Angiotensin (1-7) participating in renal fibrosis by inhibiting intermediate conductance Ca2+-activated K+ channels protein expression / 解剖学报

Objective: To investigate the relationship between the protective effect of angiotensin (Ang) (1-7) and the protein expression of intermediate conductance Ca2+-activated K+ channels (KCa3. 1) in renal fibrosis. Methods: Totally 60 male mice were randomly divided into 5 groups: control group (WT); Ang II group: mice received Ang II [1.4 mg/(kg.d)] by hypodermic injection; Ang II blocker group (Losartan): mice received Ang II [1.4 mg/(kg.d)] and Losartan [40 mg/(kg.d)]by hypodermic injection; Ang (1-7) group; mice received Ang II [1.4 mg/(kg.d)] and Ang (1-7) [0. 14 mg/(kg.d)] by hypodermic injection; diminazene aceturate(DIZE) group: mice received Ang II [1.4 mg/(kg.d)] and DIZE [10 mg/(kg.d)] by hypodermic injection. After 4 weeks of continuous administration, the related indicators were detected. Masson staining was used to detect the collagen content, and Western blotting was used to detect the protein expression of collagen type I, collagen type DI and KCa3. 1 channel. Results: Collagen deposition in renal tissue increased significantly after 4 weeks of hypodermic injection of Ang II (n = 12,P<0.01) compared with the WT group, which suggested that the model of renal fibrosis was successfully reproduced. Ang II significantly increased the synthesis of collagen type I and DI (n=6,P<0.01) and increased the expression of Kca3. 1 channel protein (n=6,P< 0. 01) in renal tissues, while Ang (1-7) and ACE2 activator DIZE significantly inhibited those exchanges (n= 12 or 6,P< 0. 01). Conclusion: Ang (1-7) plays a protective role in the process of renal fibrosis, which may be related to the downregulation of KCa3. 1 channel protein expression in renal tissue.

Effect of extracellular potassium on the activity of distal renal tubule in mice / 上海交通大学学报（医学版）

Objective: To investigate the effect of extracellular potassium (K+) concentration on the activities of sodium chloride co-transporter (NCC) and large conductance Ca2+-activated K+ channel (BK) in distal renal tubule of mice. Methods: Six specific pathogen free (SPF) C57BL/6 mice aged 8 to 10 weeks were sacrificed,and the kidney slices were made with previously reported method. Then,these slices were incubated randomly in normal K+,high K+,BaCl2 and RbCl solutions,respectively. The abundance and phosphorylation level of NCC in kidney slices at different K+ concentrations and different time courses were detected by Western blotting. The overall and membrane expressions of BK in kidney slices were also detected after incubation with different K+ solutions for 2 h. Results: Compared with normal K+ solution,NCC phosphorylation level was significantly decreased after incubation with high K+ solution for 5,15,30 min (all P<0.05),and NCC phosphorylation level was also decreased after intervention with K+ channel inhibitor Ba2+ or Rb+ (both P<0.05). After the treatment with high K+ solution for 2 h,neither the overall cell expression of BKα subunit and β4 subunit,nor membrane expression of BKα subunit was found significant changes compared with normal K+ incubation. Conclusion: High K+ can directly down-regulate NCC phosphorylation level,which may be preparation for kaliuresis of the downstream tubule of distal convoluted tubule.

Construction of stable cell lines expressing large conductance Ca2+-activated K+ channel α-subunit and molecular mechanism of potassium excretion in this channel / 上海交通大学学报（医学版）

Objective: To construct stable cell lines expressing the large conductance Ca2+-activated K+ channel (MaxiK or BK) α-subunit and to explore the mechanism of potassium excretion via BKα channel. Methods:The BKα plasmid with Myc tag was constructed and transfected into HEK293 cell lines by lipofectamine 2000. The positive monoclonal cell lines were screened by G418, and the expression of BKα was detected by Western blotting and the location of BKα by immunofluorescence. The stable cell lines expressing BKα protein was cultured on slides to form a single cell layer, which was perfused with different potassium ion concentrations of 5 mmol/L and 100 mmol/L, and the single channel patch clamp recorded the ion flux of BKα. Wild type and mutants (G77R, G130R, C140R and R297C) of the inwardly rectifying potassium channel (Kir4.1) were transfected into HEK293 cells stably transfected with BKα, and then the membrane protein was extracted. The expression of BKα was detected by Western blotting. Results:Stable cell lines expressing BKα channel were selected from HEK293 cells after transfection and cellular immunofluorescence verified the expression of BKα channel and its expression on the cell membrane. The channel open frequency (Npo) of BKα increased rapidly when perfused with 100 mmol/L potassium. After being transfected with wild type or mutants of Kir4.1, the membrane expression of BKα in the stable cell lines showed significant difference among these groups (P<0.05). Conclusion:The HEK293 cell lines stably expressing BKα have been successfully constructed. BKα channel can be activated by high potassium solutions. The function of the BKα subunit can be related to Kir4.1 channel, which may be attributed to the depolarization of the cells transfected by Kir4.1 mutants.

Intermediate-conductance Ca2+-activated K+ channel: Research advances / 国际药学研究杂志

Intermediate-conductance Ca2+-activated K+ channel, also known as KCa3.1, IKCa and SK4, is widely distributed in fibroblasts, proliferating smooth muscle cells, endothelial cells, T lymphocytes, plasma cells, macrophages, and epithelial cells, and involved in the pathological and physiological processes such as vascular contraction, inflammation, calcification, tissue fibrosis, immune response, malignant tumor, internal and external secretory glands. In recent years, it has been found that blocking the KCa3.1 pathway or knockouting the gene can significantly prevent the pathophysiological process of its involvement. The recent use of the specific blocker TRAM-34 in animals and humans shows its safety and tolerability, providing a new direction for the treatment of related diseases. In this article, the research progress in KCa3.1 related diseases in recent years is reviewed.

Intermediate-conductance Ca2+-activated K+channel:research advances / 国际药学研究杂志

Intermediate-conductance Ca2+-activated K+channel ,also known as KCa3.1,IKCa and SK4,is widely distributed in fibroblasts,proliferating smooth muscle cells,endothelial cells,T lymphocytes,plasma cells,macrophages,and epithelial cells, and involved in the pathological and physiological processes such as vascular contraction,inflammation ,calcification,tissue fibrosis, immune response,malignant tumor,internal and external secretory glands. In recent years,it has been found that blocking the KCa3.1 pathway or knockouting the gene can significantly prevent the pathophysiological process of its involvement. The recent use of the specific blocker TRAM-34 in animals and humans shows its safety and tolerability,providing a new direction for the treatment of related diseases. In this article,the research progress in KCa3.1 related diseases in recent years is reviewed.

Activation of K+ channel by 1-EBIO rescues the head and neck squamous cell carcinoma cells from Ca2+ ionophore-induced cell death

Ion channels in carcinoma and their roles in cell proliferation are drawing attention. Intracellular Ca2+ ([Ca2+]i)-dependent signaling affects the fate of cancer cells. Here we investigate the role of Ca(2+)-activated K+ channel (SK4) in head and neck squamous cell carcinoma cells (HNSCCs) of different cell lines; SNU-1076, OSC-19 and HN5. Treatment with 1 microM ionomycin induced cell death in all the three cell lines. Whole-cell patch clamp study suggested common expressions of Ca(2+)-activated Cl- channels (Ano-1) and Ca(2+)-activated nonselective cation channels (CAN). 1-EBIO, an activator of SK4, induced outward K+ current (ISK4) in SNU-1076 and OSC-19. In HN5, ISK4 was not observed or negligible. The 1-EBIO-induced current was abolished by TRAM-34, a selective SK4 blocker. Interestingly, the ionomycin-induced cell death was effectively prevented by 1-EBIO in SNU-1076 and OSC-19, and the rescue effect was annihilated by combined TRAM-34. Consistent with the lower level of ISK4, the rescue by 1-EBIO was least effective in HN5. The results newly demonstrate the role of SK4 in the fate of HNSCCs under the Ca2+ overloaded condition. Pharmacological modulation of SK4 might provide an intriguing novel tool for the anti-cancer strategy in HNSCC.

Contradictory Effects of Superoxide and Hydrogen Peroxide on KCa3.1 in Human Endothelial Cells

Reactive oxygen species (ROS) are generated in various cells, including vascular smooth muscle and endothelial cells, and regulate ion channel functions. KCa3.1 plays an important role in endothelial functions. However, the effects of superoxide and hydrogen peroxide radicals on the expression of this ion channel in the endothelium remain unclear. In this study, we examined the effects of ROS donors on KCa3.1 expression and the K+ current in primary cultured human umbilical vein endothelial cells (HUVECs). The hydrogen peroxide donor, tert-butyl hydroperoxide (TBHP), upregulated KCa3.1 expression, while the superoxide donors, xanthine/xanthine oxidase mixture (X/XO) and lysopho-sphatidylcholine (LPC), downregulated its expression, in a concentration-dependent manner. These ROS donor effects were prevented by antioxidants or superoxide dismustase. Phosphorylated extracellular signal-regulated kinase (pERK) was upregulated by TBHP and downregulated by X/XO. In addition, repressor element-1-silencing transcription factor (REST) was downregulated by TBHP, and upregulated by X/XO. Furthermore, KCa3.1 current, which was activated by clamping cells with 1 microM Ca2+ and applying the KCa3.1 activator 1-ethyl-2-benzimidazolinone, was further augmented by TBHP, and inhibited by X/XO. These effects were prevented by antioxidants. The results suggest that hydrogen peroxide increases KCa3.1 expression by upregulating pERK and downregulating REST, and augments the K+ current. On the other hand, superoxide reduces KCa3.1 expression by downregulating pERK and upregulating REST, and inhibits the K+ current. ROS thereby play a key role in both physiological and pathological processes in endothelial cells by regulating KCa3.1 and endothelial function.

Mechanism of vasodilation by propofol in the rabbit renal artery

BACKGROUND: Propofol directly inhibits vascular reactivity. However, available information regarding the underlying mechanisms of propofol is poor. Therefore, mechanisms of the underlying relaxant action of propofol were investigated using rabbit renal arteries. METHODS: Propofol-induced relaxation of rabbit renal arteries was studied in contracted preparations with 50 mM KCl or 10microM histamine. Vessel tension was recorded with a pen recorder. We were interested in determining whether propofol-induced vasodilation is affected by endothelium-denudation, L-NG-nitroarginine methyl ester (L-NAME), tetraethylammonium (TEA), iberiotoxin, glibenclamide, 4-aminopyridine, 7-ethoxyresorufin, caffeic acid, baiclalein, ryanodine, and thapsigargin. RESULTS: Propofol-induced concentration-dependent vasodilation was not affected either by endothelium denudation or by L-NAME during histamine-induced contraction. The relaxing effect of propofol on histamine-induced contraction was inhibited by either TEA, a K+ channel inhibitor, or iberiotoxin (100 nM), a selective blocker of the large conductance Ca(2+)-activated K+ channel (BKCa channel). In contrast, the relaxing effect of propofol was unaffected by 10microM glibenclamide, an ATP-sensitive K+ channel blocker, by 5 mM 4-aminopyridine, a blocker of delayed rectifier, by 7-ethoxyresorufin, a cytochrome P450 inhibitor, by 10microM caffeic acid and 10microM baiclalein, lipooxygenase inhibitors, or by 10microM ryanodine and thapsigargin, Ca2+store inhibitors. CONCLUSIONS: These results suggest that the relaxant effect of propofol may result from activation of BKCa channels by inhibiting voltage-gated Ca2+ influx in a prolonged manner.

Oxidized Low-density Lipoprotein- and Lysophosphatidylcholine-induced Ca2+ Mobilization in Human Endothelial Cells

The effects of oxidized low-density lipoprotein (OxLDL) and its major lipid constituent lysophosphatidylcholine (LPC) on Ca2+ entry were investigated in cultured human umbilical endothelial cells (HUVECs) using fura-2 fluorescence and patch-clamp methods. OxLDL or LPC increased intracellular Ca2+ concentration ([Ca2+]i), and the increase of [Ca2+]i by OxLDL or by LPC was inhibited by La3+ or heparin. LPC failed to increase [Ca2+]i in the presence of an antioxidant tempol. In addition, store-operated Ca2+ entry (SOC), which was evoked by intracellular Ca2+ store depletion in Ca2+-free solution using the sarcoplasmic reticulum Ca2+ pump blocker, 2, 5-di-t-butyl-1, 4-benzohydroquinone (BHQ), was further enhanced by OxLDL or by LPC. Increased SOC by OxLDL or by LPC was inhibited by U73122. In voltage-clamped cells, OxLDL or LPC increased [Ca2+]i and simultaneously activated non-selective cation (NSC) currents. LPC-induced NSC currents were inhibited by 2-APB, La3+ or U73122, and NSC currents were not activated by LPC in the presence of tempol. Furthermore, in voltage-clamped HUVECs, OxLDL enhanced SOC and evoked outward currents simultaneously. Clamping intracellular Ca2+ to 1 micrometer activated large-conductance Ca2+-activated K+ (BKCa) current spontaneously, and this activated BKCa current was further enhanced by OxLDL or by LPC. From these results, we concluded that OxLDL or its main component LPC activates Ca2+-permeable Ca2+-activated NSC current and BKCa current simultaneously, thereby increasing SOC.

Mechanical Hyperalgesia Induced by Blocking Calcium-activated Potassium Channels on Capsaicin-sensitive Afferent Fiber

Small and large conductance Ca2+-activated K+ (SKCa and BKCa) channels are implicated in the modulation of neuronal excitability. We investigated how changes in peripheral KCa channel activity affect mechanical sensitivity as well as the afferent fiber type responsible for KCa channel-induced mechanical sensitivity. Blockade of SKCa and BKCa channels induced a sustained decrease of mechanical threshold which was significantly attenuated by topical application of capsaicin onto afferent fiber and intraplantar injection of 1-ethyl-2-benzimidazolinone. NS1619 selectively attenuated the decrease of mechanical threshold induced by charybdotoxin, but not by apamin. Spontaneous flinching and paw thickness were not significantly different after KCa channel blockade. These results suggest that mechanical sensitivity can be modulated by KCa channels on capsaicin-sensitive afferent fibers.

Differential Functional Expression of Clotrimazole-sensitive Ca2+-activated K+ Current in Bal-17 and WEHI-231 Murine B Lymphocytes

The intermediate conductance Ca2+-activated K+ channels (SK4, IKCa1) are present in lymphocytes, and their membrane expression is upregulated by various immunological stimuli. In this study, the activity of SK4 was compared between Bal-17 and WEHI-231 cell lines which represent mature and immature stages of murine B lymphocytes, respectively. The whole-cell patch clamp with high-Ca2+ (0.8microM) KCl pipette solution revealed a voltage-independent K+ current that was blocked by clotrimazole (1 mM), an SK4 blocker. The expression of mRNAs for SK4 was confirmed in both Bal-17 and WEHI-231 cells. The density of clotrimazole-sensitive SK4 current was significantly larger in Bal-17 than WEHI-231 cells (-11.4+/-3.1 Vs. -5.7+/-1.15 pA/pF). Also, the chronic stimulation of B cell receptors (BCR) by BCR-ligation (anti-IgM Ab, 3microgram/ml, 8~12 h) significantly upregulated the amplitude of clotrimazole-sensitive current from -11.4+/-3.1 to -53.1+/-8.6 pA/pF in Bal-17 cells. In WEHI-231 cells, the effect of BCR-ligation was significantly small (-5.7+/-1.15 to -9.0+/-1.00 pA/pF). The differential expression and regulation by BCR-ligation might reflect functional changes in the maturation of B lymphocytes.

VOCC and BKCa mRNA expression in kidney tissues of IgA nephropathy patients / 上海第二医科大学学报

0.05). ConclusionThe expression of VOCC mRNA and BKCa mRNA in kidney tissues of IgA nephropathy patients are abnormal.There is positive correlation between the abnormal expression of VOCC mRNA and BKCa mRNA and total glomerular pathological lesions integrals.The expression of VOCC mRNA and BKCa mRNA in kidney tissues of IgA nephropathy may serve as the indictor for the disease progression.

BKCa and atherogenesis / 基础医学与临床

Atherosclerosis is a kind of complex progressive inflammation.Exposure to atherogenic risk factors,particularly OxLDL,induces the activity of BKCa in endothelial cell,monocyte/macrophage(M?),vascular smooth muscle cell,platelet and other cells to activate,which precipitates dysfunction of the cells and therefore contributes to the development of atherosclerosis.This article briefly reviews the reseach progress in BKCa participating in the development of atherosclerosis.

Effects of chlorzoxazone on HepG2 tumor cells / 中国药理学通报

Aim To investigate effects of chlorzoxazone on survival and apoptosis of HepG2 cells.Methods The necrosis of HepG2 cells was evaluated by measurement of LDH release.The effects of chlorzoxazone on survival of HepG2 cells were assayed by MTT dyereduction.The effects of chlorzoxazone on cell apoptosis was analyzed by TUNEL method.The ultrastructure of HepG2 cells was observed by transmission electron microscope.Results Chlorzoxazone at concentrations of 100～500 ?mol?L-1 inhibited survival ratios of HepG2 cells in a dose-dependent manner significantly.Typical apoptotic changes were observed in HepG2 cells under the fluorescence microscope and transmission electron microscope.Apoptosis of HepG2 cells was induced after treatment of chlorzoxazone at concentrations from 100 ?mol?L-1 to 500 ?mol?L-1 for 48h,which showed obvious concentration-effect relationship.The apoptotic ratios of HepG2 cells were also increased when chlorzoxazone(100,200,300 and 500 ?mol?L-1) was treated for 24,48 and 72 h,which showed obvious time-effect relationship.Conclusion Chlorzoxazone inhibited HepG2 cells survival and induced cell apoptosis.

Membrane stretch increases the activity of Ca(2+)-activated K+ channels in rabbit coronary vascular smooth muscles

It has been proposed that Ca(2+)-activated K+ channels play an essential role in maintaining vascular tone during stretch of blood vessel. However, the underlying mechanism of stretch-induced change of Ca(2+)-activated K+ channel activities are still unknown. The present experiment was designed to investigate the effect of membrane stretch on these channels whose activity was measured from rabbit coronary smooth muscle cells using a patch clamp technique. Ca(2+)-activated K+ channel were identified by their Ca2+ and voltage dependencies and its large conductances as in other preparations. Perfusion of cells with a hypotonic solution, which mimics stretching the cell membrane by making a cell swelling, produced an increase in channel activity in cell-attached patch mode. The similar increase was observed when negative pressure was applied into the patch pipette for stretching the cell membrane within a patch area. In inside-out patch, stretch still increased channel activity even under the conditions which exclude the possible involvement of secondary messengers, or of transmembrane Ca2+ influx via stretch-activated cation channels. Pretreatment of arachidonic acid or albumin showed no effect on stretch-induced channel activation, excluding the possibility of fatty acids mediated channel activation during membrane stretch. These results indicate that the stretch may directly increase the activity of Ca(2+)-activated K+ channels in our experimental condition.

Increased activity of large conductance Ca2+-activated K+ channels in negatively-charged lipid membranes

The effects of membrane surface charge originated from lipid head groups on ion channels were tested by analyzing the activity of single large conductance Ca2+-activated K+ (maxi K) channel from rat skeletal muscle. The conductances and open-state probability (Po) of single maxi K channels were compared in three types of planar lipid bilayers formed from a neutral phosphatidyledianolamine (PE) or two negatively-charged phospholipids, phosphatidylserine (PS) and phosphatidylinositol (PI). Under symmetrical KCl concentrations (3 apprx 1,000 mM), single channel conductances of maxi K channels in charged membranes were 1.1 apprx 1.7 times larger than those in PE membranes, and the differences were more pronounced at the lower ionic strength. The average slope conductances at 100 mM KCl were 251 +/- 9.9, 360 +/- 8.7 and 356 +/- 12.4 (mean +/- SEM) pS in PE, PS and PI membranes respectively. The potentials at which Po was 1/2, appeared to have shifted left by 40 mV along voltage axis in the membranes formed with PS or PI. Such shift was consistently seen at pCa 5, 4.5, 4 and 3.5. Estimation of the effect of surface charge from these data indicated that maxi K channels sensed the surface potentials at a distance of 8 apprx 9 ANG from the membrane surface. In addition, similar insulation distance (7 apprx 9 ANG) of channel mouth from the bilayer surface charge was predicted by a 3-barrier-2-site model of energy profile for the permeation of K+ ions. In conclusion, despite the differences in structure and fluidity of phospholipids in bilayers, the activities of maxi K channels in two charged membranes composed of PS or PI were strikingly similar and larger than those in bilayers of PE. These results suggest that the enhancement of conductance and Po of maxi channels is mostly due to negative charges in the phospholipid head groups.

Dual action of d-tubocurarine on large-conductance Ca2+-activated K+ channels from rat brain reconstituted into planar lipid bilayer

Using the planar lipid bilayer method, we investigated the effect of d-tubocurarine (dTC) on the extracellular side of large-conductance Ca2+-activated K+ channel from rat brain. When the initial open probability (Po) of the channel was relatively high, dTC decreased channel activity in a concentration dependent manner. In contrast, when the initial Po was lower, sub-micro molar dTC increased channel activity by destabilizing the closed states of the channel. Further addition of dTC up to micro molar range decreased channel activity. This dual effect of dTC implicates that there exist at least two different binding sites for dTC.

The role of intracellular Mg2+ in regulation of Ca2+-activated K+ channel in pulmonary arterial smooth muscle cells of the rabbit

Although the Ca2+-activated K+ (IK,Ca) channel is known to play an important role in the maintenance of resting membrane potential, the regulation of the channel in physiological condition is not completely understood in vascular myocytes. In this study, we investigated the role of cytoplasmic Mg2+ on the regulation of IK,Ca channel in pulmonary arterial myocytes of the rabbit using the inside-out patch clamp technique. Mg2+ increased open probability (Po), but decreased the magnitude of single channel current. Mg2+-induced block of unitary current showed strong voltage dependence but increase of Po by Mg2+ was not dependent on the membrane potential. The apparent effect of Mg2+ might, thus, depend on the proportion between opposite effects on the Po and on the conductance of IK,Ca channel. In low concentration of cytoplasmic Ca2+, Mg2+ increased IK,Ca by mainly enhancement of Po. However, at very high concentration of cytoplasmic Ca2+, such as pCa 5.5, Mg2+ decreased IK,Ca. through the inhibition of unitary current. Moreover, Mg2+ could activate the channel even in the absence of Ca2+. Mg2+ might, therefore, partly contribute to the opening of IK,Ca channel in resting membrane potential. This phenomenon might explain why IK,Ca contributes to the resting membrane potential where membrane potential and concentration of free Ca2+ are very low.

The effect of sodium nitroprusside on muscle tension in guinea-pig ileum

Nitric oxide (NO) has been known as a mediator of nonadrenergic, noncholinergic inhibitory neurotransmitter in intestinal smooth muscles. It has been suggested that NO donor such as sodium nitroprusside (SNP) produces relaxation of smooth muscle via activation of guanylate cyclase and elevation of cGMP levels. We have therefore investigated the effects of NO, using SNP, on muscle tension in the longitudinal smooth muscle of guinea-pig ileum. The possible role of cGMP was also investigated as well as the involvement of K+ channel on SNP-induced inhibitory effect. The results are summarized as follows; high KCl-or CCh-activated contractions were inhibited by SNP in a concentration-dependent manner. 8-Br-cGMP also showed a similar effect in that of SNP. TEA (1 mM) significantly reduced the SNP-induced inhibitory effect. SNP-induced effect was further reduced by the presence of 10 mM TEA. On the other hand, 4-AP (0.1 mM), glibenclamide (10 muM) and apamin (0.1 muM) showed little effects on SNP-induced relaxation. Zaprinast significantly potentiated the SNP-induced inhibitory effect in all ranges. ODQ also significantly decreased the SNP-induced inhibitory effect. Pretreatment with CPA (10 muM) slightly reduced the SNP-induced inhibitory effect. From the above results, both effect mediated by NO and cGMP might be responsible for the activation of Ca2+/-activated K+ channel by SNP in guinea-pig ileum. And this K+ channel activation by SNP also contributes to the SNP-induced membrane hyperpolarization and relaxation.

Activation of Ca(2+)-activated K+ channels by beta agonist in rabbit coronary smooth muscle cells

Isoproterenol (ISO), a beta agonist, causes hyperpolarization of coronary smooth muscle cells via an increase in K+ conductance. This hyperpolarization may cause the coronary vasorelaxation by decreasing the cytoplasmic Ca2+ concentration. It is well known that the activation of beta adrenoreceptors stimulates the adenylate cyclase activity, and the resulting K+ channel phosphorylation by cAMP-dependent protein kinase may be responsible for ISO-induced increase in K+ channel activity. However, it is not clear whether the increase in K+ channel activity by ISO is exclusively due to the activation of adenylate cyclase or not. In this research, the effect of ISO on the isometric tension and the mechanism of ISO-induced K+ channel activation were investigated in various patch clamp conditions. The summarized results are as follows. ISO- and pinacidil induced vasorelaxation was significantly inhibited by the application of TEA or by increasing the external K+ concentration. In the whole cell clamp mode, application of ISO increased K+ outward current, and this effect was completely eliminated by propranolol. In the cell-attached patch, application of ISO or forskolin increased Ca(2+)-activated K+ channel activity. Application of ISO to the bath in the outside-out patches or GTP in the inside-out patches stimulated Ca(2+)-activated K+ channels. From the above results, both A-kinase dependent channel phosphorylation and direct GTP-binding protein mediated effect might be responsible for the the activation of Ca(2+)-activated K+ channel by ISO in rabbit coronary smooth muscle cells. And this K+ channel activation also contributes to the ISO-induced vasorelaxation.