Reduced molecular expression of K(+) channel proteins in vascular smooth muscle from rats made hypertensive with N{omega}-nitro-L-arginine

Smooth muscle membrane potential (E(m)) depends on K(+) channels, and arteries from rats made hypertensive with N(omega)-nitro-l-arginine (LHR) are depolarized compared with control. We hypothesized that decreased K(+) channel function, due to decreased K(+) channel protein expression, underlies E(m) depolarization. Furthermore, K(+) channel blockers should move control E(m) (-46 +/- 1 mV) toward that in LHR (-37 +/- 2 mV) and normalize contraction. The E(m) vs. K(+) relationship was less steep in LHR (23 +/- 2 vs. 28 +/- 1 mV/log K(+) concentration), and contractile sensitivity to K(+) was increased (EC(50) = 37 +/- 1 vs. 23 +/- 1 mM). Iberiotoxin (10 nM), an inhibitor of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels, depolarized control and LHR E(m) to -35 +/- 1 and -30 +/- 2 mV, respectively; however, effects on K(+) sensitivity were more profound in LHR (EC(50) = 25 +/- 2 vs. 15 +/- 3 mM). The voltage-dependent K(+) (K(V)) channel blocker 4-aminopyridine (3 mM) depolarized control E(m) to the level of LHR (-28 +/- 1 vs. -28 +/- 1 mV); however, effects on K(+) sensitivity were greater in LHR (EC(50) = 17 +/- 4 vs. 4 +/- 4 mM). Western blots revealed reduced BK(Ca) and K(V)1.5 channel expression in LHR arteries. The findings suggest that diminished expression of K(+) channels contributes to depolarization and enhanced contractile sensitivity. These conclusions are supported by direct electrophysiological assessment of BK(Ca) and K(V) channel function in control and LHR smooth muscle cells.     

Evidence for KCNQ1 K+ channel expression in rat zymogen granule membranes and involvement in cholecystokinin-induced pancreatic acinar secretion

Secretion of enzymes and fluid induced by Ca(2+) in pancreatic acini is not completely understood and may involve activation of ion conductive pathways in zymogen granule (ZG) membranes. We hypothesized that a chromanol 293B-sensitive K(+) conductance carried by a KCNQ1 protein is expressed in ZG membranes (ZGM). In suspensions of rat pancreatic ZG, ion flux was determined by ionophore-induced osmotic lysis of ZG suspended in isotonic salts. The KCNQ1 blocker 293B selectively blocked K(+) permeability (IC(50) of approximately 10 microM). After incorporation of ZGM into planar bilayer membranes, cation channels were detected in 645/150 mM potassium gluconate cis/trans solutions. Channels had linear current-voltage relationships, a reversal potential (E(rev)) of -20.9 +/- 0.9 mV, and a single-channel K(+) conductance (g(K)) of 265.8 +/- 44.0 pS (n = 39). Replacement of cis 500 mM K(+) by 500 mM Na(+) shifted E(rev) to -2.4 +/- 3.6 mV (n = 3), indicating K(+) selectivity. Single-channel analysis identified several K(+) channel groups with distinct channel behaviors. K(+) channels with a g(K) of 651.8 +/- 88.0 pS, E(rev) of -22.9 +/- 2.2 mV, and open probability (P(open)) of 0.43 +/- 0.06 at 0 mV (n = 6) and channels with a g(K) of 155.0 +/- 11.4 pS, E(rev) of -18.3 +/- 1.8 mV, and P(open) of 0.80 +/- 0.03 at 0 mV (n = 3) were inhibited by 100 microM 293B or by the more selective inhibitor HMR-1556 but not by the maxi-Ca(2+)-activated K(+) channel (BK channel) inhibitor charybdotoxin (5 nM). KCNQ1 protein was demonstrated by immunoperoxidase labeling of pancreatic tissue, immunogold labeling of ZG, and immunoblotting of ZGM. 293B also inhibited cholecystokinin-induced amylase secretion of permeabilized acini (IC(50) of approximately 10 microM). Thus KCNQ1 may account for ZG K(+) conductance and contribute to pancreatic hormone-stimulated enzyme and fluid secretion.     

KDC1, a novel carrot root hair K+ channel. Cloning, characterization, and expression in mammalian cells

Potassium is an essential nutrient which plays an important role in many aspects of plant growth and development. Plants have developed a number of highly specific mechanisms to take up potassium from the soil; these include the expression of K(+) transporters and potassium channels in root cells. Despite the fact that root epidermal and hair cells are in direct contact with the soil, the role of these tissues in K(+) uptake is not well understood. Here we report the molecular cloning and functional characterization of a novel potassium channel KDC1 which forms part of a new subfamily of plant K(in) channels. Kdc1 was isolated from carrot root RNA and in situ hybridization experiments show Kdc1 to be highly expressed in root hair cells. Expressing the KDC1 protein in Chinese hamster ovary cells identified it as a voltage and pH-dependent inwardly rectifying potassium channel. An electrophysiological analysis of carrot root hair protoplasts confirmed the biophysical properties of the Kdc1 gene product (KDC1) in the heterologous expression system. KDC1 thus represents a major K(+) uptake channel in carrot root hair cells.     

Ion conductance pathways in potato tuber (Solanum tuberosum) inner mitochondrial membrane

Single-ion channel activities were measured after reconstitution of potato tuber mitochondrial inner membranes into planar lipid bilayers. In addition to the recently described large-conductance Ca(2+)-activated potassium channel activity (Koszela-Piotrowska et al., 2009), the following mitochondrial ion conductance pathways were recorded: (i) an ATP-regulated potassium channel (mitoK(ATP) channel) activity with a conductance of 164+/-8pS, (ii) a large-conductance Ca(2+)-insensitive iberiotoxin-sensitive potassium channel activity with a conductance of 312 pS+/-23, and (iii) a chloride 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)-inhibited channel activity with a conductance of 117 pS+/-4. In isolated non-phosphorylating potato tuber mitochondria, individual and combined potassium channel activities caused significant (up to 14mV) but not collapsing K(+)-influx-induced membrane potential depolarisation. Under phosphorylating conditions, the coupling parameters were unchanged in the presence of high K(+) level, indicating that plant K(+) channels function as energy-dissipating systems that are not able to divert energy from oxidative phosphorylation. A potato tuber K(+) channel that is ATP-, 5-hydroxydecanonic acid-, glybenclamide-inhibited and diazoxide-stimulated caused low cation flux, modestly decreasing membrane potential (up to a few mV) and increasing respiration in non-phosphorylating mitochondria. Immunological analysis with antibodies raised against the mammalian plasma membrane ATP-regulated K(+) channel identified a pore-forming subunit of the Kir-like family in potato tuber mitochondrial inner membrane. These results suggest that a mitoK(ATP) channel similar to that of mammalian mitochondria is present in potato tuber mitochondria.     

Outward-rectifying K+ channel activities regulate cell elongation and cell division of tobacco BY-2 cells

Potassium ions (K⁺) are required for plant growth and development, including cell division and cell elongation/expansion, which are mediated by the K⁺ transport system. In this study, we investigated the role of K⁺ in cell division using tobacco BY-2 protoplast cultures. Gene expression analysis revealed induction of the Shaker -like outward K⁺ channel gene, NTORK1 , under cell-division conditions, whereas the inward K⁺ channel genes NKT1 and NtKC1 were induced under both cell-elongation and cell-division conditions. Repression of NTORK1 gene expression by expression of its antisense construct repressed cell division but accelerated cell elongation even under conditions promoting cell division. A decrease in the K⁺ content of cells and cellular osmotic pressure in dividing cells suggested that an increase in cell osmotic pressure by K⁺ uptake is not required for cell division. In contrast, K⁺ depletion, which reduced cell-division activity, decreased cytoplasmic pH as monitored using a fluorescent pH indicator, SNARF-1. Application of K⁺ or the cytoplasmic alkalizing reagent (NH₄)₂SO₄ increased cytoplasmic pH and suppressed the reduction in cell-division activity. These results suggest that the K⁺ taken up into cells is used to regulate cytoplasmic pH during cell division.     

Characterization of slowly inactivating KV{alpha} current in rabbit pulmonary neuroepithelial bodies: effects of hypoxia and nicotine

Pulmonary neuroepithelial bodies (NEB) form innervated cell clusters that express voltage-activated currents and function as airway O(2) sensors. We investigated A-type K(+) currents in NEB cells using neonatal rabbit lung slice preparation. The whole cell K(+) current was slowly inactivating with activation threshold of approximately -30 mV. This current was blocked approximately 27% by blood-depressing substance I (BDS-I; 3 microM), a selective blocker of Kv3.4 subunit, and reduced approximately 20% by tetraethylammonium (TEA; 100 microM). The BDS-I-sensitive component had an average peak value of 189 +/- 14 pA and showed fast inactivation kinetics that could be fitted by one-component exponential function with a time constant of (tau1) 77 +/- 10 ms. This Kv slowly inactivating current was also blocked by heteropodatoxin-2 (HpTx-2; 0.2 microM), a blocker of Kv4 subunit. The HpTx-2-sensitive current had an average peak value of 234 +/- 23 pA with a time constant (tau) 82 +/- 11 ms. Hypoxia (Po(2) = 15-20 mmHg) inhibited the slowly inactivating K(+) current by approximately 47%, during voltage steps from -30 to +30 mV, and no further inhibition occurred when TEA was combined with hypoxia. Nicotine at concentrations of 50 and 100 microM suppressed the slowly inactivating K(+) current by approximately 24 and approximately 40%, respectively. This suppression was not reversed by mecamylamine suggesting a direct effect of nicotine on these K(+) channels. In situ hybridization experiments detected expression of mRNAs for Kv3.4 and Kv4.3 subunits, while double-label immunofluorescence confirmed membrane localization of respective channel proteins in NEB cells. These studies suggest that the hypoxia-sensitive current in NEB cells is carried by slowly inactivating A-type K(+) channels, which underlie their oxygen-sensitive potassium currents, and that exposure to nicotine may directly affect their function, contributing to smoking-related lung disease.     

Cloning and electrophysiological analysis of KST1, an inward rectifying K+ channel expressed in potato guard cells.

Potassium uptake by guard cells represents part of the osmotic motor which drives stomatal opening. Patch-clamp measurements have identified inward rectifying K+ channels capable of mediating K+ uptake in guard cells and various other plant cell types. Here we report the molecular cloning and characterization of a voltage-dependent K+ channel (KST1) from potato (Solanum tuberosum L.) guard cells. In situ hybridization shows expression of kst1 in guard cells. Two-electrode voltage-clamp and patch-clamp studies of the gene product after cRNA injection into Xenopus oocytes identified KST1 as a slowly activating, voltage-dependent, inward rectifying K+ channel. The single channel current voltage curve was linear in the range -160 to +20 mV, with a deduced single channel conductance of 7 pS in symmetrical 100 mM K+. This channel type, modulated by pH changes within the physiological range, required ATP for activation. In line with the properties of a K(+)-selective channel, KST1 was permeable to K+, Rb+ and NH4+ and excluded Na+ and Li+. Cs+ at submillimolar concentrations blocked the channel in a voltage-dependent manner. Related studies on potato guard cell protoplasts confirmed the biophysical characteristics of the kst1 gene product (KST1) in the heterologous expression system. Therefore, KST1 represents a major K+ uptake channel in potato guard cells.     

Reduced functional expression of K(+) channels in vascular smooth muscle cells from rats made hypertensive with N{omega}-nitro-L-arginine

Smooth muscle membrane potential is determined, in part, by K(+) channels. In the companion paper to this article, we demonstrated that superior mesenteric arteries from rats made hypertensive with N(omega)-nitro-l-arginine (l-NNA) are depolarized and express less K(+) channel protein compared with those from normotensive rats. In the present study, we used patch-clamp techniques to test the hypothesis that l-NNA-induced hypertension reduces the functional expression of K(+) channels in smooth muscle. In whole cell experiments using a Ca(2+)-free pipette solution, current at 0 mV, largely due to voltage-dependent K(+) (K(V)) channels, was reduced approximately 60% by hypertension (2.7 +/- 0.4 vs. 1.1 +/- 0.2 pA/pF). Current at +100 mV with 300 nM free Ca(2+), largely due to large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels, was reduced approximately 40% by hypertension (181 +/- 24 vs. 101 +/- 28 pA/pF). Current blocked by 3 mM 4-aminopyridine, an inhibitor of many K(V) channel types, was reduced approximately 50% by hypertension (1.0 +/- 0.4 vs. 0.5 +/- 0.2 pA/pF). Current blocked by 1 mM tetraethylammonium, an inhibitor of BK(Ca) channels, was reduced approximately 40% by hypertension (86 +/- 14 vs. 53 +/- 19 pA/pF). Differences in BK(Ca) current magnitude are not attributable to changes in single-channel conductance or Ca(2+)/voltage sensitivity. The data support the hypothesis that l-NNA-induced hypertension reduces K(+) current in vascular smooth muscle. Reduced molecular and functional expression of K(+) channels may partly explain the depolarization and augmented contractile sensitivity of smooth muscle from l-NNA-treated rats.     

Potassium-chloride promiscuous channels in mitochondrial membranes

Mitochondrial membranes isolated from a rat heart muscle were incorporated into a bilayer lipid membrane (BLM) and channel currents were measured in 250/50 mmol/l KCl cis/trans solutions. The channel currents measured from -40 to +40 mV had various linear voltage-current relationships and K(+)/Cl(-) permeability ratios at distinct voltage ranges. The channels possessed K(+)-Cl(-) promiscuous property. Depending on voltage, membrane permeability suddenly switched from K(+) over Cl(-) to Cl(-) over K(+) and back. The channels had Cl(-)/K(+) > 1 permeability at potentials around 0 mV and the permeability was switched to K(+)/Cl(-) > 1 at more negative and positive potentials. The chloride channel blocker, 5-nitro-2-(phenylpropylamino)-benzoate (NPPB, 5 x 10(-5) mol/l), influenced properties of the promiscuous channels - it activated potassium conductance of the channels.     

大鼠胰腺β细胞离子通道的一些特性

实验以单个Ｗｉｓｔａｒ大鼠胰腺β细胞为对象,用穿孔膜片箝和细胞贴附式记录技术研究ＡＴＰ敏感Ｋ＾＋通道（ＫＡＴＰ）、延迟整流型Ｋ＾＋通道（ＫＤＲ）、Ｃａ＾２＋通道和Ｎａ＾＋通道的有关特性。结果表明：⑴ＫＡＴＰ通道的内流电导约６５ｐＳ,外流电导约３１ｐＳ,反转电位在－６０ｍＶ左右;⑵ＫＤＲ通道在延迟２０ｍｓ后达到最大激活,ＫＤＲ电流约为ＫＡＴＰ的１／３;⑶钙电流在０ｍＶ左右达到４０－６０ｐＡ的峰值,Ｌ     

Molecular identification and physiological roles of parotid acinar cell maxi-K channels

The physiological success of fluid-secreting tissues relies on a regulated interplay between Ca(2+)-activated Cl(-) and K(+) channels. Parotid acinar cells express two types of Ca(2+)-activated K(+) channels: intermediate conductance IK1 channels and maxi-K channels. The IK1 channel is encoded by the K(Ca)3.1 gene, and the K(Ca)1.1 gene is a likely candidate for the maxi-K channel. To confirm the genetic identity of the maxi-K channel and to probe its specific roles, we studied parotid glands in mice with the K(Ca)1.1 gene ablated. Parotid acinar cells from these animals lacked maxi-K channels, confirming their genetic identity. The stimulated parotid gland fluid secretion rate was normal, but the sodium and potassium content of the secreted fluid was altered. In addition, we found that the regulatory volume decrease in acinar cells was substantially impaired in K(Ca)1.1-null animals. We examined fluid secretion from animals with both K(+) channel genes deleted. The secretion rate was severely reduced, and the ion content of the secreted fluid was significantly changed. We measured the membrane potentials of acinar cells from wild-type mice and from animals with either or both K(+) channel genes ablated. They revealed that the observed functional effects on fluid secretion reflected alterations in cell membrane voltage. Our findings show that the maxi-K channels are critical for the regulatory volume decrease in these cells and that they play an important role in the sodium uptake and potassium secretion process in the ducts of these fluid-secreting salivary glands.     

Two novel cardiac atrial K+ channels, IK.AA and IK.PC

Two K(+)-selective channels in neonatal rat atrial cells activated by lipophilic compounds have been characterized in detail. The arachidonic acid-stimulated channel (IK.AA) had a slope conductance of 124 +/- 17 pS at +30 mV in symmetrical 140 mM potassium and a mean open time of approximately 1 ms, and was relatively voltage independent. IK.AA activity was reversibly increased by lowering pH to 6.0. Arachidonic acid was most effective in activating this channel, although a number of lipophilic compounds resulted in activation. Surprisingly, choline, a polar molecule, also activated the channel. A second K+ channel was activated by 10 microM phosphatidylcholine applied to the intracellular surface of inside-out atrial patches. This channel (IK.PC) had a slope conductance of 60 +/- 6 pS at +40 mV and a mean open time of approximately 0.6 ms, and was also relatively voltage independent. Fatty acids are probably monomeric in the membrane under the conditions of our recording; thus detergent effects are unlikely. Since a number of compounds including fatty acids and prostaglandins activated these two channels, an indirect, channel-specific mechanism may account for activation of these two cardiac K+ channels.     

Dominant negative guard cell K+ channel mutants reduce inward-rectifying K+ currents and light-induced stomatal opening in arabidopsis

Inward-rectifying potassium (K+(in)) channels in guard cells have been suggested to provide a pathway for K+ uptake into guard cells during stomatal opening. To test the proposed role of guard cell K+(in) channels in light-induced stomatal opening, transgenic Arabidopsis plants were generated that expressed dominant negative point mutations in the K+(in) channel subunit KAT1. Patch-clamp analyses with transgenic guard cells from independent lines showed that K+(in) current magnitudes were reduced by approximately 75% compared with vector-transformed controls at -180 mV, which resulted in reduction in light-induced stomatal opening by 38% to 45% compared with vector-transformed controls. Analyses of intracellular K+ content using both sodium hexanitrocobaltate (III) and elemental x-ray microanalyses showed that light-induced K+ uptake was also significantly reduced in guard cells of K+(in) channel depressor lines. These findings support the model that K+(in) channels contribute to K+ uptake during light-induced stomatal opening. Furthermore, transpirational water loss from leaves was reduced in the K+(in) channel depressor lines. Comparisons of guard cell K+(in) current magnitudes among four different transgenic lines with different K+(in) current magnitudes show the range of activities of K+(in) channels required for guard cell K+ uptake during light-induced stomatal opening.     

Vascular smooth muscle cell membrane depolarization after NOS inhibition hypertension

Nitric oxide (NO) synthase (NOS) inhibition with N(omega)-nitro-L-arginine (L-NNA) produces L-NNA hypertensive rats (LHR), which exhibit increased sensitivity to voltage-dependent Ca(2+) channel-mediated vasoconstriction. We hypothesized that enhanced contractile responsiveness after NOS inhibition is mediated by depolarization of membrane potential (E(m)) through attenuated K(+) channel conductance. E(m) measurements demonstrated that LHR vascular smooth muscle cells (VSMCs) are depolarized in open, nonpressurized (-44.5 +/- 1.0 mV in control vs. -36.8 +/- 0.8 mV in LHR) and pressurized mesenteric artery segments (-41.8 +/- 1.0 mV in control vs. -32.6 +/- 1.4 mV in LHR). Endothelium removal or exogenous L-NNA depolarized control VSMCs but not LHR VSMCs. Superfused L-arginine hyperpolarized VSMCs from both the control and LHR groups and reversed L-NNA-induced depolarization (-44.5 +/- 1.0 vs. -45.8 +/- 2.1 mV). A Ca(2+)-activated K(+) channel agonist, NS-1619 (10 microM), hyperpolarized both groups of arteries to a similar extent (from -50.8 +/- 1.0 to -62.5 +/- 1.2 mV in control and from -43.7 +/- 1.1 to -55.6 +/- 1.2 mV in LHR), although E(m) was still different in the presence of NS-1619. In addition, superfused iberiotoxin (50 nM) depolarized both groups similarly. Increasing the extracellular K(+) concentration from 1.2 to 45 mM depolarized E(m), as predicted by the Goldman-Hodgkin-Katz equation. These data support the hypothesis that loss of NO activation of K(+) channels contributes to VSMC depolarization in L-NNA-induced hypertension without a change in the number of functional large conductance Ca(2+)-activated K(+) channels.     

KV1.1 K(+) channels identification in human breast carcinoma cells: involvement in cell proliferation

Electrophysiological, immunocytochemical, and RT-PCR methods were used to identify a K(+) conductance not yet described in MCF-7 human breast cancer cells. A voltage-dependent and TEA-sensitive K(+) current was the most commonly observed in these cells. The noninactivating K(+) current (I(K)) was insensitive to iberiotoxin (100 nM) and charybdotoxin (100 nM) but reduced by alpha-dendrotoxin (alpha-DTX). Perfusion of alpha-DTX reduced a fraction of I(K) amplitude in a dose-dependent manner (IC(50) = 0.6 +/- 0.3 nM). This DTX sensitive I(K) exhibited a voltage threshold at -20 mV and was not inactivated. The time constant of activation was 5.3 +/- 2.2 ms measured at +60 mV. The averaged half-activation potential and slope factor values were 14 +/- 1.6 mV and 10 +/- 1.4, respectively. Immunocytochemical analysis demonstrated that plasma membrane was labeled by anti-Kv1.1 but not by anti-Kv1.2 nor anti-Kv1.3 antibodies. Furthermore, only Kv1.1 mRNA was detected in MCF-7 cells. Incubation in 1 and 10 nM alpha-DTX reduced cell proliferation by 20 and 30%, respectively. These data provide the first evidence of Kv1.1 K(+) channels expression in MCF-7 cells and indicate that these channels are implicated in cell proliferation.     

Potassium channels in plant cells

Potassium (K(+) ) is the most abundant inorganic cation in plant cells. Unlike animals, plants lack sodium/potassium exchangers. Instead, plant cells have developed unique transport systems for K(+) accumulation and release. An essential role in potassium uptake and efflux is played by potassium channels. Since the first molecular characterization of K(+) channels from Arabidopsis thaliana in 1992, a large number of studies on plant potassium channels have been conducted. Potassium channels are considered to be one of the best characterized class of membrane proteins in plants. Nevertheless, knowledge on plant potassium channels is still incomplete. This minireview focuses on recent developments in the research of potassium transport in plants with a strong focus on voltage-gated potassium channels.     

Evidence against functional interaction between aquaporin-4 water channels and Kir4.1 potassium channels in retinal Müller cells

Indirect evidence suggests that the Müller/glial cell water channel aquaporin-4 (AQP4) modulates K(+) channel function of the closely associated Kir4.1 protein. We used patch clamp to compare Kir4.1 K(+) channel function in freshly isolated Müller cells from retinas of wild-type (+/+) and AQP4 knock-out (-/-) mice. Immunocytochemistry showed a comparable Kir4.1 protein expression pattern in Müller cells from +/+ and -/- retinas, with greatest expression at their end feet. Osmotic water permeability was >4-fold reduced in -/- than in +/+ Müller cells. Resting membrane potential did not differ significantly in +/+ versus -/- Müller cells (-64 +/- 1 versus -64 +/- 1 mV, S.E., n = 24). Whole-cell K(+) currents recorded with a micropipette inserted into the cell soma were Ba(2+)-sensitive and showed no significant differences in magnitude in +/+ versus -/- Müller cells (1.3 +/- 0.1 versus 1.2 +/- 0.1 nA at -160 mV) or in inwardly rectifying current-voltage relationships. Spatially resolved K(+) currents generated by pulsed K(+) injections along Müller cell bodies were also comparable in +/+ versus -/- Müller cells. Single-channel cell-attached patch clamp showed comparable unitary conductance, current-voltage data, and open probability in +/+ versus -/- Müller cells. Thus, contrary to the generally accepted view, our results provide direct evidence against functionally significant AQP4 modulation of Müller cell Kir4.1 K(+) channel function.     

H2O2 activates redox- and 4-aminopyridine-sensitive Kv channels in coronary vascular smooth muscle

Previously, we demonstrated that coronary vasodilation in response to hydrogen peroxide (H(2)O(2)) is attenuated by 4-aminopyridine (4-AP), an inhibitor of voltage-gated K(+) (K(V)) channels. Using whole cell patch-clamp techniques, we tested the hypothesis that H(2)O(2) increases K(+) current in coronary artery smooth muscle cells. H(2)O(2) increased K(+) current in a concentration-dependent manner (increases of 14 +/- 3 and 43 +/- 4% at 0 mV with 1 and 10 mM H(2)O(2), respectively). H(2)O(2) increased a conductance that was half-activated at -18 +/- 1 mV and half-inactivated at -36 +/- 2 mV. H(2)O(2) increased current amplitude; however, the voltages of half activation and inactivation were not altered. Dithiothreitol, a thiol reductant, reversed the effect of H(2)O(2) on K(+) current and significantly shifted the voltage of half-activation to -10 +/- 1 mV. N-ethylmaleimide, a thiol-alkylating agent, blocked the effect of H(2)O(2) to increase K(+) current. Neither tetraethylammonium (1 mM) nor iberiotoxin (100 nM), antagonists of Ca(2+)-activated K(+) channels, blocked the effect of H(2)O(2) to increase K(+) current. In contrast, 3 mM 4-AP completely blocked the effect of H(2)O(2) to increase K(+) current. These findings lead us to conclude that H(2)O(2) increases the activity of 4-AP-sensitive K(V) channels. Furthermore, our data support the idea that 4-AP-sensitive K(V) channels are redox sensitive and contribute to H(2)O(2)-induced coronary vasodilation.