Density-dependent recognition of cell surface GM3 by a certain anti-melanoma antibody, and GM3 lactone as a possible immunogen: requirements for tumor-associated antigen and immunogen

A mouse monoclonal antibody M2590, previously established after immunization of mice (C57BL/6) with syngeneic melanoma B16 cells and showing preferential reactivity with various types of melanoma over other tumor and normal cells or tissues, was shown to be directed to GM3 ganglioside. Since GM3 is widely distributed in essentially all types of animal cells, there is a conflict with the concept of a tumor-associated antigen and immunogen. Studies on the reactivity of M2590 antibody with various cells having different GM3 density at their cell surface, including cells treated with sialidase, liposomes, and solid-phase lipid layer containing different GM3 concentrations, have indicated that 1) reactivity of the antibody M2590 depends greatly on the density of GM3 exposed at the cell surface, on liposomes, or on solid phase; and 2) there is a threshold density that is recognized by the antibody in all-or-none fashion. In addition, the antibody M2590 reacts not only with GM3 but also with GM3 lactone, and the binding affinity of the antibody to GM3 lactone is strikingly higher than to GM3; however, the antibody does not react with GM3 ethyl ester. GM3 lactone was detected in melanoma as 3H-labeled GM3 gangliosidol after melanoma cells were directly treated with NaB[3H]4. A comparative immunization of BALB/c mice with GM3 and GM3 lactone showed that GM3 lactone is a much stronger immunogen than GM3, although the antibody elicited reacts with both GM3 and its lactone. Thus, the real immunogen could be GM3 lactone, although it is a minor membrane component.

Susceptibility of diabetic rat aorta to self-deactivation during prostacyclin synthesis

The ability of aortic rings to produce PGI2 markedly decreased in streptozotocin-induced diabetic rats when compared with age-matched controls. Arachidonic acid dose-dependently stimulated the production of PGI2 both in normal and diabetic rat aorta during 5 min incubation. The deficiency in PGI2 production in diabetic rat aorta was temporarily corrected by the addition of 5-20 microM of arachidonic acid. However, when aortic rings were incubated over a period of 10 min in the presence of arachidonic acid, the ability of PGI2 production in diabetic rats markedly decreased. Repeated exposures of aortic rings to arachidonic acid also markedly reduced PGI2 production in diabetic rats. PGI2 production in diabetic rat aorta was inactivated more readily than in normal rat aorta by pre-incubation with t-butyl hydroperoxide. Phenol had a protective effect on incubation-induced inactivation of PGI2 generating activity in diabetic rat aorta. Serum markedly stimulated PGI2 synthesis in normal and diabetic rat aorta. The serum activity in diabetic rats was less potent than in normal rats. Melittin and dipyridamole were effective in stimulating PGI2 release from diabetic rat aorta. These results suggest that enzymes in the aorta involved in PGI2 synthesis from released arachidonic acid are susceptible to self-inactivation in diabetic rats during the metabolism of arachidonic acid. This may contribute to the defect of PGI2 synthesis in diabetic rat aorta in addition to the decreased availability of the substrate.

Enhancement of stimulation-evoked catecholamine release from cultured bovine adrenal chromaffin cells by forskolin

Acetylcholine (ACh) increased cyclic AMP levels in cultured bovine chromaffin cells with a peak effect at 1 min after the addition. Pretreatment with forskolin (0.3 microM) enhanced the ACh-evoked cyclic AMP increase. The catecholamine (CA) release induced by ACh was enhanced by forskolin, but forskolin alone did not enhance the CA release. The effect of forskolin increased dose-dependently up to 1 microM, but decreased at higher concentrations. Dibutyryl cyclic AMP (DBcAMP) also enhanced ACh-evoked CA release, but the effect was less potent than that of forskolin. Forskolin enhanced both [3H]norepinephrine ([3H]NE) and endogenous CA release evoked by 30 mM K+ from cells that were preloaded with [3H]NE. The effects of forskolin were substantial when CA release was evoked with low concentrations of ACh or excess K+, but decreased with higher concentrations of the stimulants. Forskolin also enhanced the CA release induced by ionomycin and veratrine, or by caffeine in Ca2+-free medium. The potentiation by forskolin of the ACh-evoked CA release was manifest in low Ca2+ concentrations in the medium, but decreased when Ca2+ concentration was increased. These results suggest that cyclic AMP may play a role in the modulation of CA release from chromaffin cells.

Stimulation-evoked Ca2+ fluxes in cultured bovine adrenal chromaffin cells are enhanced by forskolin

Forskolin, 1 microM, increased acetylcholine (ACh)-stimulated 45Ca uptake by chromaffin cells. The stimulatory effects of forskolin decreased with increasing concentration of ACh. The attenuation of the effect of forskolin on 45Ca uptake as a function of ACh concentration correlated well with changes in the forskolin effect on ACh-evoked catecholamine (CA) release. Forskolin increased excess KCl- and veratrine-evoked CA release and 45Ca uptake. Forskolin by itself stimulated 45Ca efflux and enhanced ACh-, excess KCl-, and veratrine-stimulated 45Ca efflux. High doses of forskolin inhibited both ACh-evoked 45Ca uptake and CA release. The inhibitory action of forskolin was specific to receptor-mediated response because excess KCl- and veratrine-stimulated 45Ca uptake and CA release were not inhibited. Forskolin, 0.3-30 microM, dose-dependently increased caffeine-stimulated CA release and 45Ca efflux in the absence of Ca2+ in the medium, and the effects were mimicked by dibutyryl cyclic AMP. These results suggest that cyclic AMP increases stimulation-induced CA release by enhancing calcium uptake across the plasma membrane and/or altering calcium flux in an intracellular calcium store.

Increase in catecholamine release and 45Ca2+ uptake induced by GABA in cultured bovine adrenal chromaffin cells

The role of Ca2+ in GABA-evoked catecholamine (CA) release from adrenal medulla was investigated in primary cultures of bovine adrenal chromaffin cells. GABA facilitated the 45Ca2+ uptake associated with the increase of Ca release in cultured bovine adrenal chromaffin cells. The effects of GABA on both 45Ca2+ uptake and CA release were blocked by bicuculline and picrotoxin. Nifedipine reduced the 45Ca2+ uptake and CA release induced by GABA. These data support our previous suggestion that the activation of GABA receptors on adrenal chromaffin cells facilitates the Ca2+ influx through voltage-sensitive Ca2+ channels, leading to the release of CA.

An unusual complication of a myocardial electrode--apatite mantle on the platinum-iridium spurs

A case of a high excitation threshold that occurred 2 years 5 months after the initial implantation of pacemaker electrodes is described in a girl 4 years 3 months of age. This complication was considered to be due to calcification of the platinum-iridium electrode spurs. The calcified material was shown to be a kind of apatite using the X-ray powder diffraction method. This complication is rare, but it must be kept in mind since battery longevity has markedly improved in recent years.

Forskolin enhancement of acetylcholine-evoked cyclic AMP formation and catecholamine release in perfused dog adrenals

Unstimulated efflux of cyclic AMP from perfused dog adrenal glands was not altered by 0.1 microM of forskolin and was slightly increased by 0.3 and 1.0 microM of forskolin. ACh stimulated efflux of cyclic AMP which preceded CA release and the efflux was dose-dependently enhanced by forskolin. Forskolin did not affect the spontaneous CA release but enhanced ACh-evoked catecholamine (CA) release. There was a close correlation between the dose relationship of forskolin enhancement of stimulated-cyclic AMP efflux and that of evoked-CA release. ACh-evoked CA release in the presence of forskolin was further potentiated by R020-1724, a phosphodiesterase inhibitor. CA release evoked by excess K+, or by caffeine in the presence or absence of external Ca2+ was also potentiated by forskolin. These results suggests that cyclic AMP generation may increase in response to stimulation of adrenal chromaffin cells and that the resulting increase of the nucleotide may function as a facilitating modulator of CA release.

Stimulation-evoked cyclic nucleotides efflux from isolated perfused dog adrenals and possible involvement of calcium

Nicotine and muscarine caused the transient increase in cAMP and cGMP efflux from dog adrenal glands followed by a small but lasting increase in the nucleotide efflux. The initial increase preceded catecholamine (CA) release and the latter slowly developed. Nicotine and muscarine caused the maximal increase of cAMP and cGMP levels in adrenal medulla 15 sec after the treatment, and these effects were antagonized by hexamethonium and atropine, respectively. Hexamethonium in combination with atropine, verapamil and an omission of Ca2+ in the medium prevented ACh from producing the increase in cyclic nucleotide efflux and CA release. Reintroduction of Ca2+ (1.3 mM) in fluid after perfusion with Ca2+ and Mg2+-free fluid caused the transient increase in cyclic nucleotide efflux and CA release. Adenylate cyclase activity in adrenal medulla was activated by Ca2+. These results may suggest that cAMP formation was increased by activation of adenylate cyclase as a result of increased influx of Ca2+ when adrenal medulla were stimulated.

Facilitation of acetylcholine-evoked catecholamine release by cyclic AMP on isolated perfused dog adrenal glands

The effects of cyclic nucleotides on catecholamine (CA) release and Ca2+ efflux were determined on isolated dog adrenals perfused with 1.3 mM Ca2+ containing fluid except indicated. Dibutyryl cyclic AMP (DBcAMP, 50 microM--1 mM) substantially enhanced CA release evoked by acetylcholine (ACh) and slightly increased the spontaneous CA release. Dibutyryl cyclic GMP (100-500 microM) narrowly increased the basal CA release. DBcAMP, 200 microM also significantly facilitated CA release caused by nicotine, bethanechol and excess K+, and by caffeine in the absence of extracellular Ca2+. 45Ca efflux evoked by ACh and by caffeine in the absence of extracellular Ca2+ from prelabelled adrenals with 45Ca was enhanced significantly by DBcAMP, 200 microM. These results suggest that cAMP may function as a facilitatory modulator in CA release from the adrenal medulla via in part the effect on Ca2+ flux including alterations in the function of systems for intracellular Ca2+ homeostasis.

Membrane plasma separation through small-area, hollow-fiber filters

The filtration capabilities of small polypropylene hollow-fiber plasma filters with membrane areas ranging from 100 to 1,000 cm2 have been investigated. It is found that the filtration flux per unit membrane area is approximately proportional to the wall shear rate gamma w at least up to gamma w = 7,500 s-1. As a result, the total filtration flow rate increases very little when the number of fibers is increased as the increase in membrane area is offset by the decrease in shear rate, but it increases with the fiber length L as L 2/3. Hemolysis occurs when the transmembrane pressure exceeds a certain threshold, but this threshold is itself an increasing function of shear rate. As a result, it is possible to circulate high blood flow rates even in very small filters (100 cm2) without hemolysis, provided the fiber length is below a critical value.

Potassium ion is indispensable to the catecholamine releasing response of dog adrenals to gamma-aminobutyric acid

The effect of potassium ion on the GABA-evoked catecholamine (CA) release from isolated perfused adrenal glands of the dog was investigated. When omitting the external potassium ion, the basal release of CA was increased. During this period GABA no longer caused the increase in CA release and moreover the increased basal release was diminished reversibly by GABA. 3-Amino-1-propane-sulfonic acid, a GABAA agonist, mimicked the action of GABA in K+-free solution, while baclofen, a GABAB agonist, did not cause CA release in normal solution and did not alter the basal release in K+-free solution. The inhibition by GABA of the basal CA release in K+-free solution was blocked by bicuculline. The potency of the CA releasing action of GABA was dependent on the concentration of external K+ between 1-10 mM. Reintroduction of K+ to glands which had been perfused with K+-free solution immediately reduced the basal release of CA whereas it recovered the CA releasing action of GABA. These results suggest that GABA-evoked CA release is dependent on potassium ion. The possible mechanisms by which GABA evoked CA release are discussed.

The nature of the stimulatory action of gamma-aminobutyric acid in the isolated perfused dog adrenals

The effect of gamma-aminobutyric acid (GABA) on catecholamine (CA) release from adrenal medulla was investigated. GABA and GABA agonists, 3-amino-1-propane-sulfonic acid and imidazole-4-acetic acid caused CA release from isolated perfused dog adrenals in a dose-dependent manner, and no tachyphylaxis to GABA was observed. CA release elicited by GABA was antagonized by bicuculline and picrotoxin. This antagonism was specific for GABA- and GABA agonist-induced responses, response to acetylcholine being unaffected. Pretreatment with atropine plus hexamethonium did not affect the response to GABA. GABA-induced CA release was abolished by the removal of Ca2+ from perfusion medium, but not by the removal of Na+ or Cl-. Verapamil, CoCl2 and dibucaine blocked the effect of GABA. A Na+ channel blocker, tetrodotoxin did not reduce GABA-evoked CA release. These results suggest that GABA may interact with its receptor to evoke CA release from adrenal medulla in a fashion of Ca2+-dependence and independence on external Na+ or Cl-.

Effect of sodium azide on catecholamine release from isolated adrenal gland and on guanylate cyclase

Sodium azide and other compounds which activate guanylate cyclase could stimulate catecholamine (CA) release from perfused dog adrenals. Verapamil reduced the secretory effect of sodium azide, but atropine and hexamethonium did not affect it while isobutyl methylxanthine potentiated it. Ca2+ deprivation abolished the stimulating effect of sodium azide on CA release and cyclic AMP output but the increased output of cyclic GMP remained. These results suggest the involvement of the Ca2+ influx mechanism in the secretory action of sodium azide.

Inhibition of gamma-aminobutyric acid release from synaptosomes by local anesthetics

The effects of local anesthetics on the synthesis, release, and degradation of gamma-aminobutyric acid (GABA) in rat brains were investigated. The addition of procaine, lidocaine, cocaine, or tetracaine did not alter either glutamic acid decarboxylase (GAD) activity or GABA transaminase (GABA-T) activity in vitro. Neither did the enzyme activities in rats with local anesthetic-induced convulsions differ from control values. Tetracaine inhibited high K+-evoked [2,3-3H]GABA release from synaptosomes of rat brain in a dose-dependent manner with a minimal effective concentration of 10(-4) M. Cocaine, lidocaine, and procaine also reduced the release, although they were less potent than tetracaine. The GABA release inhibitors in order of potency are tetracaine, cocaine, lidocaine, and procaine which correlates well with their relative toxicity as convulsants. These results suggest that local anesthetics reduce GABAergic activities by inhibiting the release of the neurotransmitter from the nerve terminals, and that inhibition of the GABA system may be involved in the mechanism of local anesthetic-induced convulsions.

Labelled-calcium release from rat mandibles exposed to prostaglandins in vitro

Bone resorptive effects of prostaglandins (PGs) in cultured mandibular bone tissue of rat fetus prelabelled with 45Ca were examined in comparison with those in radius-ulna. PGE1 (3 X 10(-6)-10(-4) M) and PGE2 (3 X 10(-8)-10(-4) M) could significantly stimulate the release of 45Ca from mandible with a peak effect at 3 X 10(-6) M. The effects of PGEs were more marked in mandible than in radius-ulna. Salmon calcitonin (SCT) inhibited the stimulating effect of PGE2. PGF 2 alpha did not cause the significant increase of 45Ca-release. Parathyroid hormone (PTH) at concentrations of 0.01-1.0 IU/ml dose-dependently stimulated 45Ca-release and the effects were greater in mandible than in radius-ulna. Dibutyryl cyclic (DBc)-AMP stimulated the release of 45Ca in mandible with a sharp peak effect at 5 X 10(-4) M. The results indicate that mandible is more susceptible to these bone resorptive agents than radius-ulna.

Protection from local anesthetic-induced convulsions by gamma-aminobutyric acid

The effects of gamma-aminobutyric acid (GABA) on the induction of convulsions by local anesthetics were investigated in mice and rats. Intraventricular administration of 0.8-1.6 mg GABA protected rats against convulsions induced by procaine, lidocaine, cocaine, and tetracaine in a dose-related manner. Intraperitoneal gamma-acetylenic GABA was also effective against procaine-induced convulsions in mice, but the metabolites of GABA, gamma-hydroxybutyrate, and gamma-butyrolactone were without effect. Intraventricular GABA, 1.6 mg, delayed the onset of convulsions induced by hydrazine, but had no influence on the incidence of convulsions induced by nicotine, pentylenetetrazol, picrotoxin, or strychnine. These results suggest that the GABA system may be involved in the mechanisms of local anesthetic-induced convulsions.

Effects of pyruvate and other metabolites on cyclic GMP levels in incubations of rat hepatocytes and kidney cortex

Pyruvate increased cyclic GMP levels in rat hepatocytes. The effects were observed without or with 1-methyl-3-isobutylxanthine. Lactate, acetate, oxaloacetate, alpha-ketoglutarate, succinate, acetoacetate and beta-hydroxybutyrate also increased cyclic GMP levels. Some compounds increased cyclic GMP in kidney cortex slices. The effects were dependent upon Ca2+ in the medium. Cyclic AMP was increased 30-50% by some of these substances with 2.6 mM Ca2+. Rotenone, oligomycin, antimycin, dinitrophenol, KCN, and arsenate decreased GTP and ATP, basal cyclic GMP and the pyruvate effect, but did not alter cyclic AMP. Although fluoroacetate alone had no effect on cyclic nucleotides, GTP, or ATP, it potentiated the pyruvate effect on cyclic GMP. Adenosine and guanosine increased cyclic GMP and GTP to a similar extent of 30-50%. Aminooxyacetate, cycloserine, pentenoic acid and mepacrine decreased the pyruvate effect while cycloserine or mepacrine alone increased cyclic GMP. Citrate and mepacrine inhibited soluble and particulate guanylate cyclase from rat liver while cycloserine and acetoacetate increased guanylate cyclase activity. None of the other compounds altered guanylate cyclase activity. These results indicate that various metabolites and inhibitors can alter cyclic GMP accumulation in hepatocytes and renal cortex slices. Several mechanisms may be involved in these effects.

Possible mechanisms of sustained tremor induction by nicotine in pilocarpine treated animals

Alterations of steady state and metabolism of putative neurotransmitters were studied in the brain of rats with a sustained tremor evoked by nicotine and pilocarpine. The norepinephrine content in several brain regions was decreased whereas striatal dopamine was unchanged. Homovanillic acid concentrations were slightly increased, while 5-hydroxyindoleacetic acid concentrations were markedly increased. Pilocarpine alone increased the 5-hydroxytryptamine (5-HT) turnover rate at high ambient temperature (30-32 degrees C), but not at normal ambient temperature (22 +/- 2 degrees C), atropine partially blocked the increase of 5-HT turnover rate by pilocarpine. Pretreatment with p-chlorophenylalanine and hemicholinium-3 decreased the tremor intensity elicited by nicotine and pilocarpine . It is proposed that the increase of cholinergic function caused by nicotine and the activation of muscarinic receptors and the increase in 5-HT function caused by pilocarpine might be involved in the mechanisms of tremor induction by nicotine and pilocarpine.