Activation of mouse Otop3 proton channels by Zn2.

Otopetrins (Otop1-Otop3) belong to a newly identified family of proton (H+) channels activated by extracellular acidification. Here, we found that Zn2+ activates the mouse Otop3 (mOtop3) proton channels by using electrophysiological patch-clamp techniques. In mOtop3-expressing human embryonic kidney HEK293T cells, a biphasic inward mOtop3 H+ current comprising a fast transient current followed by a sustained current was observed upon extracellular acidification at pH 5.0. No significant activation of the mOtop3 channel was observed at pH 6.5 and 7.4, but interestingly, Zn2+ dose-dependently induced a sustained activation of mOtop3 under these pH conditions. Increasing the Zn2+ concentration had no effect on the reversal potential of the channel currents, suggesting that Zn2+ does not permeate through the mOtop3. The activation of the mOtop3 channel was specific to Zn2+ among divalent metal cations. Our findings reveal a novel modulatory mechanism of mOtop3 proton channels by Zn2+.

Giant Density of States Enhancement Driven by a Zero-Mode Landau Level in Semimetallic Black Phosphorus under Pressure.

Dirac fermion systems form a unique Landau level at the Fermi level-the so-called zero mode-whose observation itself will provide strong evidence of the presence of Dirac dispersions. Here, we report the study of semimetallic black phosphorus under pressure by ^{31}P-nuclear magnetic resonance measurements in a wide range of magnetic field up to 24.0 T. We have found a field-induced giant enhancement of 1/T_{1}T, where 1/T_{1} is the nuclear spin lattice relaxation rate: 1/T_{1}T at 24.0 T reaches more than 20 times larger than that at 2.0 T. The increase in 1/T_{1}T above 6.5 T is approximately proportional to the squared field, implying a linear relationship between the density of states and the field. We also found that, while 1/T_{1}T at a constant field is independent of temperature in the low-temperature region, it steeply increases with temperature above 100 K. All these phenomena are well explained by considering the effect of Landau quantization on three-dimensional Dirac fermions. The present study demonstrates that 1/T_{1} is an excellent quantity to probe the zero-mode Landau level and to identify the dimensionality of the Dirac fermion system.

Cardiac glycosides stimulate endocytosis of GLUT1 via intracellular Na+ ,K+ -ATPase α3-isoform in human cancer cells.

Glucose transporter GLUT1 plays a primary role in the glucose metabolism of cancer cells. Here, we found that cardiac glycosides (CGs) such as ouabain, oleandrin, and digoxin, which are Na+ ,K+ -ATPase inhibitors, decreased the GLUT1 expression in the plasma membrane of human cancer cells (liver cancer HepG2, colon cancer HT-29, gastric cancer MKN45, and oral cancer KB cells). The effective concentration of ouabain was lower than that for inhibiting the activity of Na+ ,K+ -ATPase α1-isoform (α1NaK) in the plasma membrane. The CGs also inhibited [3 H]2-deoxy- d-glucose uptake, lactate secretion, and proliferation of the cancer cells. In intracellular vesicles of human cancer cells, Na+ ,K+ -ATPase α3-isoform (α3NaK) is abnormally expressed. Here, a low concentration of ouabain inhibited the activity of α3NaK. Knockdown of α3NaK significantly inhibited the ouabain-decreased GLUT1 expression in HepG2 cells, while the α1NaK knockdown did not. Consistent with the results in human cancer cells, CGs had no effect on GLUT1 expression in rat liver cancer dRLh-84 cells where α3NaK was not endogenously expressed. Interestingly, CGs decreased GLUT expression in the dRLh-84 cells exogenously expressing α3NaK. In HepG2 cells, α3NaK was found to be colocalized with TPC1, a Ca2+ -releasing channel activated by nicotinic acid adenine dinucleotide phosphate (NAADP). The CGs-decreased GLUT1 expression was significantly inhibited by a Ca2+ chelator, a Ca2+ -ATPase inhibitor, and a NAADP antagonist. The GLUT1 decrease was also attenuated by inhibitors of dynamin and phosphatidylinositol-3 kinases (PI3Ks). In conclusion, the binding of CGs to intracellular α3NaK elicits the NAADP-mediated Ca2+ mobilization followed by the dynamin-dependent GLUT1 endocytosis in human cancer cells.

Inhibition of gastric H+,K+-ATPase by new dihydropyrazole derivative KYY-008.

The gastric proton pump (H+,K+-ATPase) responsible for the H+ secretion of gastric acid is an essential therapeutic target for acid-related diseases. H+,K+-ATPase belongs to a P2-type ATPase family. Here, we examined the effects of a newly synthesized dihydropyrazole derivative KYY-008 on the H+,K+-ATPase. KYY-008 concentration-dependently inhibited the enzyme activity of the ATPase in the membrane fractions prepared from isolated hog gastric mucosa and from human kidney HEK293 cells in which gastric H+,K+-ATPase is exogenously expressed. The IC50 values in these samples were 3.4 µM and 3.7 µM, respectively. In addition, KYY-008 significantly inhibited the H+,K+-ATPase-derived H+ uptake into the tightly sealed vesicles prepared from the hog gastric mucosa. In contrast, KYY-008 has no effect on the activities of other P2-type ATPases such as Na+,K+-ATPase and Ca2+-ATPase. KYY-008 did not change the ionic currents of voltage-dependent Ca2+ channels, that were potential targets for some dihydropyrazole derivatives. Together, we discovered a new dihydropyrazole derivative which acts as a selective inhibitor of gastric H+,K+-ATPase.

Impaired actin filaments decrease cisplatin sensitivity via dysfunction of volume-sensitive Cl- channels in human epidermoid carcinoma cells.

Cisplatin is a widely used platinum-based anticancer drug in the chemotherapy of numerous human cancers. However, cancer cells acquire resistance to cisplatin. So far, functional loss of volume-sensitive outwardly rectifying (VSOR) Cl- channels has been reported to contribute to cisplatin resistance of cancer cells. Here, we analyzed protein expression patterns of human epidermoid carcinoma KB cells and its cisplatin-resistant KCP-4 cells. Intriguingly, KB cells exhibited higher ß-actin expression and clearer actin filaments than KCP-4 cells. The ß-actin knockdown in KB cells decreased VSOR Cl- currents and inhibited the regulatory volume decrease (RVD) process after cell swelling. Consistently, KB cells treated with cytochalasin D, which depolymerizes actin filaments, showed smaller VSOR Cl- currents and slower RVD. Cytochalasin D also inhibited cisplatin-triggered apoptosis in KB cells. These results suggest that the disruption of actin filaments cause the dysfunction of VSOR Cl- channels, which elicits resistance to cisplatin in human epidermoid carcinoma cells.

Non-morphogenic effect of Sonic Hedgehog on gastric H+,K+-ATPase activity.

In the stomach, Sonic Hedgehog (Shh) is highly expressed in gastric parietal cells, and acts as a morphogen in early development of the organ. Here, we found that the cleaved N-terminal fragment of Shh (Shh-N) was abundantly expressed in hog gastric vesicles derived from the apical membrane of parietal cells. Interestingly, Shh-N recombinant significantly decreased K+-dependent ATP-hydrolyzing activity, which is sensitive to an inhibitor of H+,K+-ATPase (SCH28080), in hog gastric tubulovesicles and membrane fractions of the H+,K+-ATPase-expressing cells. In the living cells, Shh-N recombinant inhibited the SCH28080-sensitive 86Rb+-uptake. Together, Shh-N may directly bind to extracellular side of H+,K+-ATPase, and negatively regulates the pump activity. This is the first report to explore non-morphogenic property of Shh on ion transporters.

Cardiorespiratory Responses to Pool Floor Walking in People Poststroke.

OBJECTIVE: To compare cardiorespiratory responses between pool floor walking and overground walking (OW) in people poststroke. DESIGN: Cross-sectional study. SETTING: University-based therapeutic exercise facility. PARTICIPANTS: Participants (N=28) were comprised of 14 community-dwelling individuals poststroke (5.57±3.57y poststroke) and 14 age- and sex-matched healthy adults (mean age, 58.00±15.51y; male/female ratio, 9:5). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: A telemetric metabolic system was used to collect cardiorespiratory variables, including oxygen consumption (V˙o2), energy expenditure (EE), and expired volume per unit time (V˙e), during 6-minute walking sessions in chest-depth water and on land at a matched speed, determined by average of maximum walking speed in water. RESULTS: Individuals poststroke elicited no significant differences in cardiorespiratory responses between pool floor walking and OW. However, healthy controls showed significant increases in mean V˙o2 values by 94%, EE values by 109%, and V˙e values by 94% (all P<.05) during pool floor walking compared with OW. A 2×2 mixed model analysis of variance revealed a significant group × condition interaction in V˙o2, in which the control group increased V˙o2 from OW to pool floor walking, whereas the stroke group did not. CONCLUSIONS: Our results indicate that people poststroke, unlike healthy adults, do not increase EE while walking in water compared with on land. Unlike stationary walking on an aquatic treadmill, forward locomotion during pool floor walking at faster speeds may have increased drag force, which requires greater EE from healthy adults. Without demanding excessive EE, walking in water may offer a naturally supportive environment for gait training in the early stages of rehabilitation.

Inhibition of Gastric H+,K+-ATPase Activity in Vitro by Dissolution Media of Original Brand-Name and Generic Tablets of Lansoprazole, a Proton Pump Inhibitor.

To investigate the inhibitory effect of a commercial proton pump inhibitor (lansoprazole) on the gastric proton pump H+,K+-ATPase in vitro, we used orally disintegrating (OD) tablets including original brand-name and generic tablets. In the course of the development of generic products, dissolution and clinical tests are necessary to ensure their bioequivalence to the original brand-name products; by contrast, there is almost no opportunity to demonstrate their activity in vitro. This study initially compared the similarity of the dissolution of test generic tablets with that of the original brand-name tablets. The dissolution tests for 15 and 30-mg lansoprazole tablets found their dissolution properties were similar. Subsequently, the dissolution media were sampled and then their effects on the H+,K+-ATPase activity were measured using tubulovesicles prepared from the gastric mucosa of hogs. We confirmed that the inhibitory effects of the generic tablets on H+,K+-ATPase activity were consistent with those of the original brand-name tablets. Furthermore, lansoprazole contents in each tablet estimated from their inhibitory effects were in good agreement with their active pharmaceutical ingredient content. To our knowledge, this is the first technical report to compare the in vitro biochemical activity of lansoprazole OD tablets between the original brand-name and generic commercial products.

Positive regulation of the enzymatic activity of gastric H(+),K(+)-ATPase by sialylation of its ß-subunit.

The gastric proton pump (H(+),K(+)-ATPase) consists of a catalytic α-subunit (αHK) and a glycosylated ß-subunit (ßHK). ßHK glycosylation is essential for the apical trafficking and stability of αHK in gastric parietal cells. Here, we report the properties of sialic acids at the termini of the oligosaccharide chains of ßHK. Sialylation of ßHK was found in LLC-PK1 cells stably expressing αHK and ßHK by staining of the cells with lectin-tagged fluorescent polymeric nanoparticles. This sialylation was also confirmed by biochemical studies using sialic acid-binding lectin beads and an anti-ßHK antibody. The sialic acids of ßHK are cleaved enzymatically by neuraminidase (sialidase) and nonenzymatically by an acidic solution (pH5). Interestingly, the enzymatic activity of H(+),K(+)-ATPase was significantly decreased by cleavage of the sialic acids of ßHK. In contrast, ßHK was not sialylated in the gastric tubulovesicles prepared from the stomach of fed hogs. The H(+),K(+)-ATPase activity in these tubulovesicles was not significantly altered by neuraminidase. Importantly, the sialylation of ßHK was observed in the gastric samples prepared from the stomach of famotidine (a histamine H2 receptor antagonist)-treated rats, but not histamine (an acid secretagogue)-treated rats. The enzymatic activity of H(+),K(+)-ATPase in the samples of the famotidine-treated rats was significantly higher than in the histamine-treated rats. The effects of famotidine were weakened by neuraminidase. These results indicate that ßHK is sialylated at neutral or weakly acidic pH, but not at acidic pH, suggesting that the sialic acids of ßHK positively regulate the enzymatic activity of αHK.

Functional complexes of the proton pump and chloride transporter in gastric acid secretion.

Proton(H+) of gastric acid(HCl) is actively secreted by gastric proton pump (H+, K+- ATPase) in the parietal cells. The proton pump is expressed in both tubulovesicles and apical membrane of the cells. In resting parietal cells, tubulovesicles are present in intracellular compartments underlying the apical membrane and forming a reticulated meshwork. Upon stimulation, tubulovesicles fuse each other and connect with the apical membrane, resulting in massive acid secretion. On the other hand, the mechanism of apical Cl- transport for HCl secretion is not fully understood, although several Cl- transporters and Cl- channels have been reported to be the candidate. Here, we summarized the function of Cl- transporters such as KCC4, a K+-Cl- cotransporter, and ClC-5, a Cl-/H+ exchanger, in gastric acid secretion.

Gating modulation by heat of the polycystin transient receptor potential channel PKD2L1 (TRPP3).

Polycystic kidney disease 2-like 1 (PKD2L1), previously called transient receptor potential polycystin 3 (TRPP3), forms a voltage-dependent nonselective cation channel that exhibits large tail currents triggered by repolarization after depolarization. Since it has previously been proposed that temperature sensitivity of some TRP channels is linked to the voltage-dependent gating, we here investigated heating effects on PKD2L1 currents in human embryonic kidney HEK293T cells overexpressing mouse PKD2L1. Tail PKD2L1 currents were increased by heating to 32 °C, but decreased at more than 36 °C. Voltage dependency of the PKD2L1 channel was shifted by heating in a bimodal fashion: an increase in temperature to 32 °C and to 36 °C shifted the activation curves toward the left and the right, respectively. In addition, heating accelerated deactivation of tail PKD2L1 currents. To analyze the channel gating kinetics, single-channel events of the PKD2L1 channel were recorded at hyperpolarized potentials under whole-cell configurations. A rise in temperature decreased the open probability of the channel. Dwell-time analysis showed that both open and closed dwell times during heating were shorter than those at room temperature. Interestingly, a rapid temperature drop after heating markedly enhanced the PKD2L1 currents at both single-channel and whole-cell levels. The rebound activation of the PKD2L1 channel was due to an increase in the open probability but not in the single-channel conductance. These results suggest that heating opens but subsequently inactivates PKD2L1 channels, which is essential for the rebound activation of the channel after heating.

Up-regulation of Kv7.1 channels in thromboxane A2-induced colonic cancer cell proliferation.

Thromboxane A2 (TXA2) is known to stimulate colonic cancer cell proliferation, although the mechanism has not been clarified. In this study, we compared the expression levels of Kv7.1 K(+) channels between human colorectal cancer tissue and the accompanying non-tumor mucosa. Kv7.1 proteins were found to be consistently up-regulated in the cancer tissues from different patients. Kv7.1 was also expressed in human colonic cancer cell lines. Treatment of colonic cancer cells with 9,11-epithio-11,12-methano-thromboxane A2 (STA2), a stable analogue of TXA2, significantly increased whole-cell K(+) currents sensitive to chromanol 293B, an inhibitor of Kv7.1 channels, in parallel with an increased expression of Kv7.1 proteins. In contrast, TXB2, an inactive metabolite of TXA2, had no effects on expression level and function of Kv7.1. A TXA2 receptor antagonist (SQ29548) and an inhibitor of cAMP-dependent protein kinase (Rp-8-Br-MB-cAMPS) inhibited STA2-induced increases in both Kv7.1 expression and chromanol 293B-sensitive K(+) currents. Interestingly, STA2-stimulated proliferation of colonic cancer cells was inhibited by chromanol 293B. These results suggest that Kv7.1 channels are involved in the TXA2-induced cancer cell proliferation and that they are up-regulated by the TXA2 receptor-mediated cAMP pathway.

Negative regulation of thyroid adenoma-associated protein (THADA) in the cardiac glycoside-induced anti-cancer effect.

Cardiac glycosides, known as inhibitors of Na+,K+-ATPase, have anti-cancer effects such as suppression of cancer cell proliferation and induction of cancer cell death. Here, we examined the signaling pathway elicited by cardiac glycosides in the human hepatocellular carcinoma HepG2 cells and human epidermoid carcinoma KB cells. Three kinds of cardiac glycosides (ouabain, oleandrin, and digoxin) inhibited the cancer cell proliferation and decreased the expression level of thyroid adenoma-associated protein (THADA). Interestingly, the knockdown of THADA inhibited cancer cell proliferation, and the proliferation was significantly rescued by re-expression of THADA in the THADA-knockdown cells. In addition, the THADA-knockdown markedly decreased the expression level of L-type amino acid transporter LAT1. Cardiac glycosides also reduced the LAT1 expression. The LAT1 inhibitor, JPH203, significantly weakened the cancer cell proliferation. These results suggest that the binding of cardiac glycosides to Na+,K+-ATPase negatively regulates the THADA-LAT1 pathway, exerting the anti-proliferative effect in cancer cells.

TMEM16F is a component of a Ca2+-activated Cl- channel but not a volume-sensitive outwardly rectifying Cl- channel.

TMEM16 (transmembrane protein 16) proteins, which possess eight putative transmembrane domains with intracellular NH2- and COOH-terminal tails, are thought to comprise a Cl(-) channel family. The function of TMEM16F, a member of the TMEM16 family, has been greatly controversial. In the present study, we performed whole cell patch-clamp recordings to investigate the function of human TMEM16F. In TMEM16F-transfected HEK293T cells but not TMEM16K- and mock-transfected cells, activation of membrane currents with strong outward rectification was found to be induced by application of a Ca(2+) ionophore, ionomycin, or by an increase in the intracellular free Ca(2+) concentration. The free Ca(2+) concentration for half-maximal activation of TMEM16F currents was 9.6 µM, which is distinctly higher than that for TMEM16A/B currents. The outwardly rectifying current-voltage relationship for TMEM16F currents was not changed by an increase in the intracellular Ca(2+) level, in contrast to TMEM16A/B currents. The Ca(2+)-activated TMEM16F currents were anion selective, because replacing Cl(-) with aspartate(-) in the bathing solution without changing cation concentrations caused a positive shift of the reversal potential. The anion selectivity sequence of the TMEM16F channel was I(-) > Br(-) > Cl(-) > F(-) > aspartate(-). Niflumic acid, a Ca(2+)-activated Cl(-) channel blocker, inhibited the TMEM16F-dependent Cl(-) currents. Neither overexpression nor knockdown of TMEM16F affected volume-sensitive outwardly rectifying Cl(-) channel (VSOR) currents activated by osmotic swelling or apoptotic stimulation. These results demonstrate that human TMEM16F is an essential component of a Ca(2+)-activated Cl(-) channel with a Ca(2+) sensitivity that is distinct from that of TMEM16A/B and that it is not related to VSOR activity.

[Novel pathophysiological functions of Na+,K+-ATPases and Cl- channels in cancer cells].

Na+,K+-ATPases are essential for maintaining the membrane potential in almost all cells, and their catalytic subunits have four isoforms (α1-α4). Volume-regulated anion channel (VRAC) plays an important role in the cell death signaling pathway in addition to its fundamental role in cell volume maintenance. First, we introduce that disruption of actin filaments cause the dysfunction of VRAC, which elicits resistance to cisplatin in the cancer cells. Next, we summarize the cardiac glycosides-induced signaling pathway mediated by the crosstalk between Na+,K+-ATPase α1-isoform (α1NaK) and VRAC in the membrane microdomain of the cancer cells. In this mechanism, sub-micromolar concentrations of cardiac glycosides bind to the receptor-type α1NaK, and generate VRAC activities concomitantly with a deceleration of cancer cell proliferation. Finally, we summarize the pathophysiological function of α3NaK, which is abnormally expressed in the intracellular vesicles of cancer cells. The cancer cell can survive even under loss of anchorage because they have the avoidance mechanism for anoikis. On cancer cell detachment, we found that intracellular α3NaK is translocated to the plasma membrane and this event contributes to the survival of the cells. Interestingly, cardiac glycosides inhibited the α3NaK translocation and cell survival. Our findings may open up new opportunities for the development of cancer medicines.

Parkinson's disease-associated ATP13A2/PARK9 functions as a lysosomal H+,K+-ATPase.

Mutations in the human ATP13A2 (PARK9), a lysosomal ATPase, cause Kufor-Rakeb Syndrome, an early-onset form of Parkinson's disease (PD). Here, we demonstrate that ATP13A2 functions as a lysosomal H+,K+-ATPase. The K+-dependent ATPase activity and the lysosomal K+-transport activity of ATP13A2 are inhibited by an inhibitor of sarco/endoplasmic reticulum Ca2+-ATPase, thapsigargin, and K+-competitive inhibitors of gastric H+,K+-ATPase, such as vonoprazan and SCH28080. Interestingly, these H+,K+-ATPase inhibitors cause lysosomal alkalinization and α-synuclein accumulation, which are pathological hallmarks of PD. Furthermore, PD-associated mutants of ATP13A2 show abnormal expression and function. Our results suggest that the H+/K+-transporting function of ATP13A2 contributes to acidification and α-synuclein degradation in lysosomes.

Polycystic kidney disease 2-like 1 channel contributes to the bitter aftertaste perception of quinine.

Bitterness is an important physiological function in the defense responses to avoid toxic foods. The taste receptor 2 family is well known to mediate bitter taste perception in Type II taste cells. Here, we report that the polycystic kidney disease 2-like 1 (PKD2L1) channel is a novel sensor for the bitter aftertaste in Type III taste cells. The PKD2L1 channel showed rebound activation after the washout of quinine, a bitter tastant, in electrophysiological whole-cell recordings of the PKD2L1-expressing HEK293T cells and Ca2+-imaging analysis of Type III taste cells isolated from wild-type PKD2L1 mice. In the short-term two-bottle preference and lick tests in vivo, the wild-type mice avoided normal water while the PKD2L1-knockout mice preferred normal water after they ingested the quinine-containing water. These results may explain the new mechanism of the quinine-triggered bitter aftertaste perception in Type III taste cells.

Role of cholesterol in functional association between K(+)-Cl(-) cotransporter-3a and Na+,K(+)-ATPase.

K(+)-Cl(-) cotransporter-3a (KCC3a) is associated with Na(+),K(+)-ATPase α1-subunit (α1NaK) in lipid rafts of gastric acid-secreting cells and positively regulates Na(+),K(+)-ATPase activity. Here, effects of cholesterol on association of KCC3a with α1NaK in lipid rafts were studied in LLC-PK1 cells stably expressing KCC3a. In the cells, lipid rafts destructed by methyl-ß-cyclodextrin (MßCD) could be reconstructed by exogenous addition of cholesterol accompanying a shift of both KCC3a and α1NaK from non-rafts to rafts. The KCC3a-increased Na(+),K(+)-ATPase activity was abolished by MßCD, and recovered by repletion of cholesterol without changing expression levels of KCC3a and α1NaK in the cells. KCC3a was co-immunoprecipitated with α1NaK even after destruction of lipid rafts by MßCD, indicating that molecular association of KCC3a with α1NaK still retains in the non-raft environment. Our results suggest that cholesterol is essential for eliciting up-regulation of Na(+),K(+)-ATPase activity by KCC3a in the KCC3a-α1NaK complex.

Protective effects of volatile components of aged garlic extract against ultraviolet B-induced apoptosis in human skin fibroblasts.

Aged garlic extract (AGE) has been shown to protect the skin against UV-induced damage, but effects of its volatile components remain unknown. We investigated the effects of the volatile fraction of AGE on the responses of cultured skin fibroblasts subjected to UV-B irradiation. UV-B irradiation (20 mJ/cm2 ) reduced the cell viability to 55% of control. The nonvolatile and volatile fractions of AGE inhibited the UV-B-induced reduction of cell viability; the cell viabilities were 100% and 73%, respectively. The volatile fraction inhibited the UV-B-induced increase in apoptotic cell death by 28%. The volatile fraction also inhibited the phosphorylation of mitogen-activated protein kinases (MAPKs) induced by UV-B irradiation. GC-MS analysis revealed that a large number of volatile compounds were generated during aging of garlic. These results suggest that the volatile fraction of AGE has protective effects against the UV-B-induced death of skin fibroblasts, and that this effect may partly be due to an inhibition of apoptosis via the downregulation of MAPK signaling. The volatile compounds of AGE may have beneficial applications for skin health. PRACTICAL APPLICATIONS: In this study, we investigated the effects of AGE against cell damage of UV-B-irradiated human skin fibroblasts. The aging process of garlic produced characteristic volatile compounds that have significant protective effects against UV-induced cell damage. Our results demonstrated that the aging process is a suitable method to develop added value in garlic extracts to improve skin health.

Regulation of TRPV1 channel activities by intracellular ATP in the absence of capsaicin.

Transient receptor potential vanilloid 1 (TRPV1) is a voltage-dependent non-selective cation channel activated by capsaicin, the main pungent ingredient of chili peppers, and noxious heat. Although TRPV1 channels produce outwardly rectifying currents even in the absence of capsaicin, little is known about the regulation mechanism of the TRPV1 currents. In the present study, we found that intracellular ATP regulates the basal activities of TRPV1 channels in a concentration-dependent manner. The ATP-dependent regulation of TRPV1 channels was mediated by phosphoinositides. Moreover, an increase in intracellular ATP concentration negatively shifted voltage-dependent activation of TRPV1 channels. These results suggest that the ATP-dependent production of phosphoinositides regulates the voltage-dependent gating of the basal TRPV1 channel activities in the absence of capsaicin.