Design and synthesis of novel anti-multidrug-resistant staphylococcus aureus derivatives of glycyrrhetinic acid by blocking arginine biosynthesis, metabolic and H2S biogenesis.

With the soaring number of multidrug-resistant bacteria, it is imperative to develop novel efficient antibacterial agents and discovery new antibacterial pathways. Herein, we designed and synthesized a series of structurally novel glycyrrhetinic acid (GA) derivatives against multidrug-resistant Staphylococcus aureus (MRSA). The in vitro antibacterial activity of these compounds was evaluated using the microbroth dilution method, agar plate coating experiments and real-time growth curves, respectively. Most of the target derivatives showed moderate antibacterial activity against Staphylococcus aureus (S. aureus) and MRSA (MIC = 3.125-25 µM), but inactivity against Escherichia coli (E. Coli) and Pseudomonas aeruginosa (P. aeruginosa) (MIC > 200 µM). Among them, compound 11 had the strongest antibacterial activity against MRSA, with an MIC value of 3.125 µM, which was 32 times and 64 times than the first-line antibiotics penicillin and norfloxacin, respectively. Additionally, transcriptomic (RNA-seq) and quantitative polymerase chain reaction (qPCR) analysis revealed that the antibacterial mechanism of compound 11 was through blocking the arginine biosynthesis and metabolic and the H2S biogenesis. Importantly, compound 11 was confirmed to have good biocompatibility through the in vitro hemolysis tests, cytotoxicity assays and the in vivo quail chicken chorioallantoic membrane (qCAM) experiments. Current study provided new potential antibacterial candidates from glycyrrhetinic acid derivatives for clinical treatment of MRSA infections.

Synthesis and biological activity evaluation of podophyllotoxin-linked bile acid derivatives as potential anti-liver cancer agents.

Podophyllotoxin's undifferentiated cytotoxicity and poor selectivity limit its clinical application. To improve above disadvantages, conjugation of bile acids with podophyllotoxin could improve cell line selectivity of liver cancer to achieve clinical translation further. Enlightened by the bile acids' moiety magic characters, thirty podophyllotoxin-linked bile acid derivatives had been designed and synthesized. The cytotoxicity of these compounds in vitro was evaluated on HepG2, HCT-116, A549 and MDCK cell lines. After conjunction with bile acids, most of the derivatives (IC50 = 0.066-0.831 µM) were more potent against above three types of tumor cells than Etoposide (VP-16, IC50 = 4.319-41.080 µM) and exhibited similar antitumor activity compared with doxorubicin (DOX, IC50 = 0.230-0.745 µM). Moreover, structure-activity relationship displayed the length of the linker chain between podophyllotoxin and bile acids affected the cytotoxicity. Especially, compound 23 exhibited strong activity against HepG2 cell lines (IC50 = 0.188 ± 0.01 µM) than MDCK cell lines (IC50 = 4.780 ± 0.50 µM) and its SI (IC50MDCK/IC50HepG2) value of compound 23 was 25.4. Further antitumor mechanism studies showed that compound 23 acted as Topo Ⅱ inhibition and induced cell apoptosis with S cell cycle arrest. In particular, compound 23 showed valid antitumor efficacy at 10 mg/kg by intraperitoneal administration with a tumor inhibition rate of 60.9% in the Hepa1-6 xenograft mice model. The current research displayed that introduction of bile acids contributed to improve selectivity and activity to cell, and compound 23 could be a promising anti-tumor candidate.

Design, Synthesis, and Cytotoxic Analysis of Novel Hederagenin⁻Pyrazine Derivatives Based on Partial Least Squares Discriminant Analysis.

Hederagenin (He) is a novel triterpene template for the development of new antitumor compounds. In this study, 26 new He⁻pyrazine derivatives were synthetized in an attempt to develop potent antitumor agents; they were screened for in vitro cytotoxicity against tumor and non-tumor cell lines. The majority of these derivatives showed much stronger cytotoxic activity than He. Remarkably, the most potent was compound 9 (half maximal inhibitory concentration (IC50) was 3.45 ± 0.59 µM), which exhibited similar antitumor activities against A549 (human non-small-cell lung cancer) as the positive drug cisplatin (DDP; IC50 was 3.85 ± 0.63 µM), while it showed lower cytotoxicity on H9c2 (murine heart myoblast; IC50 was 16.69 ± 0.12 µM) cell lines. Compound 9 could induce the early apoptosis and evoke cell-cycle arrest at the synthesis (S) phase of A549 cells. Impressively, we innovatively introduced the method of cluster analysis modeled as partial least squares discriminant analysis (PLS-DA) into the structure⁻activity relationship (SAR) evaluation, and SAR confirmed that pyrazine had a profound effect on the antitumor activity of He. The present studies highlight the importance of pyrazine derivatives of He in the discovery and development of novel antitumor agents.

PSMA-Oriented Target Delivery of Novel Anticancer Prodrugs: Design, Synthesis, and Biological Evaluations of Oligopeptide-Camptothecin Conjugates.

Clinical applications of camptothecin (CPT) have been heavily hindered due to its non-targeted toxicity, active lactone ring instability, and poor water solubility. Targeted drug delivery systems may offer the possibility to overcome the above issues as reported. In this research, a series of prostate-specific membrane antigen (PSMA)-activated CPT prodrugs were designed and synthesized by coupling water-soluble pentapeptide, a PSMA hydrolyzing substrate, to CPT through an appropriate linker. The cytotoxicity of CPT prodrugs was masked temporarily until they were hydrolyzed by the PSMA present within the tumor sites, which restored cytotoxicity. The in vitro selective cytotoxic activities of the prodrugs were evaluated against PSMA-expressing human prostate cancer cells LNCaP-FGC and non-PSMA-expressing cancer cells HepG2, Hela, MCF-7, DU145, PC-3 and normal cells MDCK, LO2 by standard methylthiazol tetrazolium (MTT) assay. Most of the newly synthesized CPT prodrugs showed excellent selective toxicity to PSMA-producing prostate cancer cells LNCaP-FGC with improved water solubility. From among the library, CPT-HT-J-ZL12 showed the best cytotoxic selectivity between the PSMA-expressing and the non-PSMA-expressing cancer cells. For example, the cytotoxicity of CPT-HT-J-ZL12 (IC50 = 1.00 ± 0.20 µM) against LNCaP-FGC (PSMA⁺) was 40-fold, 40-fold, 21-fold, 5-fold and 40-fold, respectively, higher than that against the non-PSMA-expressing cells HepG2 (IC50 > 40.00 µM), Hela (IC50 > 40.00 µM), MCF-7 (IC50 = 21.68 ± 4.96 µM), DU145 (IC50 = 5.40 ± 1.22 µM), PC-3 (IC50 = 42.96 ± 3.69 µM) cells. Moreover, CPT-HT-J-ZL12 exhibited low cytotoxicity (IC50 > 40 µM) towards MDCK and LO2 cells. The cellular uptake experiment demonstrated the superior PSMA-targeting ability of the CPT-HT-J-ZL12, which was significantly accumulated in LNCaP-FGC (PSMA⁺), while it was minimized in HepG2 (PSMA-) cells. Further cell apoptosis analyses indicated that it showed a dramatically higher apoptosis-inducing activity in LNCaP-FGC (PSMA⁺) cells than in HepG2 (PSMA-) cells. Cell cycle analysis indicated that CPT-HT-J-ZL12 could induce cell cycle arrest at the S phase.

Enriched environment during adolescence modulates lipid metabolism and emotion-related behaviors in mice.

Enriched environment (EE) is an important animal experimental paradigm to decipher gene-environment interaction. It is thought to be efficient in aiding recovery from certain metabolism disorders or cognitive impairments. Recently, the effects of EE during adolescence in mice gradually draw much attention. We first established an EE model in adolescent mice, dissected lipid metabolism, and further examined baseline level of anxiety and depression by multiple behavioral tests, including open field test (OFT), elevated zero maze (EZM), tail suspension test (TST), and forced swimming test (FST). EE mice exhibited lower weights, lower cholesterol than standard housing (SH) mice. Behaviorally, EE mice traveled more distance and had higher velocity than SH mice in OFT and EZM. Besides, EE mice showed reduced anxiety levels in OFT and EZM. Furthermore, EE mice also had less immobility time than SH mice in TST and FST. Thus, these results suggest that EE during adolescence has metabolic and behavioral benefits in mice.

Exosomes-transferred LINC00668 Contributes to Thrombosis by Promoting NETs Formation in Inflammatory Bowel Disease.

Epidemiological studies show an association between inflammatory bowel disease (IBD) and increased risk of thrombosis. However, how IBD influences thrombosis remains unknown. The current study shows that formation of neutrophil extracellular traps (NETs) significantly increased in the dextran sulfate sodium (DSS)-induced IBD mice, which in turn, contributes to thrombus formation in a NETs-dependent fashion. Furthermore, the exosomes isolated from the plasma of the IBD mice induce arterial and venous thrombosis in vivo. Importantly, proinflammatory factors-exposed intestinal epithelial cells (inflamed IECs) promote neutrophils to release NETs through their secreted exosomes. RNA sequencing revealed that LINC00668 is highly enriched in the inflamed IECs-derived exosomes. Mechanistically, LINC00668 facilitates the translocation of neutrophil elastase (NE) from the cytoplasmic granules to the nucleus via its interaction with NE in a sequence-specific manner, thereby inducing NETs release and thrombus formation. Importantly, berberine (BBR) suppresses the nuclear translocation of NE and subsequent NETs formation by inhibiting the interaction of LINC00668 with NE, thus exerting its antithrombotic effects. This study provides a novel pathobiological mechanism linking IBD and thrombosis by exosome-mediated NETs formation. Targeting LINC00668 can serve as a novel molecular treatment strategy to treat IBD-related thrombosis.

2-Aminoethoxydiphenyl borate blocks electrical coupling and inhibits voltage-gated K+ channels in guinea pig arteriole cells.

2-Aminoethoxydiphenyl borate (2-APB) analogs are potentially better vascular gap junction blockers than others widely used, but they remain to be characterized. Using whole cell and intracellular recording techniques, we studied the actions of 2-APB and its potent analog diphenylborinic anhydride (DPBA) on vascular smooth muscle cells (VSMCs) and endothelial cells in situ of or dissociated from arteriolar segments of the cochlear spiral modiolar artery, brain artery, and mesenteric artery. We found that both 2-APB and DPBA reversibly suppressed the input conductance (G(input)) of in situ VSMCs (IC(50) ≈ 4-8 µM). Complete electrical isolation of the recorded VSMC was achieved at 100 µM. A similar gap junction blockade was observed in endothelial cell tubules of the spiral modiolar artery. Similar to the action of 18ß-glycyrrhetinic acid (18ß-GA), 2-APB and DPBA depolarized VSMCs. In dissociated VSMCs, 2-APB and DPBA inhibited the delayed rectifier K(+) current (I(K)) with an IC(50) of ∼120 µM in the three vessels but with no significant effect on G(input) or the current-voltage relation between -140 and -40 mV. 2-APB inhibition of I(K) was more pronounced at potentials of ≤20 mV than at +40 mV and more marked on the fast component than on the slow component, which was mimicked by 4-aminopyridine but not by tetraethylammonium, nitrendipine, or charybdotoxin. In contrast, 18ß-GA caused a linear inhibition of I(K) between 0 to +40 mV, which was similar to the action of tetraethylammonium or charybdotoxin. Finally, the 2-APB-induced inhibition of electrical coupling and I(K) was not affected by the inositol 1,4,5-trisphosphate receptor antagonist xestospongin C. We conclude that 2-APB analogs are a class of potent and reversible vascular gap junction blockers with a weak side effect of voltage-gated K(+) channel inhibition. They could be gap junction blockers superior to 18ß-GA only when Ca(2+)-actived K(+) channel inhibition by the latter is a concern but inositol 1,4,5-trisphosphate receptor and voltage-gated K(+) channel inhibitions are not.

A novel drug delivery system of mixed micelles based on poly(ethylene glycol)-poly(lactide) and poly(ethylene glycol)-poly(ɛ-caprolactone) for gambogenic acid.

In this study, a novel mixed polymeric micelles formed from biocompatible polymers, poly(ethylene glycol)-poly(lactide) (mPEG-PLA) and poly(ethylene glycol)-poly(ɛ-caprolactone) (mPEG-PCL), used as a novel nanocarrier to encapsulate gambogenic acid (GNA). GNA-loaded mixed polymeric micelles (GNA-MMs) was prepared by cosolvent evaporation method. The mean average size of GNA-MMs was (83.23 ± 1.06) nm (n = 3) and entrapment efficiency (EE%) of GNA-MMs was (90.18 ± 2.59) % (n = 3) as well as (12.36 ± 0.64) % (n = 3) for drug loading (DL%). Transmission electron microscopy revealed that the GNA-MMs were spherical with "core-shell" structures. Compared with free GNA solution, in vitro release of GNA from GNA-MMs showed a two-phase sustained release profile: an initial relatively fast phase and followed by a slower release phase. Pharmacokinetic results also indicated that the GNA-MMs have longer systemic circulation time and slower plasma elimination rate than free GNA solution. Moreover, the in vitro cytotoxicity assay showed that the IC50 values on HepG2 cells for GNA-MMs and free GNA were (5.67 ± 0.02) µM and (9.02 ± 0.03) µM, respectively. In addition, GNA-MMs significantly increased the HepG2 cellular apoptosis in a concentration-dependent manner. In conclusion, the results showed that mPEG-PLA/mPEG-PCL mixed micelles may serve as an ideal drug delivery system for GNA to prolong drug circulation time in body, enhance bioavailability and retained its potent antitumor effect.

Design, synthesis and biological evaluation of cinnamic acid derivatives with synergetic neuroprotection and angiogenesis effect.

As for complex brain diseases involved with multiple pathogenic factors, it is extremely difficult to achieve curative effect by acting on a single target. Multi-approach drugs provide a promising prospect in the treatment of complex brain diseases and have been attracting more and more interest. Enlightened by synergetic effect of combination in traditional herb medicines, forty-two novel cinnamic acid derivatives were designed and synthesized by introducing capsaicin and/or ligustrazine moieties to enhance biological activities in both neurological function and neurovascular protection. Elevated levels of cell viability on human brain microvascular endothelium cell line (HBMEC-2) and human neuroblastoma cell line (SH-SY5Y) against free radical injury were observed in most of compounds. Among them, compound 14a exhibited the most potent activities with a significant EC50 value of 3.26 ±â€¯0.16 µM (HBMEC-2) and 2.41 ±â€¯0.10 µM (SH-SY5Y). Subsequently, the results of morphological staining and flow cytometry analysis experiments on both cell lines showed that 14a had the potential to block apoptosis, maintain cell morphological integrity and protect physiological function of mitochondria. Moreover, 14a displayed specific angiogenesis effect in the chick chorioallantoic membrane (CAM) assay; and the results of RT-PCR suggested that the mechanism for angiogenesis effect was associated with the enhancement of the expressions of VEGFR2 mRNA in chick embryo. Preliminary structure-activity relationship was analyzed. The above evidences suggested that conjunctures gained by combining active ingredients in traditional herb medicines deserved further study and might provide references in discovering dual-effective lead compounds for brain diseases.

Synthesis and biological activity of glycyrrhetinic acid derivatives as antitumor agents.

Glycyrrhetinic acid (GA) had been the star anticancer lead compound and appealed to many scientists all over the world; however, its antitumor activity was not potent enough. To improve GA's cytoxicity and explore the effect of bonding mode on antitumor activity, 32 compounds including GA-OH series (GO, esters in C-3 position) and GA-NH2 series (GN, with amide linkages in C-3 position) had been designed and synthesized. All the compounds were screened for in vitro cytotoxicity against A549, HepG2, MCF-7, Hela and MDCK cell lines. As a result, all the de-protected (without Boc group) derivatives showed much stronger cytotoxic activity than GA, and surprisingly enough, all the GN series of the compounds were more potent than GO series against various tumor cells. Among them, the compound 26 (amide linkages in C-3 position) exhibited stronger antitumor activity against A549 cell line (IC50 = 2.109 ±â€¯0.11 µM) than the positive drug cisplatin (IC50 = 9.001 ±â€¯0.37 µM). Further studies indicated that compound 26 could induce A549 apoptosis via nuclei fragmentation. The detection of apoptosis and cell cycle analysis indicated that compound 26 could induce the early apoptosis and prevent A549 cells transition from S to G2 phase. Furthermore, the structure-activity relationships were briefly discussed. Among which, current study displayed amide linkages in C-3 position could effectively enhance GA cytotoxicity, providing a new modification strategy for further study.

ACh-induced depolarization in inner ear artery is generated by activation of a TRP-like non-selective cation conductance and inactivation of a potassium conductance.

Adequate cochlear blood supply by the spiral modiolar artery (SMA) is critical for normal hearing. ACh may play a role in neuroregulation of the SMA but several key issues including its membrane action mechanisms remain poorly understood. Besides its well-known endothelium-dependent hyperpolarizing action, ACh can induce a depolarization in vascular cells. Using intracellular and whole-cell recording techniques on cells in guinea pig in vitro SMA, we studied the ionic mechanism underlying the ACh-depolarization and found that: (1) ACh induced a DAMP-sensitive depolarization when intermediate conductance KCa channels were blocked by charybdotoxin or nitrendipine. The ACh-depolarization was associated with a decrease in input resistance (R(input)) in high membrane potential (V(m)) ( approximately -40 mV) cells but with no change or an increase in R input in low Vm ( approximately -75 mV) cells. ACh-depolarization was attenuated by background membrane depolarization from approximately -70 mV in the majority of cells; (2) ACh-induced inward current in smooth muscle cells embedded in a SMA segment often showed a U-shaped I/V curve, the reversal potential of its two arms being near EK and 0 mV, respectively; (3) ACh-depolarization was reduced by low Na+, zero K+ or 20mM K+ bath solutions; (4) ACh-depolarization was inhibited by La3+ in all cells tested, by 4-AP and flufenamic acid in low Vm cells, but was not sensitive to Cd2+, Ni2+, nifedipine, niflumic acid, DIDS, IAA94, linopirdine or amiloride. We conclude that ACh-induced vascular depolarization was generated mainly by activation of a TRP-like non-selective cation channel and by inactivation of an inward rectifier K+ channel.

Synthesis and biological evaluation of podophyllotoxin derivatives as selective antitumor agents.

To improve podophyllotoxin's cytotoxicity and selective effect, twenty-two podophyllotoxin derivatives had been designed and synthesized. The cytotoxicity of these compounds was evaluated on A549, MCF-7, HepG2 and L-02 cell lines. As a result, most of the compounds were more potent than the positive drugs Etoposide (VP-16) and Doxorubicin which were widely used in clinical for antitumor. There were no magnitude differences about these de-protected (without Boc group) podophyllotoxin amino acid derivatives' cytotoxicity between three tumor cell lines and normal hepatic L-02 cells. Interestingly, some protected (with Boc group) amino acid derivatives and some ligustrazine derivatives showed high selectivity, especially the compound 2 (sarcosine derivative with Boc group). It exhibited highly selectivity both on the cancer cells and the normal cells. The IC50 of compound 2 was 9.5 ±â€¯0.03 nM, 132.6 ±â€¯24.1 nM, 96.4 ±â€¯1.3 nM and 160.2 ±â€¯4.7 nM against A549, MCF-7, HepG2 and L-02 cells, respectively. The SI (IC50L-02/IC50A549) value of compound 2, Doxorubicin and Etoposide was 16.9, 0.2 and 0.5, respectively. Meanwhile, SI (IC50MCF-7/IC50A549) value and SI (IC50HepG2/IC50A549) value of compound 2 were 14.0 and 10.1, respectively. In summary, compound 2 showed high selectivity especially on A549 cells. Further research on cell apoptosis indicated that compound 2 could induce apoptosis of A549 cells through nuclei fragmentation and had lower toxicity to normal hepatic L-02 cells. The detection of apoptosis and cell cycle analysis indicated that compound 2 induced A549 cells apoptosis and prevented A549 cells transition from S to G2 phase while there were no obvious changes on L-02 cells. Moreover, the structure-activity relationships of these derivatives were briefly discussed.

[Analysis of Factors Influencing Peripheral Blood Stem Cell Collection of 151 Lymphoma Cases].

OBJECTIVE: To analyze the influential factors related to mobilization and collection of stem cells so as to improve the collection efficiency of autologous peripheral stem cell transplantation in lymphoma patients. METHODS: The peripheral blood stem cell collection data of 151 cases of lymphoma in our hospital was analyzed retrospectively. The relationship between the harvested CD34(+) stem cells and some factors, such as age, sex, height, weight, histological type, staging, mobilization programs, collecting days, blood transfusion, time and duration of chemotherapy, was analyzed. RESULTS: The single factor analysis showed that sex, height, weight, histological type, staging, mobilization program, collecting days, blood transfusion were not significantly associated with CD34(+) stem cells collection, respectively. Age (r = -0.248, P = 0.002), duration of sick and cycles of chemotherapy were significantly associated with CD34(+) cell collection. At the age older than 50 years, the collected CD34(+) cell number decreased significantly; and at the age older than 60 years, the CD34(+) cell number was greatly reduced; CD34(+) cells non-significantly correlated with peripheral blood WBC (r = 0.053, P = 0.527), but significantly with the percentage of mononuclear cells (r = 0.260, P = 0.002) and the absolute value of mononuclear cells (r = 0.338, P = 0.00003) . CONCLUSION: The patients less than 60 years old, fewer chemotherapy cycles, shorter duration time or PB mononuclear cells between (2-6) × 10(9)/L may contribute to the better mobilization and collection of peripheral blood stem cells.

Bumetanide hyperpolarizes madin-darby canine kidney cells and enhances cellular gentamicin uptake by elevating cytosolic Ca(2+) thus facilitating intermediate conductance Ca(2+)--activated potassium channels.

Loop diuretics such as bumetanide and furosemide enhance aminoglycoside ototoxicity when co-administered to patients and animal models. The underlying mechanism(s) is poorly understood. We investigated the effect of these diuretics on cellular uptake of aminoglycosides, using Texas Red-tagged gentamicin (GTTR), and intracellular/whole-cell recordings of Madin-Darby canine kidney (MDCK) cells. We found that bumetanide and furosemide dose-dependently enhanced cytoplasmic GTTR fluorescence by ~60 %. This enhancement was suppressed by La(3+), a non-selective cation channel (NSCC) blocker, and by K(+) channel blockers Ba(2+) and clotrimazole, but not by tetraethylammonium (TEA), 4-aminopyridine (4-AP) or glipizide, nor by Cl(-) channel blockers diphenylamine-2-carboxylic acid (DPC), niflumic acid (NFA), and CFTRinh-172. Bumetanide and furosemide hyperpolarized MDCK cells by ~14 mV, increased whole-cell I/V slope conductance; the bumetanide-induced net current I/V showed a reversal potential (V r) ~-80 mV. Bumetanide-induced hyperpolarization and I/V change was suppressed by Ba(2+) or clotrimazole, and absent in elevated [Ca(2+)]i, but was not affected by apamin, 4-AP, TEA, glipizide, DPC, NFA, or CFTRinh-172. Bumetanide and furosemide stimulated a surge of Fluo-4-indicated cytosolic Ca(2+). Ba(2+) and clotrimazole alone depolarized cells by ~18 mV and reduced I/V slope with a net current V r near -85 mV, and reduced GTTR uptake by ~20 %. La(3+) alone hyperpolarized the cells by ~-14 mV, reduced the I/V slope with a net current V r near -10 mV, and inhibited GTTR uptake by ~50 %. In the presence of La(3+), bumetanide-caused negligible change in potential or I/V. We conclude that NSCCs constitute a major cell entry pathway for cationic aminoglycosides; bumetanide enhances aminoglycoside uptake by hyperpolarizing cells that increases the cation influx driving force; and bumetanide-induced hyperpolarization is caused by elevating intracellular Ca(2+) and thus facilitating activation of the intermediate conductance Ca(2+)-activated K(+) channels.

Dihydropyridines inhibit acetylcholine-induced hyperpolarization in cochlear artery via blockade of intermediate-conductance calcium-activated potassium channels.

Acetylcholine (ACh) induces hyperpolarization and dilation in a variety of blood vessels, including the cochlear spiral modiolar artery (SMA) via the endothelium-derived hyperpolarization factor (EDHF). We demonstrated previously that the ACh-induced hyperpolarization in the SMA originated in the endothelial cells (ECs) by activating a Ca(2+)-activated K(+) channel (K(Ca)); the hyperpolarization in smooth muscle cells was mainly an electrotonic spread via gap junction coupling. In the present study, using intracellular recording, immunohistology, and vascular diameter tracking techniques on in vitro SMA preparations, we found that 1) ACh-induced hyperpolarization was suppressed by intermediate-conductance K(Ca) (IK) blockers clotrimazole (IC(50) = 116 nM) and nitrendipine and by the calmodulin antagonist trifluoperazine, but it was not suppressed by the big-conductance K(Ca) blocker iberiotoxin. The immunoreactivity to anti-SK4/IK1 antibody was localized mainly in ECs. 2) The three dihydropyridines--nifedipine, nitrendipine, and nimodipine--all concentration-dependently inhibited the ACh-induced hyperpolarization, with an IC(50) value of 455, 34, and 3.2 nM, respectively. 3) Among other L-type Ca(2+) channel (I(L)) blockers, 10 microM verapamil exerted a 20% inhibition on ACh-induced hyperpolarization, whereas diltiazem and the metal ion Ca(2+) channel blockers Cd(2+) and Ni(2+) had no effect. 4) Nitrendipine and charybdotoxin abolished ACh-induced dilation in the SMA. We conclude that ACh-induced hyperpolarization in the SMA is generated mainly by activation of the IK in the ECs, and dihydropyridines suppress the EDHF-mediated hyperpolarization by blocking the IK channel, not the I(L) channel. The clinical relevance of this dihydropyridine action is discussed.

Electrical coupling and release of K+ from endothelial cells co-mediate ACh-induced smooth muscle hyperpolarization in guinea-pig inner ear artery.

The physiological basis of ACh-elicited hyperpolarization in guinea-pig in vitro cochlear spiral modiolar artery (SMA) was investigated by intracellular recording combined with dye labelling of recorded cells and immunocytochemistry. We found the following. (1) The ACh-hyperpolarization was prominent only in cells that had a low resting potential (less negative than -60 mV). ACh-hyperpolarization was reversibly blocked by 4-DAMP, charybdotoxin or BAPTA-AM, but not by N(omega)-nitro-L-arginine methyl ester, glipizide, indomethacin or 17-octadecynoic acid. (2) Ba(2)(+) (100 microm) and ouabain (1 microm) each attenuated ACh-hyperpolarization by approximately 30% in smooth muscle cells (SMCs) but had only slight or no inhibition in endothelial cells (ECs). A combination of Ba(2)(+) and 18beta-glycyrrhetinic acid near completely blocked the ACh-hyperpolarization in SMCs. (3) High K(+) (10 mm) induced a smaller hyperpolarization in ECs than in SMCs, with an amplitude ratio of 0.49 : 1. Ba(2)(+) blocked the K(+)-induced hyperpolarization by approximately 85% in both cell types, whereas ouabain inhibited K(+)-hyperpolarization differently in SMCs (19%) and ECs (35%) and increased input resistance. 18beta-Glycyrrhetinic acid blocked the high K(+)-hyperpolarization in ECs only. (4) Weak myoendothelial dye coupling was detected by confocal microscopy in cells recorded with a propidium iodide-containing electrode for longer than 30 min. A sparse plexus of choline acetyltransferase-immunoreactive (ChAT) fibres was observed around the SMA and its up-stream arteries. (5) Evoked excitatory junction potentials (EJP) were partially blocked by 4-DAMP in half of the cells tested. We conclude that ACh-induced hyperpolarization originates from ECs via activation of Ca(2)(+)-activated potassium channels, and is independent of the release of NO, cyclo-oxygenase or cytochrome P450 products. ACh-induced hyperpolarization in smooth muscle cells involves two mechanisms: (a) electrical spread of the hyperpolarization from the endothelium, and (b) activation of inward rectifier K(+) channels (K(ir)) and Na(+)-K(+) pump current by elevated interstitial K(+) released from the endothelial cells, these being responsible for about 60% and 40% of the hyperpolarization, respectively. The role ratio of K(ir) and pump current activation is at 8 : 1 or less.