Solid-Phase synthesis of a library constructed of aromatic phosphate, long alkyl chains and tryptophane components, and identification of potent dipeptide telomerase inhibitors

Telomerase inhibitors are expected as a new candidate of therapeutic agents for cancer. Recently, we have found novel inhibitors based on the bisindole skeleton. In this study, solid-phase synthesis was applied to construct a library of inhibitors having aromatic phosphate, long alkyl chain and tryptophane components, from which a D,D-ditryptophane derivative has been identified as a new potent telomerase inhibitor with IC(50) values of 0.3 microM. A hypothetical binding model for the new inhibitors has been proposed based on the structure-activity relationship.

Development of novel telomerase inhibitors based on a bisindole unit

Telomerase is the enzyme that elongates telomere repeat at the ends of a chromosome. As high telomerase activity is observed in most cancer cells, inhibitors of human telomerase have been expected as new chemotherapeutic agents for cancer. We describe here the discovery of novel inhibitors with IC50 values in the submicromolar range. The structure of the novel inhibitors will be useful as a scaffold for construction of the library in the search for telomerase inhibitors.

Changes in cell volume induced by activation of the cyclic amp-dependent chloride channel in guinea-pig cardiac myocytes

The effects of the activation of cyclic AMP-dependent Cl- current (ICl,cAMP) on cell volume were studied at various [K+]o under isosmotic conditions in guinea-pig ventricular myocytes. The area of the cell image obtained with videomicroscopy was used as an index of cell volume. I(Cl,cAMP) was activated by adrenaline (5.5 microM). Measurements of the membrane potential (Vm) were performed by the gramicidin-perforated patch-clamp method. At 5.4 mM [K+]o with low [Cl-]o, where Vm was negative to the predicted equilibrium potential of Cl- (ECl), adrenaline sizably decreased the cell area. At high [K+]o with normal [Cl-]o, where Vm was positive to ECl, adrenaline increased the cell area; at 145.4 mM [K+]o the cell area was increased to 110% of control on average (n = 22). The cells swollen in this manner shrank when [Cl-]o was reduced to a low level in the presence of adrenaline. The results indicate that the induction of Cl- influxes (outward I(Cl,cAMP)) or effluxes (inward I(Cl,cAMP)) can lead to a cell swelling or shrinkage, respectively. The addition of BaCl2 (1 mm), a blocker of K+ channels, attenuated the adrenaline-dependent cell swelling, supporting the view that Cl- fluxes must be accompanied by cofluxes of K+ ions to affect the cell volume. The adrenaline-dependent cell swelling was inhibited by antagonizing beta-adrenergic stimulation with acetylcholine or by blocking I(Cl,cAMP) channels with glibenclamide, confirming the involvement of I(Cl,cAMP) in the adrenaline response. The results show that the activation of I(Cl,cAMP) can shrink or inflate the cardiac cells under isosmotic conditions, depending on Vm and ECl.

CyA-mediated renal interstitial and vascular lesions in the rat under low-sodium diet

Nephrotoxicity of CyA was analyzed histologically in rats fed a low-sodium diet. CyA was subcutaneously administered daily at a dose of 15 mg/kg for 10 or 35 days with or without prior uninephrectomy (UNT) in male Sprague-Dawley rats receiving a low-sodium diet (0.03% sodium). CyA-administered rats showed impaired renal function as well as tubulo-interstitial lesions, such as edema, tubular basement membrane changes, and tubular atrophy, in the cortex, especially in the subcapsular portion, within 10 days. On day 35, the tubulo-interstitial lesions were advanced with mild focal interstitial fibrosis. These lesions were mild in the UNT group compared to the non-UNT group. Immunohistochemically, CyA treatment caused an increase in number of renin-positive cells in the afferent arteriolar wall at juxtaglomerular area. These cells lost the expression of calponin, which is a marker of mature smooth muscle cells. In addition, in afferent arterioles and interlobular arteries, electron-dense fibrous bodies were found in the smooth muscle cells on days 10 and 35. Immunoelectron microscopically, these bodies showed scattered positive staining for calponin and alpha-actinin, were negative or only peripherally positive for alpha-SMA and vimentin, and were completely negative for desmin. This study revealed that CyA could cause interstitial lesions starting in the subcapsular portion of the renal cortex and vascular lesions of the preglomerular artery. Increases in number of renin granules and formation of cytoplasmic fibrous bodies in smooth muscle cells could be the forerunner of severe arteriolar wall damage.

Nodular lung disease with five year survival and unilateral pleural effusion in AL amyloidosis

A 67-year-old female patient with biopsy proven AL systemic amyloidosis developed rapidly progressive dyspnea. Chest roentgenogram and CT scan revealed a large right pleural effusion in addition to nodular lesions with bilateral hilar lymphadenopathy. The patient's serum showed IgG lambda type monoclonal gammopathy and she also had Bence Jones proteinuria. The pleural effusion was an exudate that contained many mononuclear cells and a high concentration of protein. Cardiac function was not seriously disturbed. Except for amyloidosis, no other causes for the severe pleural effusion were found. This patient was treated with chemical pleurodesis using Picibanil and a low dose of prednisolone. Eighteen months after this treatment, her right pleural effusion did not recur. Bronchopulmonary tissues are known to be frequently involved by AL systemic amyloidosis, but a nodular pattern of pulmonary amyloid deposition and a unilateral large pleural effusion are rare clinical manifestations in this disease.

Sarcoidosis with membranous nephropathy and granulomatous interstitial nephritis

A 49-year-old woman, who had been diagnosed as sarcoidosis based on bilateral hilar lymphadenopathy and lung biopsy, presented increased serum creatinine and calcium concentrations. Renal biopsy showed the presence of interstitial nephritis with non-caseating epithelioid granuloma and focal membranous transformation. Therapy with prednisolone was effective in normalizing serum creatinine, serum calcium, serum angiotensin converting enzyme, and urine beta2 microglobulin, but these abnormalities reappeared after rapid withdrawal of prednisolone. This is a rare case of sarcoidosis manifested by both membranous nephropathy and granulomatous interstitial nephritis, and indicates the necessity of long-term treatment of corticosteroid.

Molecular mechanism for pore-formation in lipid membranes by the hemolytic lectin CEL-III from marine invertebrate Cucumaria echinata

The pore-forming activity of CEL-III, a Gal/GalNAc specific lectin from the Holothuroidea Cucumaria echinata, was examined using artificial lipid membranes as a model system of erythrocyte membrane. The carboxyfluorescein (CF)-leakage studies clearly indicated that CEL-III induced the formation of pores in the dipalmitoyl phosphatidyl choline (DPPC)-lactosyl ceramide (LacCer) liposomes effectively but not in the DPPC-glucosyl ceramide (GlcCer) liposomes or DPPC liposomes. Such a leakage of CF was strongly inhibited by lactose, a potent inhibitor of CEL-III, suggesting that the leakage is mediated through the specific binding of CEL-III to the carbohydrate chains on the surface of the liposomes. The leakage of CF from the DPPC-lactosyl ceramide liposomes was pH-dependent, and it increased with increasing pH. The immunoblotting analysis and circular dichroism data indicated that upon interaction with liposomes, CEL-III associated to form an oligomer concomitantly with a marked conformational change. Furthermore, channel measurements showed that CEL-III has an ability to form small ion channels in the planar lipid bilayers consisting of diphytanoylphosphatidylcholine and human globoside (Gb4Cer)/LacCer.

On the mechanism of the enhancement of delayed rectifier K+ current by extracellular ATP in guinea-pig ventricular myocytes

The effects of extracellular adenosine 5'-triphosphate (ATP) on the delayed rectifier K+ current (IK) were studied in guinea-pig ventricular myocytes using the whole-cell voltage-clamp technique. ATP increased IK concentration dependently with a concentration eliciting a half-maximal response of 1.86 microM and a maximal increase of about 1.8-fold. The enhancement of IK developed slowly, the effect reaching a maximum in about 1.6 min after application of ATP. The rank order of agonist potency in enhancing IK was 2-methylthio-ATP>/= ATP>>alpha,beta-methylene-ATP. The ATP response was attenuated in guanosine 5'-O-(2-thiodiphosphate) (GDPbetaS)- loaded cells, but was not affected by pertussis toxin (PTX)-pre-treatment, indicating that a PTX-insensitive G protein is involved in the response. These features are consistent with operation of P2Y-type purinoceptors. ATP produced a further increase in IK stimulated maximally either by isoprenaline (1 microM) through protein kinase A (PKA) or by 12-O-tetradecanoylphorbol 13-acetate (TPA, 100 nM) through protein kinase C (PKC), while 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7, 10 microM) did not affect the ATP response, suggesting that PKA and PKC do not mediate the response. ATP irreversibly enhanced IK in cells loaded with adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS, 5 mM) or okadaic acid (10 microM), a phosphatase inhibitor, suggesting that a phosphorylation step is present after the receptor stimulation. Genistein, an inhibitor of tyrosine phosphorylation, suppressed the ATP response significantly, while daidzein, an inactive analogue of genistein, had little effect on it, although both genistein or daidzein alone decreased IK. It is hypothesized that tyrosine phosphorylation plays a role in the signalling pathway involved in the enhancement of cardiac IK by P2Y-purinergic stimulation.

Enzyme level of enterococcal F1Fo-ATPase is regulated by pH at the step of assembly

The amount of F1Fo-ATPase in Enterococcus hirae (formerly Streptococcus faecalis) increases when the cytoplasmic pH is lowered below 7.6, and protons are extruded to maintain the cytoplasmic pH at around 7.6. In the present study, we found that the transcriptional activity of the F1Fo-ATPase operon was not regulated by pH. The synthesis of F1 subunits was increased 1.65 +/- 0.12-fold by the acidification of medium from pH 8.0 to pH 5.3. Western-blot analysis showed that there were F1 subunits in the cytoplasm, and the number of alpha plus beta subunits in the cytoplasm was 50% of the total number of the subunits in cells growing at pH 8.0. This decreased to 22% after shifting the medium pH to 5.3, with a concomitant 5.1-fold increase in the level of membrane-bound F1Fo-ATPase. The cytoplasmic F1 subunits were shown to be degraded, and Fo subunits not assembled into the intact F1Fo complex were suggested to be digested. These data suggest that regulation of the enzyme level of F1Fo-ATPase by the intracellular pH takes place mainly at the step of enzyme assembly from its subunits.

Contribution of mast cells to the tubulointerstitial lesions in IgA nephritis

BACKGROUND

Mast cells have never been extensively investigated in renal disease, particularly glomerulonephritis. Recent improvements in monoclonal antibody production to mast cell specific enzymes have made it possible to study mast cells in tissues more accurately and easily. Mast cells have been found to secrete basic fibroblast growth factor (bFGF) in human pulmonary fibrosis.

METHODS

Mast cells in 67 cases of IgA nephritis were investigated. Toluidine blue (TB) stainings at pH 5.0 and pH 0.5 were employed histochemically, and anti-human mast cell tryptase and chymase monoclonal antibodies were used immunohistochemically. Anti-bFGF antibody was also used immunohistochemically.

RESULTS

Mast cells were scattered in the interstitium including in fibrotic areas. TB pH 0.5-positive mast cells were more numerous than TB pH 5. 0-positive mast cells. Immunostaining with anti-tryptase monoclonal antibody detected more mast cells than the TB stainings. Mast cells in the interstitium of IgA nephritis had both tryptase and chymase. Immunoelectron microscopy showed that tryptase was exclusively localized in the specific granules of mast cells. The average number of tryptase positive mast cell in the interstitium of IgA nephritis was lower than that of T lymphocyte but more than that of macrophages. The average number of mast cells increased with the progression of interstitial fibrosis and had a significant correlation with 24-hour creatinine clearance. Using double labeled immunohistochemistry, some tryptase-positive mast cells had bFGF in their cytoplasm. Electron microscopy showed that mast cells were associated with fibroblasts and/or lymphocytes in the interstitium.

CONCLUSION

Mast cells are one of the constitutive cells in the interstitium of IgA nephritis patients and affect renal function by contributing to the interstitial fibrosis.

A repolarization-induced transient increase in the outward current of the inward rectifier K+ channel in guinea-pig cardiac myocytes

1. Outward currents of the inwardly rectifying K+ current (IKir) in guinea-pig ventricular myocytes were studied in the presence of 1 mM intracellular free Mg2+ using the whole-cell patch-clamp technique. 2. During repolarizing voltage steps following a large depolarizing pulse (> 0 mV), outward IKir increased transiently at voltages positive to the K+ equilibrium potential (EK, -84 mV for 5.4 mM extracellular [K+]). The rising phase was almost instantaneous, while the decay was exponential. The decay rate was faster at voltages closer to EK (time constants, 33.9 +/- 9.8 and 4.8 +/- 1.4 ms at -30 and -50 mV, respectively). 3. The transient outward IKir was absent when the preceding depolarization was applied from -40 mV. Larger transient currents developed as the voltage before the depolarization was shifted to more hyperpolarized levels. 4. Shift of the depolarizing voltage from > 0 mV to more negative ranges diminished the amplitudes of transient outward IKir and instantaneous inward IKir during the subsequent repolarizing steps positive and negative to EK, respectively. Since blockage of IKir by internal Mg2+ occurs upon large depolarization, and the block is instantaneously relieved at voltages negative to EK, the rising phase of the transient outward IKir was attributed to the relief of Mg2+ block at voltages positive to EK. Transient outward IKir was absent when intracellular [Mg2+] was reduced to 10 microM or lower. 5. Prolongation of the repolarizing voltage step increased the amplitude of time-dependent inward IKir during the subsequent hyperpolarization, indicating the progress of a gating process (presumably the channel block by intracellular polyamine) during the decaying phase of outward IKir. 6. Progressive prolongation of the depolarizing pulse (> 0 mV) from 100 to 460 ms decreased the transient outward IKir amplitude during the subsequent repolarizing step due to slow progress of the gating (polyamine block) at > 0 mV. 7. Current-voltage relations measured using repolarizing ramp pulses (-3.4 mV ms-1) showed an outward hump at around -50 mV, the magnitude of which increased as the voltage before the conditioning depolarization (10 mV) was shifted to more negative levels. With slower ramp speeds (-1.5 and -0.6 mV ms-1), the hump was depressed at voltages near EK. 8. Our study suggests that the relief of Mg2+ block may increase outward IKir during repolarization of cardiac action potentials, and that the resting potential, the level/duration of action potential plateau and the speed of repolarization influence the outward IKir amplitude. 9. A kinetic model incorporating a competition between polyamine block and Mg2+ block was able to account for the time dependence of outward IKir.

Intracellular Mg2+ depletion depresses the delayed rectifier K+ current in guinea pig ventricular myocytes

The effects of various [Mg2+]i, particularly low [Mg2+]i, on the delayed rectifier K+ current (IK) were studied in guinea pig ventricular myocytes with the patch clamp technique. The magnitude of IK was evaluated from the amplitude of its tail current elicited on repolarization following the depolarizing steps. The pipette-perfusion technique was also used. The initial variations of IK magnitude were dependent on [Mg2+]i in the internal solutions with which the whole-cell recording was begun. With 0.03 to 1 mM [Mg2+]i, IK was relatively stable after patch rupture, showing a minimal decay with time; with 3 mM [Mg2+]i, IK rapidly declined; with [Mg2+]i, less than 0.01 mM IK transiently increased after patch break, but declined progressively thereafter as the magnitude of IK decreased to about 30% of the initial magnitude in 10 min. The decline of IK at low [Mg2+]i showed the following features. The decline was accompanied little by changes in the voltage-activation relation or by changes in the kinetics of current deactivation. The decline was not related to changes in [Ca2+]i and was also observed in ATP gamma S-loaded, isoprenaline-stimulated cells, in which IK channels were presumed to be persistently phosphorylated. An application of okadaic acid did not prevent the decline of IK during Mg2+ depletion. It is suggested that a presence of [Mg2+]i higher than 0.01 mM is required to maintain IK in guinea pig ventricular cells. The depression of IK at low [Mg2+]i appears to involve a phosphorylation-dephosphorylation-independent mechanism.

Swelling-induced Cl- current in guinea-pig atrial myocytes: inhibition by glibenclamide

1. Whole-cell currents were recorded from guinea-pig atrial myocytes using the patch-clamp technique under conditions designed to block K+ channels, Ca2+ channels and electrogenic transporters. 2. Exposure of atrial myocytes to the hyposmotic external solution (Na+ reduction to about 70% of control) resulted in hyposmotic cell swelling which was associated with activation of an outwardly rectifying Cl- current (ICl,swell). 3. Whereas the activation of ICl,swell was not significantly affected by replacement of ATP in the pipette solution with the non-hydrolysable ATP analogue 5'-adenylyl-imidodiphosphate (AMP-PNP), its activation was greatly reduced in cells dialysed with an ATP-free pipette solution, thus indicating that the activation process of ICl,swell requires the presence of intracellular ATP, but not its hydrolysis. 4. Bath application of glibenclamide produced a concentration-dependent block of ICl,swell with a half-maximal inhibitory concentration (IC50) of 60.0 microM and a Hill coefficient of 2.1. The maximal effect (100% inhibition) was obtained with 500 microM glibenclamide. The steady-state inhibition showed little voltage dependence, while glibenclamide at concentrations of more than 100 microM inhibited the outward ICl,swell more rapidly than the inward ICl,swell. The glibenclamide inhibition was fully reversible after removal of the drug, even when a maximal effect (full inhibition) was achieved at a high drug concentration (500 microM). 5. These results show that (i) glibenclamide is one of the most potent inhibitors of guinea-pig atrial ICl,swell, and (ii) atrial ICl,swell and the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- currents are almost equally sensitive to inhibition by glibenclamide.

Selective enhancement of the slow component of delayed rectifier K+ current in guinea-pig atrial cells by external ATP

1. The effects of external ATP on the rapidly and slowly activating components (IKr and IKs, respectively) of the delayed rectifier K+ current (IK) in guinea-pig atrial myocytes were determined using the whole-cell configuration of the patch-clamp technique. 2. An envelope of tails test was conducted by applying depolarizing pulses to +40 mV from a holding potential of -40 mV for various durations between 50 ms and 2 s under control conditions and during exposure to 50 microM ATP. The ATP-induced IK, obtained by digital subtraction, exhibited a constant ratio (0.37) of the tail current to time-dependent current, regardless of the pulse duration. This current ratio was compatible with the predicted ratio of the driving force at +40 and -40 mV for a non-rectifying K+ conductance, suggesting that the ATP-induced IK is due primarily to IKs. 3. The amplitude of IKr isolated from the IK enhanced by ATP, determined as an E-4031 (5 microM)-sensitive current, was similar to the control magnitude of IKr, thus showing that external ATP did not cause an increase in IKr. 4. The voltage-dependent activation of the ATP-induced IK during 500 ms depolarizing test pulses could be described by a Boltzmann equation with a half-activation voltage (V1/2) of 11.5 mV and slope factor (k) of 12.0 mV, which were close to those of IKs (V1/2 of 12.1 mV and k of 12.3 mV), determined as an E-4031-resistant IK, under the same isochronal (500 ms) activation conditions. 5. These results provide evidence to suggest that extracellular ATP selectively potentiates the slow component of IK (IKs), with no measurable effects on IKr, in guinea-pig atrial myocytes.

Modulation of the muscarinic K+ channel by P2-purinoceptors in guinea-pig atrial myocytes

1. Activation of muscarinic K+ (KACh) channels by P2-purinergic agonists, such as ATP, decreases monotonically in the continued presence of agonist. We investigated the mechanisms underlying this process of decline in guinea-pig atrial myocytes using the patch-clamp technique. 2. External ATP reversibly depressed the acetylcholine (ACh, 5.5-11 microM)-induced KACh current in a concentration-dependent manner with a half-maximal inhibitory concentration (IC50) of 5.4 microM. 3. External ATP irreversibly reduced guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S)-induced KACh current both in control and pertussis toxin (PTX)-pretreated cells, suggesting (i) that the ATP-induced inhibition of KACh current occurred at some step(s) downstream from the activation of the PTX-sensitive G protein, GK, and (ii) that a PTX-insensitive G protein was involved in the signal transduction pathway. 4. The potency order of ATP analogues in reducing KACh current was ATP > or = 2-methylthio-ATP > or = alpha, beta-methylene-ATP, indicating involvement of a P2Y-type purinoceptor. 5. In the cell-attached patch recording, ATP (100 microM) applied to the bath solution reduced the activity of the KACh channels activated by ACh in the pipette, in two out of eight experiments, suggesting the possible involvement of cytosolic second messengers in the inhibition of KACh channels. 6. The ATP-induced reduction of KACh current was not affected by a protein kinase C inhibitor, 1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydrochloride (H-7), suggesting that this response was not mediated by the activation of protein kinase C. 7. These results demonstrate that, in addition to the membrane-delimited activation through GK, external ATP causes an inhibition of the KACh channel probably by activating a PTX-insensitive G protein and cytosolic second messenger(s), which may underlie the monotonic decrease of the ATP-activated KACh current.

Microwave continuous sterilization of injection ampoules

A new microwave continuous sterilizer (MWS) for applying microwave dielectric heating as an alternative to an autoclave was developed. The developmental objectives of the MWS were: 1. Achieving sufficient sterilization for the drugs containing heat-sensitive ingredients. 2. Measuring and recording sterilization temperature of each ampoule. 3. Ensuring automatic continuous operation and linkage with the preceding and following machines in an injection ampoule production process. The temperature of the drug solution in an ampoule was heated to 140 degrees C within about 30 seconds by the MWS. Target F0 value is achieved through the maintaining heater to maintain the target temperature for 12 seconds. Ampoules are cooled with air and water after completion of heating. The MWS is capable of processing 150 ampoules per minute. The newly developed techniques which minimized temperature distribution of heated ampoule solution were: 1. Microwave irradiation in a direction opposite to the direction of ampoules transportation. 2. Microwave irradiation in the lower part of ampoule solution (i.e., heating up the drug solution by thermal convection.) 3. Microwave power control by feedback of measured temperatures. 4. Heating rate control corresponding to the dielectric property of ampoule solution. The drug stability test was performed using 3% pyridoxamine phosphate solution, and the inactivation of spores in 3% pyridoxamine phosphate solution was examined using Bacillus stearothermophilus ATCC 7953 spores. The MWS was proved to have an adequate efficiency of sterilization with less chemical degradation of the contents than an autoclave.

Cervical Castleman's disease associated with benign M-proteinemia: report of a case

We report the unusual case of a 77-year-old man with cervical Castleman's disease associated with benign M-proteinemia. The patient was found to have an anterior cervical tumor during a follow-up examination after surgery for early gastric cancer, at which time blood biochemistry tests revealed M-proteinemia at the position of beta-globulin with a high level of IgG and low levels of IgA and IgM. Serum protein immunoelectrophoresis revealed M-protein consisting of the IgG-k chain, and urine protein immuno-electrophoresis demonstrated Bence Jones protein consisting of the chain. No abnormalities were noted in bone marrow aspiration or bone scintigram. The results of imaging and fine-needle aspiration biopsy of the tumor led to a pre-operative diagnosis of cervical malignant lymphoma with suspected M-proteinemia derived from this disease, and resection of the anterior cervical tumor with bilateral neck dissection was performed. Histopathological examination subsequently demonstrated four mixed-type tumors of Castleman's disease. The pathogenesis of Castleman's disease remains unknown; however, we speculate that the complication of benign M-proteinemia in this patient was not incidental, but caused by an underlying immunological abnormality of the B cells.

Total synthesis of VIM-2 ganglioside isolated from human chronic myelogenous leukemia cells

A total synthesis of the tumor-associated glycolipid antigen, VIM-2, is described [2]. Phenyl 2,3,4-tri-O-benzoyl-6-O-benzyl-beta-D-galactopyranosyl-(1-->4)-6-O-benzy l-2- deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside (7), a key intermediate prepared by condensation of phenyl 6-O-benzyl-2-deoxy-2-phthalimido-1-thio-beta-D-glucopyranoside (6) and 2,3,4-tri-O-benzoyl-6-O-benzyl-alpha-D-galactopyranosyl bromide (5), was glycosylated with methyl 2,3,4-tri-O-benzyl-1-thio-beta-L-fucopyranoside (8) to give the trisaccharide donor 9, which, on coupling with 2-(trimethylsilyl)ethyl 2,4,6-tri-O-benzyl-beta-D-galactopyranosyl-(1-->4)-2,3,6-tri-O-benzyl-be ta-D- glucopyranoside (10), afforded the pentasaccharide 11. The regioselective glycosylation of 12 (derived by O-debenzoylation of 11) with 7 gave the heptasaccharide 13, which was converted by treatment with hydrazine monohydrate and subsequent N-acetylation into the hexasaccharide acceptor 14. The stereo- and regio-selective glycosylation of 14 with methyl (phenyl 5-acetamido-4,7,8,9-O-benzoyl-3,5-dideoxy-2-thio-D-glycero-beta-D-galact o-2- nonulopyranosid)onate (16) gave the desired octasaccharide 18. Hydrogenolytic removal of the benzyl groups in 18 and successive O-acetylation, removal of the 2-(trimethylsilyl)ethyl group, and treatment with trichloroacetonitrile gave the alpha-trichloro-acetimidate 21, which was then coupled with (2S,3R,4E)-2-azido-3-O-(tert-butyldiphenylsilyl)-4-octade cene-1,3-diol (22) to give 23. Compound 23 was transformed, via selective reduction of the azido group, N-introduction of octadecanoic acid, O-desilylation, O-deacylation, and saponification of the methyl ester group, into the title VIM-2 ganglioside 26.

Activation of the muscarinic K+ channel by P2-purinoceptors via pertussis toxin-sensitive G proteins in guinea-pig atrial cells

1. Whole-cell voltage clamp and cell-attached patch-clamp techniques were applied to single atrial myocytes enzymatically dissociated from adult guinea-pig hearts. 2. In whole-cell clamp conditions, external applications, of ATP activated the muscarinic K+ (KACh) current, identified by its inward rectification, its reversal potential near the calculated K+ equilibrium potential (EK) and its relaxation properties during step changes of whole-cell membrane potential. Theophylline, an antagonist for Pi-purinoceptors, did not affect the action of ATP on the KACh current, indicating that the response was evoked through P2-purinoceptors. 3. The concentration-response relationship for ATP was well described by a Hill equation with a half-maximal concentration of 1.84 microM and a Hill coefficient of 0.94. ATP (100 microM) produced a maximal increase of the KACh current to 10.92 microA microF-1, which corresponds to 44.9 and 80.9% of the maximal increases evoked by ACh (10 microM) and adenosine (100 microM), respectively. 4. The activation of KACh current gradually declined to a steady level despite the continuous presence of ATP (desensitization). Recovery from the desensitization was relatively rapid with a half-time of approximately 1.5 min. 5. The activation of KACh current by ATP was completely abolished by pre-incubating myocytes with pertussis toxin (PTX, 5 micrograms ml-1), indicating that P2-purinoceptors are coupled to PTX-sensitive G proteins to activate the KACh channel. 6. In the cell-attached patch recording, ATP (5 microM) applied to the pipette solution enhanced the activity of a channel with single-channel conductance of 52.7 +/- 0.9 pS (mean +/- S.E.M., n = 10), reversal potential near EK and mean open time of 1.1 +/- 0.1 ms. These conductance and kinetic properties are identical to those of the KACh channel in the heart. In contrast, ATP applied to the bath solution did not significantly affect the basal activity of KACh channel openings. These observations suggest that the mechanism coupling the P2-purinoceptor to the activation of the KACh channel involves membrane-delimited component(s) rather than soluble second messenger(s). 7. These results strongly suggest a direct coupling of the P2-purinoceptor to the KACh channel through PTX-sensitive G proteins, analogous to the coupling mechanism of the muscarinic ACh receptor and Pi-purinoceptor to this channel.

Enhancement of delayed rectifier K+ current by P2-purinoceptor stimulation in guinea-pig atrial cells

1. We studied the effects of P2-purinoceptor stimulation on the delayed rectifier K+ current (IK) in guinea-pig atrial myocytes using a whole-cell voltage-clamp technique. 2. External application of ATP increased IK, evoked by a 500 ms depolarizing pulse from a holding potential of -40 mV, under conditions in which the L-type Ca2+ channel was blocked; the effect was dose dependent with a half-maximal concentration (K1/2) of 0.95 microM. ATP (50 microM) produced a maximal increase of IK of about a factor of 2. 3. External ADP also enhanced IK in a dose-dependent manner with a K1/2 of 3.65 microM, whereas adenosine (100 microM) failed to evoke this response. Theophylline (500 microM), a blocker of the Pi-purinoceptor, did not antagonize the stimulating action of ATP on IK. These results indicate that IK was enhanced via P2-purinoceptors. 4. External ATP or ADP did not produce a significant change in the current kinetics of IK. 5. Pre-incubation of the atrial myocytes with pertussis toxin (PTX, 5 micrograms ml-1) did not affect the stimulating action of ATP on IK, indicating that PTX-sensitive G proteins did not mediate the ATP action. 6. The enhancement of IK by ATP developed slowly; the effects usually reached a maximum approximately 30-60 s after the application of ATP. This suggests the involvement of a diffusible cytosolic second messenger(s) in the response. ATP could further increase IK after maximal enhancement by isoprenaline (0.5-1.0 microM), suggesting that the intermediate steps were independent of cyclic AMP-dependent protein kinase (protein kinase A). 7. Potentiation of IK by ATP was not attenuated by either (i) pretreatment of the cells with 5 microM 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine dihydrochloride (H-7) or (ii) intracellular perfusion of 20 mM 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), suggesting that protein kinase C and intracellular Ca2+ did not mediate the response. 8. It is concluded that the activation of P2-purinoceptors increases IK through intracellular mechanisms independent of protein kinase A, protein kinase C or intracellular free Ca2+ in guinea-pig atrial myocytes.

alpha-Adrenergic inhibition of the beta-adrenoceptor-dependent chloride current in guinea-pig ventricular myocytes

1. alpha 1-Adrenoceptor-mediated inhibition of the beta-adrenoceptor-dependent Cl- current was investigated in guinea-pig ventricular myocytes using the patch clamp technique. The Cl- conductance activated by noradrenaline (0.1-10 microM) with an alpha 1-blocker (prazosin, 5 microM) was significantly greater than that activated by noradrenaline alone. Phenylephrine and methoxamine, alpha 1-agonists, exerted an inhibitory effect on the Cl- conductance activated by isoprenaline. The dose-response relationship for isoprenaline and the Cl- current activation was shifted to higher doses in the presence of phenylephrine (30 microM). 2. The interaction of alpha 1- and beta-agonists on Cl- current was also observed on the single channel level; in some of the outside-out membrane patches, phenylephrine (50 microM) depressed the activity of the single Cl- channel which was induced by 5 microM adrenaline. 3. Phenylephrine had no effect on the Cl- conductance induced by forskolin (0.5-5 microM), an activator of adenylate cyclase. The Cl- conductance activated persistently by isoprenaline in GTP gamma S-loaded cells was also insensitive to phenylephrine. The results suggest that the observed alpha 1-adrenergic attenuation of the beta-adrenergic response is not primarily due to inhibition of adenylate cyclase activity. The alpha 1-adrenergic action may interfere with the processes leading to enzyme activation in the beta-adrenergic pathway.

Purification and some properties of S-Hemolysin produced by Streptomyces sp. strain no. A-6288

A new cytolytic toxin, designated as S-Hemolysin, was found in the culture filtrate of Streptomyces sp. strain No. A-6288, isolated from a soil sample. The molecular weight of S-Hemolysin was estimated to be 10,000 by SDS-polyacrylamide gel electrophoresis and to be 20,000 by Sephadex G-100. S-Hemolysin is a glycoprotein that is composed of 102 amino acid residues with 11.6% glucose, and the isoelectric point is around pH 5.8. The phospholipase C activity of S-Hemolysin was specific for the following substrates in this order: sphingomyelin > lysophosphatidylethanolamine > lysophosphatidylcholine > phosphatidylethanolamine > phosphatidylcholine. S-Hemolysin had hemolytic activity against rabbit, human, and sheep erythrocytes, but did not cause aggregation of human platelets. These activities were accelerated with Mg2+, Mn2+, and Co2+ ions and inhibited by the addition of Ca2+, Cu2+, and Zn2+ ions. This enzyme was shown to be different from the known bacterial phospholipase C.

Isolation and characterization of mutants affected in lipid metabolism of Chlamydomonas reinhardtii

Two mutants affected in lipid metabolism of Chlamydomonas reinhardtii were isolated by treating cells with ultraviolet light. Both mutants showed high chlorophyll fluorescent yields, as compared with parents, and were designated as hf-2 and hf-9 (for high fluorescence). hf-2 was shown to be defective in the synthesis of a chloroplast-specific lipid, sulfoquinovosyl diacylglycerol. hf-9 was shown to be defective in desaturation at the omega 6 position of fatty acids of monogalactosyl diacylglycerol, digalactosyl diacylglycerol, sulfoquinovosyl diacylglycerol and phosphatidylglycerol. The mutants exhibited alterations in photosynthetic activity and chloroplast ultrastructure.