Complex effects of inhibitors on cyclic GMP-stimulated cyclic nucleotide phosphodiesterase

We have investigated the effects of several phosphodiesterase inhibitors on the activity of a cGMP-stimulated cyclic nucleotide phosphodiesterase purified from calf liver supernatant. Theophylline, RO 20-1724, and MY 5445 were not effective inhibitors. With 0.5 microM [3H]cGMP as substrate or with 0.5 microM [3H]cAMP in the presence of 1 microM cGMP, activity was inhibited by papaverine, dipyridamole, isobutylmethylxanthine (IBMX), and cilostamide. With 0.5 microM [3H]cAMP as substrate, however, only cilostamide was inhibitory; papaverine, dipyridamole, and IBMX increased activity. The increase was dependent on both drug and substrate concentration with maximal stimulation (150-180%) at concentrations of cAMP between 0.5 and 2.5 microM. At higher cAMP concentrations, the three drugs were inhibitory; inhibition was maximal at approximately 40 microM and decreased at higher cAMP concentrations. Inhibition of cGMP hydrolysis was maximal at approximately 3 microM and decreased at higher concentrations. Papaverine, IBMX, dipyridamole, and cilostamide inhibited [3H] cGMP hydrolysis competitively with Ki values of 3, 6.5, 7, and 11.5 microM, respectively. Papaverine, IBMX, or dipyridamole reduced the Hill coefficient for cAMP hydrolysis from 1.8 to 1.1-1.2, and Lineweaver-Burk plots were linear or nearly linear. With cilostamide, however, Lineweaver-Burk plots remained curvilinear. Thus, three competitive inhibitors, papaverine, dipyridamole, and IBMX, can mimic substrate and effect allosteric transitions that increase catalytic activity, whereas another, cilostamide, apparently cannot. Differences in the actions of these inhibitors presumably reflect differences in the molecular requirements for effective interaction at catalytic and allosteric sites on phosphodiesterase, i.e. differences in the structure of these sites.     

Effects of W-7 on catecholamine release and 45Ca2+ uptake in cultured adrenal chromaffin cells.

Effects of N-(6-aminohexyl)-5-chloro-1-naph-thalenesulfonamide (W-7), a calmodulin antagonist, on catecholamine (CA) release and ⁴⁵Ca²⁺ uptake were studied using cultured bovine adrenal chromaffin cells. W-7 inhibited the carbamylcholine (CCh)-evoked CA release and ⁴⁵Ca²⁺ uptake in a concentration-dependent manner. The inhibitory effect of W-7 on CCh-evoked CA release was not overcome either by an increase in extracellular calcium or CCh concentration. Although W-7 inhibited the high K⁺-evoked CA release and ⁴⁵Ca²⁺ uptake, potency of the drug was approximately 50–100 fold less than when inhibiting the CCh-evoked CA release and ⁴⁵Ca²⁺ uptake. The inhibitory effects of W-7 were observed both in norepinephrine release and epinephrine release. Moreover, W-7 inhibited the CCh-evoked ⁴⁵Ca²⁺ efflux. These results suggest that the inhibition of CA release by W-7 in adrenal chromaffin cells is mainly due to its inhibition of calcium uptake. W-7 may influence the linkage between acetylcholine-receptor and calcium uptake with higher potency than depolarization-dependent calcium entry.     

Cadaverine Involved in Urate Degrading Activity (Uricase Activity) in Soybean Radicles

Cadaverine, a 5-carbon diamine, was identified as the cofactorof uricase activity previously found in soybean seedlings. Thesubstance purified from freeze dried hypocotyls was subjectedto liquid chromatography, mass spectrometry, ¹H- and ¹³C-nuclearmagnetic resonance spectrometry for identification. The concentrationsof cadaverine in 3-day-old radicles and hypocotyls were 2.37mM and 5.09 mM, respectively. Other polyamine concentrationswere low. Biogenic polyamines (cadaverine, putrescine, spermidineand spermine) functioned as cofactors, whereas conjugated polyamines(tyramine and histamine) and amino acids had no effect. Theaddition of catalase to the assay system counteracted the effectof cadaverine. Peroxide at appropriate concentrations actedlike cadaverine with an identical K_m value, suggesting thaturate degrading activity can be ascribed to the diamine oxidase-peroxidasesystem. (Received October 19, 1982; Accepted December 23, 1982)     

An inducible lactone hydrolase yielding 2,5-diphenyl-3-hydroxy-4-oxo-2-hexendioic acid from pulvinic acid

The metabolism of vulpinic acid by an unclassified soil micro-organism was studied. A new compound, 2,5-diphenyl-3-hydroxy-4-oxo-2-hexendioic acid (DHOHA) was isolated from the reaction mixture of a cell-free preparation and pulvinic acid. The existence of a hydrolase which catalyses the conversion of vulpinic acid to pulvinic acid was detected in cell-free preparation, and an inducible lactone hydrolase capable of converting pulvinic acid to DHOHA was purified 130-fold and characterized. This enzyme had a MW of ca 34 000, a K_m for pulvinic acid at pH optimum (pH 7.0) less than 10 ^{? 6} M, pI = 5.0, and was inhibited by p-chloromercuriphenylsulfonate and diethylpyrocarbonate. The enzyme was highly specific for pulvinic acid. The initial degradative steps proposed for this organism are vulpinic acid → pulvinic acid → DHOHA.     

Whole body autoradiographic distribution of exogenously administered renin in mice

The distribution of exogenously administered renin was investigated using whole body autoradiography. Purified renin from mouse submaxillary gland (SR) was labeled with radioactive iodine (125I). This labeled renin (125I-SR) and Na125I were administered into the tail vein of male ddY mice, in doses of 10.2 and 16.4 mu Ci/30 g body weight, respectively. Mice were killed by an overdose of ether, and autoradiography was performed on whole body sections. To separate free 125I liberated from 125I-SR, sections were treated with perchloric acid. A major accumulation of 125I-SR, acid-insoluble, was evident in the renal cortex, whereas the hepatic accumulation of 125I-SR was minor. Radioactivity in the thyroid and submaxillary glands, in the stomach, and in urine was also apparent, but disappeared after acid treatment, except in the thyroid glands. Radioactivity in the brain, intestinal content, spleen, and adrenal glands was nil. These autoradiograms provide the first evidence that exogenously administered renin is mainly distributed in the renal cortex.     

Suppressive effect of human natural killer cells on pokeweed mitogen-induced B cell differentiation

The suppressive effect of human natural killer (NK) cells on B cell differentiation induced by pokeweed mitogen (PWM) was investigated. By using Percoll discontinuous density gradient centrifugation, peripheral blood nonphagocytic and nonadherent mononuclear cells were divided into low and high density fractions for which NK cells (Large granular lymphocytes, LGL) and T cells were enriched, respectively. These fractionated mononuclear cells were co-cultured with purified autologous B cells in the presence of PWM, and were examined for their helper and suppressor activities on differentiation of B cells to immunoglobulin-(IgM and IgG) producing cells by a highly sensitive reversed hemolytic plaque assay. The T cell-enriched high density fractions provided help for B cell differentiation to levels higher than that of unfractionated mononuclear cells. On the other hand, the NK-enriched low density fractions did not show helper activity, and when added to the culture of B cells plus helper T cells, they markedly suppressed B cell differentiation. This suppressive activity, as well as the NK cytotoxicity of the NK-enriched fractions, was abrogated by treatment of the cells with monoclonal antibody against human NK cells (HNK-1), but not against T cells (OKT3) in the presence of complement. NK cells also suppressed PWM-driven B cell differentiation in the presence of T4+ (helper/inducer T) but not T8+ (cytotoxic/suppressor T) cells; however, they showed no inhibition of soluble factor-induced B cell differentiation assayed in the absence of helper T cells. It is thus concluded that human peripheral blood NK cells exhibit an ability to suppress PWM-driven B cell differentiation, possibly by acting through the effect on helper T cells but not directly on B cells.     

Flavonoids: potent inhibitors of arachidonate 5-lipoxygenase

Various flavonoids were found to be relatively selective inhibitors of arachidonate 5-lipoxygenase which initiates the biosynthesis of leukotrienes with the activity of slow reacting substance of anaphylaxis. Cirsiliol (3',4',5-trihydroxy-6,7-dimethoxyflavone) was most potent, and the enzyme partially purified from rat basophilic leukemia cells was inhibited by 97% at a concentration of 10 microM (IC50, about 0.1 microM). 12-Lipoxygenases from bovine platelets and porcine leukocytes were also inhibited but at higher concentrations (IC50, about 1 microM), and fatty acid cyclooxygenase purified from bovine vesicular gland was scarcely affected. The compound at 10 microM suppressed by 99% the immunological release of slow reacting substance of anaphylaxis from passively sensitized guinea pig lung (IC50, about 0.4 microM).     

The ultrastructural basis of the permeability of arterial endothelium to horseradish peroxidase

The thoracic aorta and basilar artery, in which the incidence of atherosclerosis is known to be different, were examined to elucidate the correlation between the structure of the intercellular cleft junction between adjacent endothelial cells and its permeability to HRP. Tannic acid or HRP in the vessel lumen passed through the intercellular clefts of the thoracic aorta into the subendothelial space, whereas in the basilar artery they were unable to penetrate beyond the tight junction of the intercellular clefts. Freeze-fracture replicas revealed that the tight junctions of the thoracic aorta consisted of one to two junctional strands in most areas of the cleaved planes, with discontinuities in some places, whereas those of the basilar artery consisted of a continuous belt-like meshwork of six anastomosing junctional strands on average. These observations confirm that the structure of endothelial junctions in arteries has a close correlation with the permeability of the intercellular clefts to HRP.     

New In-vitro Test for IgE-mediated Hypersensitivity in Man

A new simple and sensitive in-vitro method for the diagnosis of type 1 (IgE-mediated) hypersensitivity in man is described. Sliced human skin is passively sensitized by reaginic serum from allergic patients and the presence of antigen-specific IgE on the sensitized slices is detected by assay of antigen-evoked histamine release. Serum from 12 out of 14 patients with clinical respiratory allergy and positive skin tests gave significant antigen-specific histamine release. This method, which is essentially an in-vitro model of the Prausnitz-Küstner reaction, should prove of value in the diagnosis of human reaginic hypersensitivity in man.     

Inactivation of T Antigen-Forming Capacities of Simian Virus 40 and Adenovirus 12 by Ultraviolet Irradiation

Methods to measure T antigen-forming capacities of simian virus 40 (SV40) and adenovirus 12 (Ad12) were investigated, and a method to measure the capacity in terms of T antigen-forming units was employed by the use of cytosine arabinoside. Plaque-forming units and T antigen-forming units of SV40, SV40 deoxyribonucleic acid, or Ad12 were inactivated by ultraviolet (UV) irradiation at the same rate, roughly following a single-hit curve. T-antigen formation by UV-irradiated SV40 and Ad12 was enhanced in cells multiply infected and in cells in a growing state. These observations showed that it was difficult or impossible to estimate the size of the gene for T antigen by UV inactivation.