Hypoxic Conditions Promote Rhythmic Contractile Oscillations Mediated by Voltage-Gated Sodium Channels Activation in Human Arteries

Modulation of fast sodium current in airway smooth muscle cells by exchange protein directly activated by cAMP

Airway smooth muscle (ASM) cells from mouse bronchus express a fast sodium current mediated by NaV1.7. We present evidence that this current is regulated by cAMP. ASM cells were isolated by enzymatic dispersal and studied using the whole cell patch clamp technique at room temperature. A fast sodium current, INa, was observed on holding cells under voltage clamp at -100 mV and stepping to -20 mV. This current was reduced in a concentration-dependent manner by denopamine (10 and 30 µM), a β-adrenergic agonist. Forskolin (1 µM), an activator of adenylate cyclase, reduced the current by 35%, but 6-MB-cAMP (300 µM), an activator of protein kinase A (PKA), had no effect. In contrast, 8-pCPT-2-O-Me-cAMP-AM (007-AM, 10 µM), an activator of exchange protein directly activated by cAMP (Epac), reduced the current by 48%. The inhibitory effect of 007-AM was still observed in the presence of dantrolene (10 µM), an inhibitor of ryanodine receptors, and when cytosolic [Ca2+] was buffered by inclusion of 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, Sigma (BAPTA) (50 µM) in the pipette solution, suggesting that the inhibition of INa was not due to Ca2+-release from intracellular stores. When 007-AM was tested on the current-voltage relationship, it reduced the current at potentials from -30 to 0 mV, but had no effect on the steady-state activation curve. However, the steady-state inactivation V1/2, the voltage causing inactivation of 50% of the current, was shifted in the negative direction from -76.6 mV to -89.7 mV. These findings suggest that cAMP regulates INa in mouse ASM via Epac, but not PKA.NEW & NOTEWORTHY β-adrenergic agonists are commonly used in inhalers to treat asthma and chronic obstructive pulmonary disease. These work by causing bronchodilation and reducing inflammation. The present study provides evidence that these drugs have an additional action, namely, to reduce sodium influx into airway smooth muscle cells via fast voltage-dependent channels. This may have the dual effect of promoting bronchodilation and reducing remodeling of the airways, which has a detrimental effect in these diseases.

Vasomotion in human arteries and their regulations based on ion channel regulations: 10 years study

Vasomotion is the oscillation of vascular tone which gives rise to flow motion of blood into an organ. As is well known, spontaneous contractile organs such as heart, GI, and genitourinary tract produce rhythmic contraction. It imposes or removes pressure on their vessels alternatively for exchange of many substances. It was first described over 150 years ago, however the physiological mechanism and pathophysiological implications are not well understood. This study aimed to elucidate underlying mechanisms and physiological function of vasomotion in human arteries. Conventional contractile force measurement, immunohistochemistry, and Western blot analysis were employed to study human left gastric artery (HLGA) and uterine arteries (HUA). RESULTS: Circular muscle of HLGA and/or HUA produced sustained tonic contraction by high K+ (50 mM) which was blocked by 2 µM nifedipine. Stepwise stretch and high K+ produced nerve-independent spontaneous contraction (vasomotion) (around 45% of tested tissues). Vasomotion was also produced by application of BayK 8644, 5-HT, prostagrandins, oxytocin. It was blocked by nifedipine (2 µM) and blockers of intracellular Ca2+ stores. Inhibitors of Ca2+ -activated Cl- channels (DIDS and/or niflumic acid) and ATP-sensitive K+ (KATP ) channels inhibited vasomotion reversibly. Metabolic inhibition by sodium cyanide (NaCN) and several neuropeptides also regulated vasomotion in KATP channel-sensitive and -insensitive manner. Finally, we identified TMEM16A Ca2+ -activated Cl- channels and subunits of KATP channels (Kir 6.1/6.2 and sulfonylurea receptor 2B [SUR2B]), and c-Kit positivity by Western blot analysis. We conclude that vasomotion is sensitive to TMEM16A Ca2+ -activated Cl- channels and metabolic changes in human gastric and uterine arteries. Vasomotion might play an important role in the regulation of microcirculation dynamics even in pacemaker-related autonomic contractile organs in humans.

Tetrodotoxin Decreases the Contractility of Mesenteric Arteries, Revealing the Contribution of Voltage-Gated Na+ Channels in Vascular Tone Regulation

Tetrodotoxin (TTX) poisoning through the consumption of contaminated fish leads to lethal symptoms, including severe hypotension. This TTX-induced hypotension is likely due to the downfall of peripheral arterial resistance through direct or indirect effects on adrenergic signaling. TTX is a high-affinity blocker of voltage-gated Na⁺ (Na_V) channels. In arteries, Na_V channels are expressed in sympathetic nerve endings, both in the intima and media. In this present work, we aimed to decipher the role of Na_V channels in vascular tone using TTX. We first characterized the expression of Na_V channels in the aorta, a model of conduction arteries, and in mesenteric arteries (MA), a model of resistance arteries, in C57Bl/6J mice, by Western blot, immunochemistry, and absolute RT-qPCR. Our data showed that these channels are expressed in both endothelium and media of aorta and MA, in which scn2a and scn1b were the most abundant transcripts, suggesting that murine vascular Na_V channels consist of Na_V1.2 channel subtype with Na_Vβ1 auxiliary subunit. Using myography, we showed that TTX (1 µM) induced complete vasorelaxation in MA in the presence of veratridine and cocktails of antagonists (prazosin and atropine with or without suramin) that suppressed the effects of neurotransmitter release. In addition, TTX (1 µM) strongly potentiated the flow-mediated dilation response of isolated MA. Altogether, our data showed that TTX blocks Na_V channels in resistance arteries and consecutively decreases vascular tone. This could explain the drop in total peripheral resistance observed during mammal tetrodotoxications.

Effective Perturbations by Small-Molecule Modulators on Voltage-Dependent Hysteresis of Transmembrane Ionic Currents

The non-linear voltage-dependent hysteresis (Hys_(V)) of voltage-gated ionic currents can be robustly activated by the isosceles-triangular ramp voltage (V_ramp) through digital-to-analog conversion. Perturbations on this Hys_(V) behavior play a role in regulating membrane excitability in different excitable cells. A variety of small molecules may influence the strength of Hys_(V) in different types of ionic currents elicited by long-lasting triangular V_ramp. Pirfenidone, an anti-fibrotic drug, decreased the magnitude of I_h's Hys_(V) activated by triangular V_ramp, while dexmedetomidine, an agonist of α₂-adrenoceptors, effectively suppressed I_h as well as diminished the Hys_(V) strength of I_h. Oxaliplatin, a platinum-based anti-neoplastic drug, was noted to enhance the I_h's Hys_(V) strength, which is thought to be linked to the occurrence of neuropathic pain, while honokiol, a hydroxylated biphenyl compound, decreased I_h's Hys_(V). Cell exposure to lutein, a xanthophyll carotenoid, resulted in a reduction of I_h's Hys_(V) magnitude. Moreover, with cell exposure to UCL-2077, SM-102, isoplumbagin, or plumbagin, the Hys_(V) strength of erg-mediated K⁺ current activated by triangular V_ramp was effectively diminished, whereas the presence of either remdesivir or QO-58 respectively decreased or increased Hys_(V) magnitude of M-type K⁺ current. Zingerone, a methoxyphenol, was found to attenuate Hys_(V) (with low- and high-threshold loops) of L-type Ca²⁺ current induced by long-lasting triangular V_ramp. The Hys_(V) properties of persistent Na⁺ current (I_Na(P)) evoked by triangular V_ramp were characterized by a figure-of-eight (i.e., ∞) configuration with two distinct loops (i.e., low- and high-threshold loops). The presence of either tefluthrin, a pyrethroid insecticide, or t-butyl hydroperoxide, an oxidant, enhanced the Hys_(V) strength of I_Na(P). However, further addition of dapagliflozin can reverse their augmenting effects in the Hys_(V) magnitude of the current. Furthermore, the addition of esaxerenone, mirogabalin, or dapagliflozin was effective in inhibiting the strength of I_Na(P). Taken together, the observed perturbations by these small-molecule modulators on Hys_(V) strength in different types of ionic currents evoked during triangular V_ramp are expected to influence the functional activities (e.g., electrical behaviors) of different excitable cells in vitro or in vivo.

Functional expression of NaV1.7 channels in freshly dispersed mouse bronchial smooth muscle cells

Isolated smooth muscle cells (SMC) from mouse bronchus were studied using the whole-cell patch clamp technique at ~21oC. Stepping from -100 mV to -20 mV evoked inward currents of mean amplitude -275 pA. These inactivated (tau=1.1 ms) and were abolished when external Na+ was substituted with N-Methyl-D-glucamine. In current-voltage protocols, current peaked at -10 mV and reversed between +20 and +30 mV. The V1/2s of activation and inactivation were -25 & -86 mV, respectively. The current was highly sensitive to tetrodotoxin (IC50=1.5 nM) and the NaV1.7 subtype selective blocker, PF-05089771 (IC50=8.6 nM), consistent with NaV1.7 as the underlying pore-forming a subunit. Two NaV1.7-selective antibodies caused membrane-delineated staining of isolated SMC, as did a non-selective pan-NaVantibody. RT-PCR, performed on groups of ~15 isolated SMC, revealed transcripts for NaV1.7 in 7/8 samples. Veratridine (30 mM), a non-selective NaV channel activator, reduced peak current evoked by depolarization but induced a sustained current of 40 pA. Both effects were reversed by tetrodotoxin (100 nM). In tension experiments veratridine (10 mM) induced contractions that were entirely blocked by atropine (1 mM). However, in the presence of atropine, veratridine was able to modulate the pattern of activity induced by a combination of U-46619 (a thromboxane A2 mimetic) & PGE2(prostaglandin E2), by eliminating bursts in favour of sustained phasic contractions. These effects were readily reversed to control-like activity by tetrodotoxin (100 nM). In conclusion, mouse bronchial SMC functionally express NaV1.7 channels that are capable of modulating contractile activity, at least under experimental conditions.