Actions of veratridine on tetrodotoxin‐sensitive voltage‐gated Na<sup>+</sup> currents, Na<sub>V</sub>1.6, in murine vas deferens myocytes

Zhu, Hai Lei; Wassall, Richard D.; Takai, Maki; Morinaga, Hidetaka; Nomura, Masatoshi; Cunnane, T.C.; Teramoto, Noriyoshi

doi:10.1111/j.1476-5381.2009.00301.x

Cited by 15 publications

(23 citation statements)

References 28 publications

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“…To limit the possibility of off‐target effects of veratridine, we used a concentration within the range known to activate voltage‐gated sodium channels (Zhu et al . ) and that was comparable to prior studies of veratridine‐stimulated electrogenic ion transport in mouse colon (Hyland & Cox, ). Blind assessment of the effects of CNO on preparations from GFAP ::hM3Dq and WT mice was performed, i.e.…”

Section: Methodssupporting

confidence: 88%

Enteric glial activity regulates secretomotor function in the mouse colon but does not acutely affect gut permeability

Grubišić

Gulbransen

2017

The Journal of Physiology

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Enteric glial cells are often implicated in the regulation of epithelial barrier and secretomotor functions of the intestines. But whether glial cell activity regulates these functions acutely under physiological conditions is not clear. We addressed this issue by using transgenic animal models to modify the activity of enteric glia, either reducing glial expression of connexin 43 in Sox10::CreER /Cx43 mice or activating glial calcium responses in GFAP::hM3Dq mice, and tested the effects on colonic barrier function and electrogenic ion transport in Ussing chambers. We assessed neuronal-dependent and -independent contributions by activating or inhibiting neurogenic activity with veratridine and tetrodotoxin, respectively. Our results show that the reduction of glial Cx43 expression in Sox10::CreER /Cx43 mice significantly reduced neurogenic ion transport. The selective glial activation in tissues from GFAP::hM3Dq mice evoked electrogenic ion transport to an extent equal to the direct activation of neurogenic ion transport with veratridine and glial driven responses consisted of both tetrodotoxin-sensitive and -insensitive components. The selective glial stimulation did not affect transmural ion conductance or cell-impermeant dye flux but the baseline ion conductance was more variable in Sox10::CreER /Cx43 tissues. Together, our findings show that glial activity contributes to the regulation of electrogenic ion transport in the intestine through effects on neurons and possibly direct effects on epithelial cells. However, glial activity does not appear to play a major role in the acute regulation of barrier function. These findings provide novel insight into the cellular mechanisms that control fluid transport homeostasis in the intestine.

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Section: Methodssupporting

confidence: 88%

Enteric glial activity regulates secretomotor function in the mouse colon but does not acutely affect gut permeability

Grubišić

Gulbransen

2017

The Journal of Physiology

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“…RAN (10 μM) and tetrodotoxin (0.5 μM, TTX) were alternatively used as I Na blockers, and veratridine (40 μM, VERA) was used as I NaL enhancer [12,51].…”

Section: Electrophysiologymentioning

confidence: 99%

Late sodium current (INaL) in pancreatic β-cells

Rizzetto

Rocchetti

Sala

et al. 2014

Pflugers Arch - Eur J Physiol

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Recent evidence of beneficial effects of ranolazine (RAN) in type II diabetes motivates interest in the role of the late sodium current (INaL) in glucose-stimulated insulin secretion. In the present work, we characterize INaL and its function in rat INS-1E cells and human islets cells. INaL was identified as steady-state current blocked by 10 μM RAN (IRAN) or 0.5 μM tetrodotoxin (TTX) (ITTX). Veratridine (VERA, 40 μM) was used as INaL enhancer. Baseline INaL was similar between INS-1E and human islet cells. In INS-1E cells, activated by glucose or tolbutamide, TTX or RAN hyperpolarized membrane potential (V m). VERA-induced depolarization was countered by TTX or RAN. ITTX and IRAN reversal potentials were negative to Na(+) equilibrium one, but they approached it after Na(+) substitution with Li(+) or when K(+) channels were blocked. This revealed INaL coupling with Na(+)-activated K(+) current (IKNa); expression of IKNa channels (Slick/Slack) was confirmed by transcript analysis and Western blot. RAN or TTX blunted cytosolic Ca(2+) response to depolarization. Long-term incubation in high (33 mM) glucose (CHG) constitutively enhanced INaL. VERA immediately increased glucose-stimulated insulin secretion. CHG increased glucose-independent secretion instead and abolished the secretory response to glucose. RAN or TTX countered VERA- and CHG-induced changes in insulin secretion. Our study demonstrated that (1) INaL was expressed in insulin-secreting cells and coupled to IKNa; INaL affected cytosolic Ca(2+) but, unless enhanced, barely contributed to glucose-stimulated insulin secretion (GSIS); and (2) sustained hyperglycemic stress enhanced INaL, which contributed to the attending increase of glucose-independent insulin "leak" and GSIS impairment.

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“…It has been reported that multiple types of Na V channel α‐subunits (i.e., Na V 1.6 and Na V 1.7) are expressed at the mRNA transcript and protein levels in smooth muscle cells dispersed from mouse portal vein (Saleh et al, 2005). Recently, we have investigated the molecular properties of TTX‐sensitive I Na in freshly dispersed smooth muscle cells from mouse vas deferens (Zhu et al, 2008; Zhu et al, 2009a, b). In this tissue, despite demonstrating expression of mRNA transcripts for Scn1a (Na V 1.1), Scn2a (Na V 1.2), and Scn8a (Na V 1.6), we could only demonstrate immunoreactivity for Na V 1.6 in the smooth muscle layers of vas deferens (Zhu et al, 2008).…”

mentioning

confidence: 99%

“…In this tissue, despite demonstrating expression of mRNA transcripts for Scn1a (Na V 1.1), Scn2a (Na V 1.2), and Scn8a (Na V 1.6), we could only demonstrate immunoreactivity for Na V 1.6 in the smooth muscle layers of vas deferens (Zhu et al, 2008). Furthermore, in Na V 1.6‐null mice lacking the expression of the Na V channel gene, Scn8a (Na V 1.6 −/− , Burgess et al, 1995), no I Na was detected in myocytes isolated from their vas deferens although a TTX‐sensitive I Na was recorded in their wild‐type (Na V 1.6 +/+ ) littermates (Zhu et al, 2008; Zhu et al, 2009b). These findings suggest that the α‐subunit forming Na V channels in mouse vas deferens is primarily Na V 1.6.…”

mentioning

confidence: 99%

Characterization of Na_V1.6‐mediated Na⁺ currents in smooth muscle cells isolated from mouse vas deferens

Zhu

Shibata

Inai

et al. 2010

Journal Cellular Physiology

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Patch-clamp experiments were performed to investigate the behavior of voltage-activated inward currents in vas deferens myocytes from Na V 1.6-null mice (Na V 1.6 À/À ) lacking the expression of the Na þ channel gene, Scn8a, and their wild-type littermates (Na V 1.6). Immunohistochemistry confirmed expression of Na V 1.6 in the muscle of Na V 1.6 þ/þ , but not Na V 1.6 À/À , vas deferens. PCR analysis revealed that the only b 1 -subunit gene expressed in Na V 1.6 þ/þ vas deferens was Scn1b. In Na V 1.6 þ/þ myocytes, the threshold for membrane currents evoked by 20 msec voltage ramps (À100 mV to 60 mV) was À38.5 AE 4.6 mV and this was shifted to a more positive potential (À31.2 AE 4.9 mV) by tetrodotoxin (TTX). In Na V 1.6 À/À myocytes, the threshold was À30.4 AE 3.4 mV and there was no TTX-sensitive current. The Na þ current (I Na ) in Na V 1.6 þ/þ myocytes had a bell-shaped current-voltage relationship that peaked at approximately À10 mV. Increasing the duration of the voltage ramps beyond 20 msec reduced the peak amplitude of I Na . I Na displayed both fast (t $10 msec) and slow (t $1 sec) recovery from inactivation, the magnitude of the slow component increasing with the duration of the conditioning pulse (5-40 msec). During repetitive activation (5-40 msec pulses), I Na declined at stimulation frequencies > 0.5 Hz and at 10 Hz 50% of the current remained. These findings indicate that I Na is due solely to Na V 1.6 in Na V 1.6 þ/þ myocytes. The gating properties of these channels suggest they play a major role in regulating smooth muscle excitability, particularly in response to rapid depolarizing stimuli.J. Cell. Physiol. 223: 234-243, 2010. ß 2010 Wiley-Liss, Inc.Voltage-gated Na þ channels (Na V channels) are fundamental to functioning of a wide variety of excitable cells (such as neurons, skeletal muscle fibers, and cardiac myocytes), being a prerequisite for action potential initiation and propagation. Recent molecular studies have revealed that Na V channels consist of an a-subunit and one or more b-subunit(s) (reviewed by Catterall et al., 2005). The a-subunit (250-260 kDa) alone forms functional Na þ -selective channels, containing the voltage sensor and structural elements responsible for inactivation. The b-subunits (30-40 kDa) serve a number of functions, including modulation of a-subunit function and targeting/ anchoring the channels at specific sites. To date, ten genes (Scn1a-6a, Scn8a-11a) encoding Na þ channel a-subunit proteins have been identified, and nine of those isoforms (Scn1a-5a, Scn8a-11a) have been identified as Na V channels (Na V 1.1-Na V 1.9) in cell expression systems (Catterall et al., 2005). Four isoforms of b-subunit genes (Scn1b-4b) encoding b-subunits have been identified (Catterall et al., 2005).Although tetrodotoxin (TTX)-sensitive I Na has been identified in a variety of freshly isolated vascular and visceral smooth muscle cells using patch-clamp techniques (rat portal vein, Mironneau et al., 1990; rat myometrium, Amédée et al., 1986; guinea-pig ureter, Muraki et al., 199...

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Actions of veratridine on tetrodotoxin‐sensitive voltage‐gated Na⁺ currents, Na_V1.6, in murine vas deferens myocytes

Cited by 15 publications

References 28 publications

Enteric glial activity regulates secretomotor function in the mouse colon but does not acutely affect gut permeability

Enteric glial activity regulates secretomotor function in the mouse colon but does not acutely affect gut permeability

Late sodium current (INaL) in pancreatic β-cells

Characterization of Na_V1.6‐mediated Na⁺ currents in smooth muscle cells isolated from mouse vas deferens

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Actions of veratridine on tetrodotoxin‐sensitive voltage‐gated Na+ currents, NaV1.6, in murine vas deferens myocytes

Cited by 15 publications

References 28 publications

Enteric glial activity regulates secretomotor function in the mouse colon but does not acutely affect gut permeability

Enteric glial activity regulates secretomotor function in the mouse colon but does not acutely affect gut permeability

Late sodium current (INaL) in pancreatic β-cells

Characterization of NaV1.6‐mediated Na+ currents in smooth muscle cells isolated from mouse vas deferens

Contact Info

Product

Resources

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Actions of veratridine on tetrodotoxin‐sensitive voltage‐gated Na⁺ currents, Na_V1.6, in murine vas deferens myocytes

Characterization of Na_V1.6‐mediated Na⁺ currents in smooth muscle cells isolated from mouse vas deferens