Synthesis and in vitro-anticancer and antimicrobial evaluation of some novel quinoxalines derived from 3-phenylquinoxaline-2(1H)-thione

Two novel series derived from 3-phenylquinoxaline-2(1H)-thione 2 and 2-(hydrazinocarbonylmethylthio)-3-phenylquinoxaline 6 have been synthesized. Eight out of twenty six new compounds were selected at the National Cancer Institute for evaluation of their in vitro-anticancer activity. Among them, compounds 3b, 3c, 4b, and 4c displayed moderate to strong growth inhibition activity against most of the tested sub-panel tumor cell lines with GI(50) 10(-5) to 10(-6 )molar concentrations. Compound 4b exhibited a significant value of percent tumor growth inhibition against breast cancer at concentration < 10(-8) M. Compound 4c showed moderate selectivity towards leukemia cell lines with GI(50) of 1.8 to 3.8 microM (selectivity ratio = 5.7). Preliminary antimicrobial testing revealed that compounds 7a, 7b, 8a, 11a, and 11b were as active as ampicillin against B. subtilis (MIC = 12.5 microg/mL). Compounds 7b and 8a were also nearly as active as ampicillin against E. coli (MIC = 12.5 microg/mL). In addition, compounds 4a, 7b, 10b, and 11a were as active as ampicillin against P. aerugenosa (MIC = 50 microg/mL). However, compounds 7b, 8a, and 10b showed mild activity against C. albicans (MIC = 50 microg/mL). The values of minimum bactericidal concentrations indicated that compounds 4a and 7b were bactericidal against B. subtilis and P. aerugenosa, respectively, while compound 10b was bactericidal against both organisms. However, compound 11a was bactericidal against E. coli, P. aerugenosa, and S. aureus.     

Preparation and in‐vitro Evaluation of 4‐Benzylsulfanylpyridine‐2‐carbohydrazides as Potential Antituberculosis Agents

A set of 4‐benzylsulfanylpyridine‐2‐carbohydrazides was synthesized and evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, non‐tuberculous mycobacteria, and multidrug‐resistant M. tuberculosis. The activities expressed as the minimum inhibitory concentration (MIC) fall into a range of 2 to 125 μmol/L, most often 4 to 32 μmol/L. The results revealed that the substituents on the benzyl moiety do not influence the antimycobacterial efficacy. The substances exhibited similar activities against sensitive and resistant strains of M. tuberculosis. Furthermore, compounds show low antiproliferative effect and cytotoxicity.     

Synthesis and antimicrobial activity of [2-[2-(N,N-disubstituted thiocarbamoyl-sulfanyl)-acylamino] thiazol-4-yl]acetic acid ethyl esters

[2-[2-(N, N-Disubstituted thiocarbamoyl-sulfanyl)acylamino ]thiazol-4-yl]acetic acid ethyl esters (3a-x) were synthesized by the reaction of potassium salts of N, N-disubstituted dithiocarbamoic acids with [2-(2-chloroalkanoyl)amino-thiazol-4-yl]acetic acid ethyl esters. The structures of the synthesized compounds were confirmed by elemental analyses, UV, IR, (1)H-NMR, and EI mass spectral data. The antimicrobial activities of all the compounds were investigated by microbroth dilution technique using Mueller-Hinton broth and Mueller-Hinton agar. In this study, Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis ATCC 12228, Escherichia coli ATCC 8739, Klebsiella pneumoniae ATCC 4352, Pseudomonas aeruginosa AT CC 1539, Salmonella typhi, Shigella flexneri, Proteus mirabilis ATCC 14153 and Candida albicans ATCC10231 were used as test microorganisms. Among the tested compounds 3a, d, e, f, h, k, w activity against S. epidermidis ATCC 12228 (MIC: 156 mg/L, 78 mg/L, 62.5 mg/L, 78 mg/L, 62.5 mg/L, 312 mg/L, 250 mg/L, respectively), compound 3d had some activity against S. aureus ATCC 6538 (MIC: 156 mg/L) and C. albicans ATCC 10231(MIC: 156 mg/L). Compounds 3l, 3x also evaluated for antituberculosis activity against Mycobacterium tuberculosis H37Rv using the BACTEC 460 radiometric system and BACTEC 12B medium. The preliminary results indicated that all of the tested compounds were inactive against the test organism.     

CYP2C19基因型和CYP2C9对人肝微粒体中氟西汀N-去甲基代谢的影响(英文)

目的:本实验旨在研究CYP2C19基因型人肝微粒体中氟西汀N-去甲基代谢的酶促动力学特点并鉴定参与此代谢途径的细胞色素P-450酶。方法:测定基因型CYP2C19肝微粒体中去甲氟西汀形成的酶促动力学。鉴定氟西汀N-去甲基酶活性与细胞色素P-450 2C9,2C19,1A2和2D6酶活性的相关性,同时应用各种细胞色素P-450酶的选择性抑制剂和化学探针进行抑制实验,从而确定参与氟西汀N-去甲基代谢的细胞色素P-450酶。结果:去甲氟西汀生成的酶促动力学数据符合单酶模型,并具有Michaelis-Menten动力学特征。当底物浓度为氟西汀25μmol/L和100μmol/L时,去甲氟西汀(N-FLU)的生成率分别与甲磺丁脲3-羟化酶活性显著相关(r_1=0.821,P_1=0.001;r_2=0.668,P_2=0.013),当底物浓度为氟西汀100μmol/L时,N-FLU的生成率与S-美芬妥因4’-羟化酶活性显著相关(r=0.717,P=0.006)。PM肝微粒中磺胺苯吡唑和醋竹桃霉素对氟西汀N-去甲基代谢的抑制作用显著大于EM(73％vs 45％,P<0.01)。结论:在生理底物浓度下,CYP2C9是催化人肝微粒体中氟西汀N-去甲基代谢的主要CYP-450酶;而高底物浓度时,以CYP2C19的作用为主。     

Novel 2-pyrazoline derivatives as potential anticonvulsant agents

A series of new 2-pyrazoline derivatives has been synthesized by reacting 3-(substituted-phenyl)-1-pyridin-2-yl-propenones using two routes one using thiosemicarbazide and the other by hydrazine hydrate. The chemical structures were established by IR, Mass, ¹H-NMR, ¹³C-NMR spectroscopic data, and elemental analysis. The anticonvulsant activity of the synthesized compounds was evaluated by the “maximal electroshock seizure” (MES) test and pentylenetetrazole (PTZ) test using male albino mice. Compounds 2e, 5-(naphthalene-1-yl)-3-(pyridine-2-yl)-4,5-dihydro-1H-pyrazole-1-carbothioic acid amide, and 3c, N-ethyl-5-(naphthalene-1-yl)-3-(pyridine-2-yl)-4,5-dihydro-1H-pyrazole-1-carbothioamide showed appreciable activity in the MES as well as PTZ test at all the evaluated doses.     

Antileishmanial and antibacterial activity of a new pyrazole derivative designated 4-[2-(1-(ethylamino)-2-methyl- propyl)phenyl]-3-(4-methyphenyl)-1-phenylpyrazole

Here, we report for the first time the synthesis and the antileishmanial activity of a new pyrazole derivative, namely 4-[2-(1-(ethylamino)-2-methylpropyl)phenyl]-3-(4-methyphenyl)-1-phenylpyrazole). Micromolar concentrations of this compound were found to inhibit the in vitro multiplication of Leishmania tropica, Leishmania major, and Leishmania infantum, three species causing different forms of leishmaniasis. Furthermore, the 50% inhibitory concentration (IC50) values for the compound are only slightly higher than those of amphotericin B, one of the most active antileishmanial agents used as a satisfactory substitute in cases not responding to pentostam. The IC50 values after 48 h for L. tropica, L. major, and L. infantum promastigote growth were 0.48 microg/mL, 0.63 microg/mL and 0.40 microg/mL, respectively for the compound, while they were 0.23 microg/mL, 0.29 microg/mL and 0.24 microg/mL, respectively for amphotericin B. We also tested this compound for its antibacterial activity against several bacteria. The strongest antibacterial activity was observed against Entrococcus feacalis and Staphylococcus aureus with a minimal inhibitory concentration (MIC) of 60 microg/mL.     

Synthesis, in vitro-antimycobacterial activity and cytotoxicity of some alkyl alpha-(5-aryl-1, 3, 4-thiadiazole-2-ylthio)acetates

A new series of alkyl alpha-[5-(5-nitro-2-furyl)-1, 3, 4- thiadiazole-2-ylthio] and alpha-[5-(1-methyl-5-nitro-2-imidazolyl)-1, 3, 4-thiadiazole-2-ylthio]acetates (6a-e, 6f-j) were synthesized and evaluated against Mycobacterium tuberculosis as part of the TAACF (Tuberculosis Antimicrobial Acquisition and Coordinating Facility) TB screening program. Primary screening was conducted at the single concentration of 6.25 microg/mL against M. tuberculosis H(37)Rv in BACTEC 12B medium using a broth microdilution assay, the Microplate Alamar Blue Assay (MABA). The minimum inhibitory concentration (MIC) was determined for compounds demonstrating >90 % growth inhibition in the primary screening. Seven compounds were efficient antimycobacterial agents showing MIC values ranging from 0.78 to 6.25 microg/mL. Among nitrofuran derivatives, methyl (6a), ethyl (6b), and benzyl (6e) esters displayed a good antituberculosis activity (MIC=0.78-3.13 microg/mL) and the others were inactive. In the nitro imidazole series, methyl (6f), ethyl (6g), propyl (6h) and butyl (6i) esters showed significant activity against M. tuberculosis while benzyl (6j) ester was inactive. Also, active compounds were screened by serial dilution to assess toxicity to a VERO cell line. A varying degree of toxicity was observed in nitrofuran and nitroimidazole derivatives (IC(50) = 2.3 - >10 microg/mL).     

Design and synthesis of new 1,3-benzdiazinan-4-one derivatives as selective cyclooxygenase (COX-2) inhibitors

A new group of regioisomeric 2,3-diaryl-1,3-benzdiazinan-4-ones, possessing a methyl sulfonyl pharmacophore, were synthesized and their biological activities were tested for cyclooxygenase-2 (COX-2) inhibitory activity. In vitro COX-1/COX-2 inhibition studies identified 3-(p-fluorophenyl)-2-(4-methylsulfonylphenyl)-1,3-benzdiazinane-4-one (2b) as a potent and highly selective (IC(50) = 0.07 μM; selectivity index = 572.8) COX-2 inhibitor.     

Synthesis of novel substituted 7-(benzylideneamino)-4-methyl-2H-chromen-2-one derivatives as anti-inflammatory and analgesic agents

A series of novel Schiff' base-containing a 7-amino-4-methylcoumarin moiety have been synthesized III a-l, characterized by spectroscopic data and studied for their anti-inflammatory and analgesic activity. The results of the anti-inflammatory and analgesic activity evaluation of 7-(substituted benzylideneamino)-4-methyl-2H-chromen-2-one derivatives III a-l proved to be comparable or more potent with respect to the reference drugs. In particular, compounds 7-(4-chlorobenzylideneamino)-4-methyl-2H-chromen-2-one III f, 7-(2,4-dichlorobenzylideneamino)-4-methyl-2H-chromen-2-one III g and 7-(4-bromobenzylideneamino)-4-methyl-2H-chromen-2-one III h exhibited potent anti-inflammatory and analgesic activity.     

Adenosine deaminase inhibitors. Synthesis and biological activity of deaza analogues of erythro-9-(2-hydroxy-3-nonyl)adenine

Two new deaza analogues of erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA, 1), 7-deaza-EHNA (6) and 1,3-dideaza-EHNA (11), were synthesized and evaluated for adenosine deaminase (ADA) inhibitory activity and compared with EHNA, 1-deaza-EHNA (2), and 3-deaza-EHNA (3). Substitution of a methine group for a nitrogen atom in the 7-position of the purine moiety of EHNA produces a dramatic drop in the inhibitory activity (Ki = 4 X 10(-4) M) whereas compounds 2 and 3 are still good inhibitors (Ki = 1.2 X 10(-7) M and 6.3 X 10(-9) M respectively). EHNA and its deaza analogues so far synthesized were also tested in vitro for their antiviral and antitumor activity in a range of cellular systems. EHNA and 1-deaza-EHNA are equiactive as inhibitors of human respiratory syncytial virus (HRSV) replication (MIC = 6.25 micrograms/mL) while the other compounds are inactive. On the other hand, all the examined compounds displayed an antitumor activity comparable to that of the reference compound 1-beta-D-arabinofuranosyladenine (ara-A), 7-deaza-EHNA being the most active of all. The results obtained showed that there is no correlation between adenosine deaminase inhibition and antiviral or antitumor activity in this series of compounds. 3-Deaza-EHNA, the most active inhibitor of ADA among the EHNA deaza analogues, greatly potentiates the antitumor activity of ara-A in vitro. In vivo activity was observed only when the two compounds were used in combination.     

中国人肝微粒体细胞色素P450 2A6的体外代谢特征

目的:观察人肝微粒体CYP2A6动力学特征.方法:采用生化分析法,体外研究化学异物对CYP2A6酶活性的影响.测定香豆素7-羟化酶的动力学参数.同时分析CYP2A6与Ⅱ相酶UGT之间的相关性.结果:CYP2A6活性差异8.8倍,K_m和V_(max)分别为0.25-1.56μmol·L~(-1)、1.41-8.70μmol·min~(-1)·g~(-1).匹鲁卡品、二乙基二硫代氨基甲酸盐、利福平明显抑制CYP2A6活性,IC_(50)值分别为 5.31μmol·L~(-1)、156.35μmol·L~(-1)和38.81μmol·L~(-1).α-萘黄酮、磺胺苯吡唑、醋竹桃霉素、酮康唑、泼尼松龙和阿奇霉素对香豆素7-羟化反应几乎无影响.CYP2A6与UGT_2之间存在显著相关性(r=0.9453,P<0.05).结论:中国人细胞色素P4502A6酶活性及动力学参数存在个体差异,CYP2A6与UGT_2之间有显著相关.除匹鲁卡品有CYP2A6选择性抑制作用外,利福平和二乙基二硫代氨基甲酸盐也明显抑制CYP2A6活性.     

In vitro activities of transition metal derivatives of ketoconazole and clotrimazole against a wild type strain of Saccharomyces cerevisiae in absence or presence of human neutrophils

In vitro activities of a series of gold, copper and ruthenium clotrimazole (CTZ, CAS 23593-75-1) and ketoconazole (KTZ, CAS 65277-42-1) derivatives were investigated individually and in combination with human neutrophils (PMNs) against a wild type strain of Saccharomyces cerevisiae. For 11 out of 12 tested metal complexes, the minimal inhibitory concentrations (MICs) at which 100 % of yeast growth was inhibited ranged from 0.75 to 3.0 micromol/L. The complex RuCl3(CTZ)3 x 2CH3OH (1f) (MIC = 0.75 micromol/L) was, although modestly, the only one able to increase the fungistatic activity of the parental drug (MIC = 1 micromol/L). On the other hand, at a sub-MIC concentration (0.5 micromol/L), the complexes [Cu(KTZ)Cl2]2 x 2H2O (2c) and RuCl2(KTZ)2 (2e) displayed synergistic fungicidal effects with PMNs whereas phagocytic capacity was enhanced by complexes [Cu(KTZ)3Cl2] (2b) and RuCl2(KTZ)2 (2e). The findings suggest that the metal-based agents may give rise to drugs with improved antifungal properties.     

Synthesis and in vitro antimicrobial evaluation of 5-(1-methyl-5-nitro-2-imidazolyl)-4H-1,2,4-triazoles

The increasing clinical importance of drug-resistant pathogens has lent additional urgency to antimicrobial research. Various 5-(1-methyl-5-nitro-2-imidazolyl)-4H-1,2,4-triazoles (4a-6f) were synthesized and tested in vitro for their antibacterial and antifungal activities. Compounds 4a and 4b exhibited significant effects against Bacillus subtilis at MIC ranges of 0.5-1 microg/mL and moderate effects against Staphylococcus aureus.     

7-chloro-3-(substituted benzylidene/phenyl ethylidene amino)-2-phenylquinazolin-4(3H)-ones: synthesis, antimicrobial and antitubercular evaluation

In this study, a series of 7-chloro-3-(substituted benzylidene/phenyl ethylidene amino)-2-phenyl quinazolin-4(3H)-ones (1–10) were prepared and evaluated for antitubercular activity against Mycobacterium tuberculosis (MTB). The antitubercular screening results indicated that 7-chloro-3-(4-(dimethylamino)benzylidene amino)-2-phenylquinazolin-4(3H)-one (10) was the most potent one (MIC?=?0.78?×?10^?3?μM) and exhibited activity equivalent to the standard compound isoniazid (MIC?=?0.80?×?10^?3?μM). Further, the synthesized compounds were tested for their antibacterial activity against Gram positive and Gram negative bacteria. The comparison of antibacterial and antimycobacterial results indicated that different structural requirements are necessary for a compound to be effective against bacterial and mycobacterial targets.     

Facile radiosynthesis of fluorine-18 labeled beta-blockers. Synthesis, radiolabeling, and ex vivo biodistribution of [18F]-(2S and 2R)-1-(1-fluoropropan-2-ylamino)-3-(m-tolyloxy)propan-2-ol

An efficient and general method has been developed for fluorine-18 labeling of beta-blockers that possess the propanolamine moiety. A new synthetically versatile intermediate, 3-(1-(benzyloxy)propan-2-yl)-2-oxooxazolidin-5-yl)methyl 4-methylbenzenesulfonate (13), was prepared and can be conjugated to any phenoxy core. To demonstrate the synthetic methodology, fluorinated derivatives of toliprolol were prepared, namely, [(18)F]-(2S and 2R)-1-(1-fluoropropan-2-ylamino)-3-(m-tolyloxy)propan-2-ol ((2S and 2R)-[(18)F]1). The radiosyntheses were accomplished in <1 h, with 20-24% (uncorrected for decay, n = 7) radiochemical yields, >96% radiochemical and >99% enantiomeric purities, with specific activities of 0.9-1.1 Ci/micromol (EOS). Ex vivo biodistribution studies with the radiotracers demonstrated excessively rapid washout that may limit their use for cerebral PET imaging.     

Design and syntheses of methyl 2‐methyl‐2‐[2‐(4‐benzoyl‐5‐phenyl‐7‐halo‐2‐azabicyclo[4.1.0]hept‐3‐ene)]acetates: novel inhibitors of cyclooxygenase‐2 (COX‐2) with analgesic‐antiinflammatory activity

A group of methyl 2‐methyl‐2‐[2‐(4‐benzoyl‐5‐phenyl‐7‐halo‐2‐azabicyclo[4.1.0]hept‐3‐ene)]acetates ( 10–15 ), and the related acetamide derivative ( 16 ), that possess a variety of C‐7 substituents (Br, Cl, F, H), were designed for evaluation as analgesic‐antiinflammatory agents. The effect of the C‐7 substituent(s) and the nature of the acetic acid ester (R¹ = Ome) or acetamide (R¹ = NH₂) moiety on analgesic activity was determined using a 4% NaCl‐induced abdominal constriction assay. Compounds 10–16 inhibited writhing by 36–82%, relative to the reference drugs aspirin (58% inhibition) and celecoxib (62% inhibition). The nature of the C‐7 substituents was a determinant of analgesic activity in the 7,7‐dihalo group of compounds where the relative activity profile was 7‐Cl₂ > 7‐Br₂ > 7‐F₂ > 7‐Cl,7‐F, and for 7‐monohalo compounds where the potency order was 7‐Br > 7‐Cl. Elaboration of the 7,7‐dibromo methyl acetate ester ( 10 ) to the corresponding acetamide derivative ( 16 ) enhanced analgesic activity. The nature of the 7‐halo substituent(s) in the 7,7‐dihalo group of compounds was a determinant of antiinflammatory activity, determined using the carrageenan‐induced rat paw edema assay, where the relative potency order was 7‐Br₂ > 7‐Cl₂ > 7‐F₂ > 7‐Cl,7‐F. The most potent 7,7‐dibromo compound ( 10 ) inhibited inflammation by 62%, relative to the reference drug ibuprofen (44%), and 10 inhibited COX‐2 (IC₅₀ = 26.4 μM) and COX‐1 (IC₅₀ = 227 μM) for a COX‐2 selectivity index of 8.6. Docking 10 in the active site of human COX‐2 showed it binds in the center of the COX‐2 binding site with the C‐5 phenyl ring oriented toward the acetylation site (Ser⁵³⁰), and the phenyl group of the C‐4 benzoyl moiety oriented in the vicinity of the COX‐2 secondary binding pocket near Val⁵²³. Drug Dev. Res. 49:75–84, 2000. © 2000 Wiley‐Liss, Inc.     

原花青素对脂多糖诱导RAW2647细胞COX-2酶活性、mRNA及蛋白表达的影响

目的探讨原花青素对脂多糖(LPS)诱导小鼠巨噬细胞株RAW264.7细胞COX-2酶活性及蛋白表达的影响。方法放射免疫法检测COX-2酶活性，RT-PCR检测COX-2 mRNA表达，Western blotting检测COX-2蛋白表达。结果原花青素(0.8，4和20 mg·L^-1)不影响LPS诱导RAW264.7细胞COX-2酶活性，可下调LPS诱导RAW264.7细胞COX-2 mRNA表达；原花青素(4和20 mg·L^-1)下调LPS诱导RAW264.7细胞COX-2蛋白表达。结论原花青素不影响LPS诱导RAW2647细胞COX-2酶活性，但对LPS诱导RAW264.7细胞COX-2 mRNA及蛋白表达抑制作用明显。     

Antioxidative and antitumor activity of derivatives of 4-beta-amino-4'-demethylepipodophyllotoxin and their structure-activity relationship

The purpose of this study was to investigate antioxidative and antitumor activity of derivatives of 4-beta-amino-4'-demethylepipodophyllotoxin (DmePod) and to analyze their structure-activity relationship. Homogenates of liver, heart and kidney of rats were used to measure malondialdehyde (MDA) generation spontaneously formed or induced by a hydroxyl free radical generation system (Fe2+-ascorbic acid) using thiobarbituric acid (TBA) assay. H2O2-induced red blood cells (RBC) hemolysis was determined spectrophotometrically. Superoxide anion (O2-*) from zymosan-stimulated neutrophils of rats was evaluated by nitroblue tetrazolium (NBT) reduction assay. Microculture tetrazolium (MTT) assay was used to determine the antitumor effects on K562 and K562/DOX cells. The results showed that all the tested compounds strongly inhibited MDA formation from tissue homogenates in a concentration-dependent manner following the rank GP7OH > GP7 > VP16 and GP7H > DmePod > Pod. The potency of antihemolysis for DmePod, GP7, GP7OH, GP7H and VP16 was similar among them according to their IC50 values by 13.6, 8.6, 11.7, 10.3, and 9.47 micromol x L(-1), respectively, whereas the potency for Pod was the weakest (IC50 > 320 micromol x L(-1)). GP7, GP7OH and VP16 (160-320 [micromol x L(-1)) significantly inhibited O2-* formation following the potency rank VP16 > GP7 > GP7OH. However, 320 micromol x L(-1) of DmePod, Pod or GP7H had no effect on O2-* formation. Meanwhile, all the tested compounds strongly inhibited K562 and K562/DOX cell proliferation for 96 h in a concentration-dependent manner. The resistance magnitude of GP7, GP7OH, VP16, and DmePod was 2.05, 2.21, 14.29, and 3.26, respectively, while antitumor activity of Pod and GP7H on K562/DOX cells was the weakest in all compounds. Taken together, the introduction of nitroxyl radical moieties into DmePod greatly enhances antioxidative and antitumor activity, and reverses drug resistance. Both NO* and NOH groups are essential active moieties.     

BAY 41-2272, a potent activator of soluble guanylyl cyclase, stimulates calcium elevation and calcium-activated potassium current in pituitary GH cells

The effects of BAY 41-2272, a nitric oxide-independent activator of soluble guanylyl cyclase, on Ca2+ signalling and ion currents were investigated in pituitary GH3 cells. Intracellular Ca2+ concentrations ([Ca2+]i) in these cells were increased by BAY 41-2272. Removing extracellular Ca2+ abolished the BAY 41-2272-induced increase in [Ca2+]i. After [Ca2+]i was elevated by BAY 41-2272 (300 nmol/L), subsequent application of 1-benzyl-3-(5'-hydroxymethyl-2'-furyl) indazole (YC-1; 1 micromol/L) did not increase [Ca2+]i further. In whole-cell recordings, BAY 41-2272 reversibly stimulated Ca2+-activated K+ current (I(K(Ca))) with an EC50 of 225 +/- 8 nmol/L. At 3 micromol/L, BAY 41-2272 slightly and significantly decreased L-type Ca2+ current.In the cell-attached configuration, BAY 41-2272 (300 nmol/L) enhanced the activity of large-conductance Ca2+-activated K+ (BK(Ca)) channels. After BK(Ca) channel activity was stimulated by spermine NONOate (30 micromol/L) or YC-1 (10 micromol/L) in cell-attached patches, subsequent application of BAY 41-2272 (300 nmol/L) further increased the channel open probability. In the inside-out configuration, BAY 41-2272 applied to the intracellular surface of excised patches enhanced BK(Ca) channel activity. Unlike 1 micromol/L paxilline, 1H-[1,2,4]oxadiazolol-[4,3a] quinoxalin-1-one (ODQ; 10 micromol/L) or heme (10 micromol/L) had no effect on BAY 41-2272-stimulated channel activity. BAY 41-2272 caused no shift in the activation curve of BK(Ca) channels; however, it did increase the Ca2+ sensitivity of these channels. At 300 nmol/L, BAY 41-2272 reduced the firing rate of spontaneous action potentials stimulated by thyrotropin-releasing hormone (10 micromol/L). The BK(Ca) channel activity was also enhanced by 300 nmol/L BAY 41-2272 in neuroblastoma IMR-32 cells. Therefore, the BAY 41-2272-induced increase in [Ca2+]i is primarily explained by an increase in Ca2+ influx. The BAY 41-2272-mediated simulation of IK(Ca) may result from direct activation of BKCa channels and indirectly as a result of elevated [Ca2+]i.