also contribute directly via electrostatic interactions with charged membrane constituents near the fusion pore. Here, we assessed the contribution of electrostatic interactions, mediated by extracellular diand trivalent cations, to changes in fusion pore conductance, a parameter reporting pore geometry and in particular fusion pore diameter.…”