Ligand-Dependent Activation of Slo Family Channels Is Defined by Interchangeable Cytosolic Domains

Xia, Xiaoming; Zhang, Xue; Lingle, Christopher J.

doi:10.1523/jneurosci.1296-04.2004

Cited by 52 publications

(73 citation statements)

References 39 publications

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“…Like the CatSper channels, mSlo3 appears specific to testis and has not been functionally expressed in mammalian cell lines. mSlo3 expression in Xenopus oocytes yielded measurable currents, and these currents were activated by intracellular alkalinization (21,22). Like I KSper , Xenopus oocyte-expressed mSlo3 is also weakly voltage-sensitive (Ϸ16 mV/e-fold), has relaxed K ϩ -selectivity, and is insensitive to [Ca 2ϩ ] i and external tetraethylammonium.…”

Section: Discussionmentioning

confidence: 99%

KSper, a pH-sensitive K ⁺ current that controls sperm membrane potential

Navarro

Kirichok

Clapham

2007

Proc. Natl. Acad. Sci. U.S.A.

198

267

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Mature mammalian spermatozoa are quiescent in the male reproductive tract. Upon ejaculation and during their transit through the female reproductive tract, they undergo changes that enable them to fertilize the egg. During this process of capacitation, they acquire progressive motility, develop hyperactivated motility, and are readied for the acrosome reaction. All of these processes are regulated by intracellular pH. In the female reproductive tract, the spermatozoan cytoplasm alkalinizes, which in turn activates a Ca 2؉ -selective current (ICatSper) required for hyperactivated motility. Here, we show that alkalinization also has a dramatic effect on membrane potential, producing a rapid hyperpolarization. This hyperpolarization is primarily mediated by a weakly outwardly rectifying K ؉ current (IKSper) originating from the principal piece of the sperm flagellum. Alkalinization activates the pH i-sensitive I KSper, setting the membrane potential to negative potentials where Ca 2؉ entry via ICatSper is maximized. IKSper is one of two dominant ion currents of capacitated sperm cells.capacitation ͉ fertilization ͉ ion channels ͉ mSlo3 ͉ reproduction B efore fertilization, mammalian sperm must undergo a poorly understood process called capacitation (1). Capacitation refers to a series of biochemical and physiological changes in the sperm cell that enable it to reach and fertilize the egg. Among these changes is an increase in the intracellular pH (pH i ) (2) and hyperpolarization of the sperm plasma membrane potential (V m ) (3, 4). Resting pH i of mammalian sperm is Ϸ6.5 as determined by pH-sensitive fluorescent probes (2, 5-7). After in vitro capacitation in bicarbonate-containing media at pH 7.4, pH i increases Ͼ0.3 units (2,8,9). When intracellular alkalinization is prevented by glucose incubation, bovine sperm fail to capacitate (8, 10).Measurements with voltage-sensitive fluorescent dyes indicate that noncapacitated murine sperm are relatively depolarized (approximately Ϫ30 mV) and hyperpolarize to approximately Ϫ60 mV during capacitation (4,11,12). Indirect measurements attribute the capacitation-associated hyperpolarization to an increase in K ϩ permeability (4) and a block of epithelial sodium channels (ENaCs) (13). Interestingly, addition of BaCl 2 (a nonspecific K ϩ channel blocker) to the capacitating medium prevented the hyperpolarization and the acrosome reaction (12). Several K ϩ channels have been reported in mammalian sperm (ref. 14; see also reviews in refs. 15 and 16), but only recently have patch-clamp methods been developed that allow whole-spermcell currents to be recorded under voltage clamp (17). To date, the inward Ca 2ϩ -selective current, I CatSper , but not outward K ϩ -selective current, has been described in detail (17, 18). By using whole-spermatozoan current clamp, we find that pH i largely determines mouse sperm membrane potential. Under whole-sperm and whole-flagellum voltage clamp, a pH i -sensitive K ϩ current (I KSper ) was identified that sets the epididymal spermatozoan membra...

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Section: Discussionmentioning

confidence: 99%

KSper, a pH-sensitive K ⁺ current that controls sperm membrane potential

Navarro

Kirichok

Clapham

2007

Proc. Natl. Acad. Sci. U.S.A.

198

267

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“…What is the molecular basis for the activation of these two channels by different intracellular signals? Studies of chimeras between SLO1 and SLO3 revealed that the specificity for Ca 2+ or pH originates solely from variations within the intracellular gating rings: channels containing a SLO1 transmembrane region and a SLO3 gating ring are alkalization-activated but Ca 2+ -insensitive, and vice versa (10). These results also showed that the allosteric regulation of SLO3 and SLO1 by pH or Ca 2+ must be similar enough to allow for the interchangeability of the gating rings.…”

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confidence: 84%

Functional and structural analysis of the human SLO3 pH- and voltage-gated K ⁺ channel

Leonetti

Yuan

Hsiung

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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The activation of eukaryotic SLO K + channels by intracellular cues, mediated by a cytoplasmic structure called the gating ring, is central to their physiological roles. SLO3 channels are exclusively expressed in mammalian sperm, where variations of intracellular pH are critical to cellular function. Previous studies primarily focused on the mouse SLO3 orthologue and revealed that, in murine sperm, SLO3 mediates a voltage-and alkalization-activated K + current essential to male fertility. Here we investigate the activation of the human SLO3 channel by intracellular pH at the functional and structural level. By using electrophysiology in a heterologous system, we show that human SLO3 opens upon intracellular pH increase and that its expression and functional properties are modulated by LRRC52, a testis-specific accessory subunit. We next present the crystal structure of the human SLO3 gating ring. Comparison with the known structures of the corresponding domain from SLO1, a Ca 2+ -activated homologue, suggests that the SLO3 gating ring structure may represent an open state. Together, these results present insights into the function of a protein expected to be critical for human reproduction and provide a framework to study the mechanism of pH gating in SLO3 channels. membrane protein | protein structure | ion channel E ukaryotic SLO1 and SLO3 channels share a unique property among the extended family of voltage-gated K + channels in that their opening requires the synergistic action of membrane depolarization and specific intracellular cues (1). This is mirrored by the distinctive architecture of SLO1 and SLO3, which includes a transmembrane voltage sensor as well as a large cytoplasmic structure called the gating ring, responsible for regulation by intracellular signals. The two homologues are closely related in amino acid sequence (42% identity between human channels), and, in fact, sequence analysis suggests that SLO3, which exists only in mammals, evolved from a duplication of the Slo1 gene, which is found across metazoans (1, 2). However, SLO1 and SLO3 diverge in one critical aspect: whereas SLO1 opens upon binding of intracellular Ca 2+ , SLO3 is activated by an increase in intracellular pH (3)(4)(5). This difference underlies fundamentally distinct physiological roles for the two channels. Whereas SLO1 is expressed in excitable cells such as neurons or muscles, where Ca 2+ entry into the cytoplasm is critical for function, SLO3 is found exclusively in sperm cells and is essential for male fertility in animal models (3,6,7). This exclusive expression pattern reflects the key importance of intracellular [H + ] signaling in the physiology of sperm, in which critical steps such as the initiation of motility or the acrosome reaction depend on intracellular alkalization (8, 9).Hence, SLO1 and SLO3 are closely related in sequence and structure but evolved to serve very divergent functions. What is the molecular basis for the activation of these two channels by different intracellular signals? Studies of chimeras ...

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“…BK channels contain a large cytosolic domain appended to the pore-forming elements of the channel (Butler et al, 1993;Xia et al, 2004). Given that the cytosolic domain of BK channels shares homology with the cytosolic domain of the MthK channel (Jiang et al, 2002a), similarities in side portal architecture and the linkage between pore and cytosolic domain may exist.…”

Section: Introductionmentioning

confidence: 99%

A Limited Access Compartment between the Pore Domain and Cytosolic Domain of the BK Channel

Zhang¹,

Zhong²,

Ding³

et al. 2006

J. Neurosci.

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Cytosolic N-terminal segments of many K ϩ channel subunits mediate rapid blockade of ion permeation by physical occlusion of the ion-conducting pore. For some channels with large cytosolic structures, access to the channel pore by inactivation domains may occur through lateral entry pathways or "side portals" that separate the pore domain and associated cytosolic structures covering the axis of the permeation pathway. However, the extent to which side portals control access of molecules to the channel or influence channel gating is unknown. Here we use removal of inactivation by trypsin as a tool to examine basic residue accessibility in both the N terminus of the native auxiliary ␤2 subunit of Ca 2ϩ -activated, BK-type K ϩ channels and ␤2 subunits with artificial inactivating N termini. The results show that, for BK channels, side portals define a protected space that precedes the channel permeation pathway and excludes small proteins such as trypsin but allows inactivation domains to enter. When channels are closed, inactivation domains readily pass through side portals, with a central antechamber preceding the permeation pathway occupied by an inactivation domain approximately half of the time under resting conditions. The restricted volume of the pathway through side portals is likely to influence kinetic properties of inactivation mechanisms, blockade by large pharmacological probes, and accessibility of modulatory factors to surfaces of the channel within the protected space.

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Ligand-Dependent Activation of Slo Family Channels Is Defined by Interchangeable Cytosolic Domains

Cited by 52 publications

References 39 publications

KSper, a pH-sensitive K ⁺ current that controls sperm membrane potential

KSper, a pH-sensitive K ⁺ current that controls sperm membrane potential

Functional and structural analysis of the human SLO3 pH- and voltage-gated K ⁺ channel

A Limited Access Compartment between the Pore Domain and Cytosolic Domain of the BK Channel

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Ligand-Dependent Activation of Slo Family Channels Is Defined by Interchangeable Cytosolic Domains

Cited by 52 publications

References 39 publications

KSper, a pH-sensitive K + current that controls sperm membrane potential

KSper, a pH-sensitive K + current that controls sperm membrane potential

Functional and structural analysis of the human SLO3 pH- and voltage-gated K + channel

A Limited Access Compartment between the Pore Domain and Cytosolic Domain of the BK Channel

Contact Info

Product

Resources

About

KSper, a pH-sensitive K ⁺ current that controls sperm membrane potential

KSper, a pH-sensitive K ⁺ current that controls sperm membrane potential

Functional and structural analysis of the human SLO3 pH- and voltage-gated K ⁺ channel