Properties of a Sodium Channel (Nax) Activated by Strong Depolarization of Xenopus Oocytes

Vasilyev, A.; Indyk, E; Rakowski, Robert F.

doi:10.1007/s00232-001-0126-x

Cited by 10 publications

(12 citation statements)

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“…In the present thesis work, this channel was demonstrated to be upregulated during apoptosis, and in previous studies it is upregulated after a prolonged depolarisation. Both our apoptotic-induced Na + currents reported here and the Na x current reported by others are blocked by a high concentration of lidocaine (reported in paper II) (Baud et al, 1982;Charpentier, 2002;Vasilyev et al, 2002). By using miRNA to suppress the Na + current upregulated during apoptosis we could identify the channel conducting the Na + current as a SCN2A ortholog.…”

Section: Discussionsupporting

confidence: 61%

“…The voltage-gated Na channel described in paper II, and which identity is revealed in paper III, is most likely responsible for causing the Na x current that has previously been described in X. laevis oocytes (Baud et al, 1982;Vasilyev et al, 2002), not to be confused with human SCN7A which also has been called Na x . The Na x current activates at positive voltages and does not inactivate.…”

Section: Discussionmentioning

confidence: 77%

“…(v) One Na channel reported in X. laevis oocytes is the Na x channel, which is blocked by TTX at high concentrations. Na x is activated by a long depolarisation to positive voltages, with the activation facilitated by insulin and mobilisation of intracellular Ca 2+ (Baud et al, 1982;Bossi et al, 1998;Charpentier and Kado, 1999;Vasilyev et al, 2002). Na x is blocked by extracellular polyvalent cations, intracellular Mg 2+ and high concentrations of the local anaesthetics lidocaine (Charpentier, 2002;Quinteiro-Blondin and Charpentier, 2001;Vasilyev et al, 2002).…”

Section: 3mentioning

confidence: 99%

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The role of ion channels and intracellular metal ions in apoptosis of Xenopus oocytes

Englund¹

2014

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Apoptosis is one type of programmed cell death, important during tissue development and to maintain the tissue homeostasis. Apoptosis comprises a complex network of internal signaling pathways, and an important part of this signaling network is the action of voltage‐gated ion channels. The aim of this thesis was to explore the role of ion channels and the role of intracellular metal ions during apoptosis in Xenopus laevis oocytes. The reasons for using these oocytes are that they are large, robust, easy to handle, and easy to study electrophysiologically. Apoptosis was induced either chemically by incubation of the oocytes in staurosporine (STS) or mechanically by centrifugation of the oocytes. Ion currents were measured by a two‐electrode voltage clamp technique, intracellular ion concentrations were measured either directly by in‐house developed K+‐selective microelectrodes or indirectly by the electrophysiological technique, and apoptosis was measured by caspase‐3 activation. Paper I describes that the intracellular K+ concentration was reduced by about 30 % during STS‐induced apoptosis. However, this reduction was prevented by excessive expression of exogenous ion channels. Despite the magnitude of the intracellular K+ concentration, either normal or reduced level, the oocytes displayed normal signs of apoptosis, suggesting that the intracellular K+ reduction was not required for the apoptotic process. Because the intracellular K+ concentration was not critical for apoptosis we searched for other ion fluxes by exploring the electrophysiological properties of X. laevis oocytes. Paper II, describes a non‐inactivating Na+ current activated at positive membrane voltages that was upregulated by a factor of five during STS‐induced apoptosis. By preventing influx of Na+, the apoptotic signaling network involving capsase‐3 was prevented. To molecularly identify this voltage‐gated Na channel, the X. tropicalis genome and conserved regions of the human SCNA genes were used as a map. Paper III, shows that the voltage‐gated Na channel corresponds to the SCN2A gene ortholog and that supression of this SCN2A ortholog using miRNA prevented cell death. In conclusion, this thesis work demonstrated that a voltage‐gated Na channel is critical for the apoptotic process in X. laevis oocytes by increasing the intracellular Na+ concentration

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Section: Discussionsupporting

confidence: 61%

Section: Discussionmentioning

confidence: 77%

Section: 3mentioning

confidence: 99%

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The role of ion channels and intracellular metal ions in apoptosis of Xenopus oocytes

Englund¹

2014

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“…Na + channels activated by ATP [37], and 4. Na x channels activated by a positive voltages [32], [38]. Even though we have not tested for intracellular acidification and NH 4 + , we found that Na x is a strong candidate for the channel described in the present investigation.…”

Section: Discussioncontrasting

confidence: 44%

A Voltage Dependent Non-Inactivating Na+ Channel Activated during Apoptosis in Xenopus Oocytes

et al. 2014

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Ion channels in the plasma membrane are important for the apoptotic process. Different types of voltage-gated ion channels are up-regulated early in the apoptotic process and block of these channels prevents or delays apoptosis. In the present investigation we examined whether ion channels are up-regulated in oocytes from the frog Xenopus laevis during apoptosis. The two-electrode voltage-clamp technique was used to record endogenous ion currents in the oocytes. During staurosporine-induced apoptosis a voltage-dependent Na+ current increased three-fold. This current was activated at voltages more positive than 0 mV (midpoint of the open-probability curve was +55 mV) and showed almost no sign of inactivation during a 1-s pulse. The current was resistant to the Na+-channel blockers tetrodotoxin (1 µM) and amiloride (10 µM), while the Ca2+-channel blocker verapamil (50 µM) in the bath solution completely blocked the current. The intracellular Na+ concentration increased in staurosporine-treated oocytes, but could be prevented by replacing extracellular Na+ whith either K+ or Choline+. Prevention of this influx of Na+ also prevented the STS-induced up-regulation of the caspase-3 activity, suggesting that the intracellular Na+ increase is required to induce apoptosis. Taken together, we have found that a voltage dependent Na+ channel is up-regulated during apoptosis and that influx of Na+ is a crucial step in the apoptotic process in Xenopus oocytes.

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“…Xenopus oocytes express several types of endogenous channels that may conduct Na ϩ (15)(16)(17)(18). To exclude the possibility that the observed increase in whole cell currents by extracellular Zn 2ϩ was due to activation of an endogenous channel, we examined the effect of 100 M ZnCl 2 on the whole cell currents in H 2 O-injected oocytes.…”

Section: External Zn 2ϩ Activates ␣␤␥ Menac Expressed In Xenopusmentioning

confidence: 99%

Extracellular Zn2+ Activates Epithelial Na+ Channels by Eliminating Na+ Self-inhibition

Sheng

Perry

Kleyman

2004

Journal of Biological Chemistry

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Inhibition of epithelial Na ؉ channel (ENaC) activity by high concentrations of extracellular Na ؉ is referred to as Na ؉ self-inhibition. We investigated the effects of external Zn 2؉ on whole cell Na ؉ currents and on the Na ؉ self-inhibition response in Xenopus oocytes expressing mouse ␣␤␥ ENaC. Na ؉ self-inhibition was examined by analyzing inward current decay from a peak current to a steady-state current following a fast switching of a low Na ؉ (1 mM) bath solution to a high Na ؉ (110 mM) solution. Our results indicate that external Zn 2؉ rapidly and reversibly activates ENaC in a dose-dependent manner with an estimated EC 50 of 2 M. External Zn 2؉ in the high Na ؉ bath also prevents or reverses Na ؉ self-inhibition with similar affinity. Zn 2؉ activation is dependent on extracellular Na ؉ concentration and is absent in ENaCs containing ␥H239 mutations that eliminate Na ؉ self-inhibition and in ␣S580C␤␥ following covalent modification by a sulfhydryl-reactive reagent that locks the channels in a fully open state. In contrast, external Ni 2؉ inhibition of ENaC currents appears to be additive to Na ؉ self-inhibition when Ni 2؉ is present in the high Na ؉ bath. Pretreatment of oocytes with Ni 2؉ in a low Na ؉ bath also prevents the current decay following a switch to a high Na ؉ bath but rendered the currents below the control steady-state level measured in the absence of Ni 2؉ pretreatment. Our results suggest that external Zn 2؉ activates ENaC by relieving the channel from Na ؉ self-inhibition, and that external Ni 2؉ mimics or masks Na ؉ self-inhibition.

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Properties of a Sodium Channel (Nax) Activated by Strong Depolarization of Xenopus Oocytes

Cited by 10 publications

References 0 publications

The role of ion channels and intracellular metal ions in apoptosis of Xenopus oocytes

The role of ion channels and intracellular metal ions in apoptosis of Xenopus oocytes

A Voltage Dependent Non-Inactivating Na+ Channel Activated during Apoptosis in Xenopus Oocytes

Extracellular Zn2+ Activates Epithelial Na+ Channels by Eliminating Na+ Self-inhibition

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