Effects of prostaglandin E1 and indomethacin on fetal and neonatal lamb mesenteric artery responses to norepinephrine.

The effects of prostaglandin E1 (PGE1) and indomethacin on isolated fetal and neonatal lamb mesenteric artery responses to norepinephrine were investigated. PGE1 (1.5 micrometer) significantly reduced vasoconstriction responses to 0.5 to 5 micrometer norepinephrine. Indomethacin (1 micrometer) markedly potentiated the constrictor effects of 0.5 to 10 micrometer norepinephrine. PGE1 prevented the potentiating effect of indomethacin. Neither PGE1 nor indomethacin altered basal muscle tension. These results suggest that endogenous PGs modify adrenergic responses in the isolated mesenteric arteries of preterm and newborn lambs.     

Pyrophosphate-stimulated uptake of calcium into the germlings of Phytophthora infestans.

The uptake of 1 micrometer calcium into 6-h-old germination tubes of the fungus Phytophthora infestans follows Michaelis-Menten kinetics with a Km of 33 +/- 4 micrometer and a V of 0.3 nmol.min-1.(5 x 10(4) cells)-1.Uptake is inhibited by ruthenium red and lanthanum (both at 1 micrometer) and by the proton conductors 2,4-dinitrophenol (1 mM) and carbonylcyanide m-chlorophenylhydrazone and carbonylcyanide p-trifluoromethoxyphenylhydrazone (1--10 micrometer) and also by sodium azide. These data suggest that calcium uptake is dependent on energy and on a carrier. Calcium uptake is stimulated by pyrophosphate but not by ATP, orthophosphate, or polyphosphate. This stimulation is prevented by proton conductors or by incubation at 0 degrees C.     

Uptake and metabolism of adenosine by pig aortic endothelial and smooth-muscle cells in culture.

1. Adenosine, a potent vasodilator, is transported very efficiently by pig aortic endothelium in monolayer culture (approx. 50pmol/min per 10(6) cells at 2 micrometer). Uptake proceeds by diffusion at high (millimolar) substrate concentrations, and by two discrete transport processes (Km approx. 3 micrometer and 250 micrometer) at lower concentrations. Over 90% of the adenosine taken up at 10 micrometer or 100 micrometer is rapidly converted into adenine nucleotides (mainly ATP). 2. The high-affinity process is selectively inhibited by dipyridamole and by nitrobenzylthioinosine. Adenine preferentially inhibits the lower-affinity process, papapaverine inhibits both transport processes, and inosine has no significant effect. 3. Pig aortic smooth-muscle cells in culture show no high-affinity transport system for adenosine; uptake is much slower at low concentrations than that by endothelium (approx. 5pmol/min per 10(6) cells at 2 micrometer). Over 80% of the incorporated adenosine at 10 micrometer or 100 micrometer is rapidly converted into adenine nucleotides. 4. The uptake of adenosine by smooth-muscle cells is powerfully inhibited by adenine, but dipyridamole is much less potent than in endothelium. 5. We conclude that endothelial cells are mainly responsible for the removal of circulating adenosine.     

Life cycle of Isospora rivolta (Grassi, 1879) in cats and mice

The endogenous development of Isospora rivolta (Grassi) was studied in cats fed oocysts, and was compared with the endogenous cycle after feeding them mice infected with I. rivolta. For the mouse-induced cycle, 14 newborn cats were killed 12 to 240 h after having been fed mesenteric lymph nodes and spleens ofmice. Asexual and sexual development occurred throughout the small intestine, in epithelial cells of the villi and glands of Lieberkühn. The number of asexual generations was not determined with certainty, but there were at least 3 structurally different meronts. Type I meronts appeared at 12-48 h postinoculation (HPT). They were 8.5(6-13) x 5.1(3-6) micrometer, contained 2-8 merozoites, and divide by binary division or endodyogeny. Type II meronts were multinucleate merozoite-shaped meronts within a single parasitophorous vacuole. They were found at 48-172 HPI and measured 12.6(9-18) x 9.8(9-13) micrometer. Individual multinucleate merozoite-shaped meronts were 7-13 x 3-5 micrometer in sections and contained 2-30 slender (5.5 x 1.0 micrometer) merozoites. Type III meronts occurred at 72-192 HPI and gamonts at 72-96 HPI. Mature microgamonts measured 11.3(9-15) x 8.0(6-9) micrometer in sections and up to 21.5 x 14 micrometer in smears, and contained up to 70 microgametes. Macrogamonts measured 13.3(11-18) x 9.0(5-13) micrometer in sections and 18 x 16 micrometer in smears, and contained up to 70 microgametes. Macrogamonts measured 13.3(11-18) x 9.0(5-13) micrometer. Sporulation was completed within 24 h at 22-26 C. For the study of the oocyst-induced cycle in cats, 18 newborn cats were killed between 6 and 192 HPI. The endogenous development was essentially similar to the mouse-induced cycle, but merogony and gametogony occurred 12-48 h later than in the latter cycle. Isospora rivolta was pathogenic for newborn but not for weaned cats. Newborn cats fed 10(6) sporocysts or infected mice usually developed diarrhea 3-4 days after inoculation. Microscopically, desquamation of the tips of the villi and cryptitis were seen in the ilium and cecum in association with meronts and gamonts. For the study of the development of I. rivolta in mice, mice were killed from day 1 to 23 months after having been fed 10(5)-10(6) sporocysts, and their tissues were examined for the parasites microscopically, and by feeding to cats. The following conclusions were drawn. (A) Isospora rivolta most freqeuntly invaded the mesenteric lymph nodes ofmice and remained there for 23 months at least. Ii also invaded the spleen, liver, and skeletal muscles of mice. This species could not be passed from mouse to mouse. Sporozoites increased in size from approximately 6.8 x 4.9 micrometer on day 1 to approximately 13.4 x 6.9 micrometer on day 31 postinoculation. Division was not seen. Prepatent period was 4-7 days and patent periods ranged from 2 to several weeks.     

Regulation of pyruvate dehydrogenase activity in rat epididymal fat-pads and isolated adipocytes by adrenaline.

1. Dose-dependent effects of adrenaline on PDHa activity were investigated with both incubated rat epidiymal fat-pads and isolated adipocytes. 2. Adrenaline (10nM- 5 micrometer) decreased PDHa activity in fat-pads incubated with 5 mM-[U-14C]glucose + insulin (20 munits/ml). Changes in [U-14C]glucose incorporation into fatty acids in these tissues correlated only loosely with changes in PDHa activity. There was a good inverse relationship between adrenaline-induced changes in PDHa activity and increases in lipolysis (glycerol release). 3. Adrenaline (10nM - 0.5 micrometer) decreased PDHa activity in fat-pads incubated with 5 mM-[U-14C]pyruvate + insulin (20 munits/ml), whereas 1 micrometer- and 5 micrometer-adrenaline slightly increased PDHa activity. All concentrations of adrenaline tested decreased [U-14C]pyruvate incorporation into fatty acids. Between 10nM- and 0.5 micrometer-adrenaline percentage decreases in PDHa activity paralleled decreases in faty acid synthesis. 4. Effects of adrenaline on PDHa activity and fatty acid synthesis in fat-pads incubated with 5mM-[U-14C]pyruvate + insulin (20 munits/ml) could not be mimicked by addition of albumin-bound palmitate. 5. The response of PDHa activity to adrenaline (0.1 nM - 1 micrometer) in isolated adipocytes differed with the carbohydrate substrate used in the incubations. With 5 mM-glucose + insulin (20 munits/ml), PDHa activity was significantly increased by 10 nM-adrenaline, but not by 1 micrometer-adrenaline, the response to adrenaline being biphasic. There was some correlation between PDHa activity and accumulation of non-esterified fatty acids. With 5 mM-glucose alone adrenaline (0.1 nM - 1 micrometer) had no effect on PDHa activity even though lipolysis was increased by adrenaline (0.1 micrometer - 1 micrometer). With 5mM-fructose in the presence and absence of insulin, lipolytic doses of adrenaline decreased PDHa activity. No tested concentrations of adrenaline increased PDHa with this substrate. 6. In the presence of 5 mM-fructose, palmitate was significantly more effective than adrenaline with respect to the maximum decrease in PDHa activity that could be elicited. 4. The relationship of changes in PDHa activity to changes in lipogenesis and the likelihood of adrenaline-induced changes in PDHa activity being secondary to changes in non-esterified fatty acid metabolism are discussed.     

Characterization of a specific adenosine receptor on human lymphocytes.

We have examined the mechanism of action of adenosine, a naturally occurring nucleoside that has profound effects on lymphocyte function. Adenosine (0.01 micrometer to 10 micrometer) increased lymphocytes cAMP levels in a dose-dependent fashion with a maximal (10 micrometer) increase of about 4-fold, whereas adenine, guanosine, and inosine had no effect on lymphocyte cAMP levels at concentrations of 100 micrometer. Adenosine appears to act on the cell surface since 1) 2-chloroadenosine, a poorly metabolized adenosine analogue, was as active as adenosine and 2) dipyridamole, which markedly inhibited [3H]-adenosine uptake by human lymphocytes, did not affect adenosine-induced accumulation of cAMP. The specificity of the adenosine effect was established by showing that the methylxanthine derivatives, theophylline and 3-isobutyl-1-methylxanthine (IBMX), specifically block the accumulation of cAMP in lymphocytes induced by adenosine. Theophylline is a competitive inhibitor of the effect of adenosine, with an estimated dissociation constant of theophylline-receptor complex of about 6.3 X 10(-7) M. The results suggest that adenosine increases the intracellular cAMP content of lymphocytes as a result of its interaction with a specific membrane receptor which results in the activation of adenylate cyclase.     

CAMP-dissociation kinetics in hormone-dependent and -independent rat mammary tumor cytosols

Cytosols from 7, 12-dimethylbenz (alpha) anthracene-induced rat mammary tumors which exhibit different hormone-responsiveness were compared with respect to their cAMP-dissociation kinetics. At 22 degree C, pH 4.5, 1 micrometer cAMP, hormone-dependent mammary tumors exhibited monophasic dissociation rates with a rate constant of k-1 = 0.06 min-1. In contrast, hormone-independent mammary tumors exhibited biphasic dissociation curves with rate constants of k-1 = 0.47 and k-2 = 0.06 min-1. The binding of cAMP was completely reversible; radio-labeled ligand was completely dissociated by 1mM nonradioactive cAMP; the binding protein could be reassociated to its original binding level after dextran-coated charcoal adsorption. The mammary cytosols exhibited specific binding for cAMP which could be displaced partially by cGMP but not by ATP, ADP, AMP, or adenosine. Receptor inactivation during the course of incubation was negligible. Both mammary tissue cytosols exhibited similar association rates at 22 degree C, pH 4.5, 1 micrometer cAMP (k+1 = 5-7 x 10(5)M-1 min-1). These data indicate that mammary tissues exhibit 2 cAMP dissociation rates. Hormone-dependent mammary tumors exhibit a dissociation constant of a high affinity binding site (k-1/k+1 = 0.07 micrometer) whereas hormone-independent mammary tumors exhibit dissociation constants of one high affinity (k-1/k+1 = 0.07 micrometer) and a second low affinity site (k-1/k+1 = 0.05 micrometer).     

Expression and functional characterization of a Plasmodium falciparum Ca2+-ATPase (PfATP4) belonging to a subclass unique to apicomplexan organisms

We have obtained a full-length P type ATPase sequence (PfATP4) encoded by Plasmodium falciparum and expressed PfATP4 in Xenopus laevis oocytes to study its function. Comparison of the hitherto incomplete open reading frame with other Ca(2+)-ATPase sequences reveals that PfATP4 differs significantly from previously defined categories. The Ca(2+)-dependent ATPase activity of PfATP4 is stimulated by a much broader range of [Ca(2+)](free) (3.2-320 micrometer) than are an avian SERCA1 pump or rabbit SERCA 1a (maximal activity < 10 micrometer). The activity of PfATP4 is resistant to inhibition by ouabain (200 micrometer) or thapsigargin (0.8 micrometer) but is inhibited by vanadate (1 mM) or cyclopiazonic acid (1 microM). We used a quantitative polymerase chain reaction to assay expression of mRNA encoding PfATP4 relative to that for beta-tubulin in synchronized asexual stages and found variable expression throughout the life cycle with a maximal 5-fold increase in meronts compared with ring stages. This analysis suggests that PfATP4 defines a novel subclass of Ca(2+)-ATPases unique to apicomplexan organisms and therefore offers potential as a drug target.     

Effects of zinc chloride on the hydrolysis of cyclic GMP and cyclic AMP by the activator-dependent cyclic nucleotide phosphodiesterase from bovine heart.

In the presence of 10 micrometer Ca2+ and 5 mM Mg2+ (or 0.25 mM Mg2+), the addition of 100 micrometer Zn2+, Ni2+, Co2+, Fe2+, Cu2+ or 1 mM Mn2+ resulted in varying degrees of stimulation or inhibition of 10(-6) M cyclic GMP and cyclic AMP hydrolysis by the activator-dependent cyclic nucleotide phosphodiesterase from bovine heart in the absence or presence of phosphodiesterase activator. The substrate specificity of the enzyme was altered under several conditions. The addition of Zn2+ in the presence of 5 mM Mg2+ and the absence of activator resulted in the stimulation of cyclic GMP hydrolysis over a narrow substrate range while reducing the V 65% due to a shift in the kinetics from non-linear with Mg2+ alone to linear in the presence of Zn2+ and Mg2+. Zn2+ inhibited the hydrolysis of cyclic GMP and cyclic AMP in the presence of activator with Ki values of 70 and 100 micrometer, respectively. Zn2+ inhibition was non-competitive with substrate, activator and Ca2+ but was competitive with Mg2+. In the presence of 10 micrometer Ca2+ and activator, a Ki of 15 micrometer for Zn2+ vs. Mg2+ was noted in the hydrolysis of 10(-6) M cyclic GMP. Several effects of Zn2+ are discussed which have been noted in other studies and might be due in part to changes in cyclic nucleotide levels following phosphodiesterase inhibition.     

Diffusion of molecules on biological membranes of nonplanar form. A theoretical study.

Lateral mobility of molecules on cell membranes has been recently studied by fluorescence photobleaching recovery (FPR) techniques. The interpretation of these results in terms of diffusion along the membranes is based on the assumption that the surface is planar, although biological membranes may have blebs and microvilli. To study the effect of nonplanarity on the diffusion rate, the diffusion equation along curved surfaces was derived and was solved numerically for a "wavy" surface of the form A cos kx cos ky. Calculations show that for k = 10 pi micrometer-1 and a bleached spot of 1 micrometer in diameter, the time dependence of the intensity of fluorescence in the bleached spot depends on A at A less than 0.5 micrometer, while at higher values of A (a and 2 micrometer) the dependence is weak. If one calculates diffusion coefficients from FPR measurements and assumes that the membrane is planar, the resulting diffusion coefficient is not less than about half of the real one. Because of the tortuous shape of the spot boundary, increasing the microvilli length from 0.5 micrometer to 1 or 2 micrometer does not change the diffusion rates. These considerations are valid for times when the diffusion is dominated by molecules that were initially located close to the spot boundary.     

Rapid turnover of calcium in the endoplasmic reticulum during signaling. Studies with cameleon calcium indicators

HEK293 cells expressing the thyrotropin-releasing hormone (TRH) receptor were transfected with cameleon Ca(2+) indicators designed to measure the free Ca(2+) concentration in the cytoplasm, [Ca(2+)](cyt), and the endoplasmic reticulum (ER), [Ca(2+)](er). Basal [Ca(2+)](cyt) was about 50 nm; thyrotropin-releasing hormone (TRH) or other agonists increased [Ca(2+)](cyt) to 1 micrometer or higher. Basal [Ca(2+)](er) averaged 500 micrometer and fell to 50-100 micrometer over 10 min in the presence of thapsigargin. TRH consistently decreased [Ca(2+)](er) to 100 micrometer, independent of extracellular Ca(2+), whereas agonists for endogenous receptors generally caused a smaller decline. When added with thapsigargin, all agonists rapidly decreased [Ca(2+)](er) to 5-10 micrometer, indicating that there is substantial store refilling during signaling. TRH increased [Ca(2+)](cyt) and decreased [Ca(2+)](er) if applied after other agonists, whereas other agonists did not alter [Ca(2+)](cyt) or [Ca(2+)](er) if added after TRH. When Ca(2+) was added back to cells that had been incubated with TRH in Ca(2+)-free medium, [Ca(2+)](cyt) and [Ca(2+)](er) increased rapidly. The increase in [Ca(2+)](er) was only partially blocked by thapsigargin but was completely blocked if cells were loaded with 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. In conclusion, these new Ca(2+) indicators showed that basal [Ca(2+)](er) is approximately 500 micrometer, that [Ca(2+)](er) has to be >100 micrometer to support an increase in [Ca(2+)](cyt) by agonists, and that during signaling, intracellular Ca(2+) stores are continuously refilled with cytoplasmic Ca(2+) by the sarcoendoplasmic reticulum Ca(2+)-ATPase pump.     

Purification and characterization of two tRNA-(guanine)-methyltransferases from rat liver

tRNA(guanine-1-)-methyltransferase (EC 2.1.1.31) and tRNA(N2-guanine)-methyltransferase I (EC 2.1.1.32) were isolated from rat liver. The (guanine-1-)-methyltransferase preparation is 6800-fold purified and is free from contaminating methyltransferases or ribonuclease. The molecular weight of (guanine-1-)-methyltransferase is 83 000. Of seven purified Escherichia coli tRNAs examined, only tRNAMetf was utilized as substrate by (guanine-1-)-methyltransferase. The methylation of tRNAMetf is maximally stimulated by 40 mM putrescine with a pH optimum of 8.0. Using E. coli K-12 tRNA, the Km for S-adenosylmethionine is 3 micrometer and Ki for S-adenosylhomocysteine is 0.11 micrometer for (guanine-1-)-methyltransferase. (N2-Guanine-)-methyltransferase is 6200-fold purified and is also free of interfering enzymes. It has a molecular weight of 69 000. E. coli tRNAPhe, tRNAVal and tRNAArg are substrates for this enzyme which introduces a methyl at the 2-amino group of the guanine at position 10 from the 5'-terminus of these tRNAs. The methylation of tRNAPhe is maximally stimulated by 100 micrometer spermidine with a pH optimum of 8.0. (N2-Guanine-)-methyltransferase has a Km for S-adenosylmethionine of 2 micrometer and a Ki for S-adenosylhomocysteine of 23 micrometer with E. coli K-12 tRNA as methyl acceptor.     

Activation of potassium and chloride channels by tumor necrosis factor alpha. Role in liver cell death

Despite abundant evidence for changes in mitochondrial membrane permeability in tumor necrosis factor (TNF)-mediated cell death, the role of plasma membrane ion channels in this process remains unclear. These studies examine the influence of TNF on ion channel opening and death in a model rat liver cell line (HTC). TNF (25 ng/ml) elicited a 2- and 5-fold increase in K(+) and Cl(-) currents, respectively, in HTC cells. These increases occurred within 5-10 min after TNF exposure and were inhibited either by K(+) or Cl(-) substitution or by K(+) channel blockers (Ba(2+), quinine, 0.1 mm each) or Cl(-) channel blockers (10 microm 5-nitro-2-(3-phenylpropylamino)benzoic acid and 0.1 mm N-phenylanthranilic acid), respectively. TNF-mediated increases in K(+) and Cl(-) currents were each inhibited by intracellular Ca(2+) chelation (5 mm EGTA), ATP depletion (4 units/ml apyrase), and the protein kinase C (PKC) inhibitors chelerythrine (10 micrometer) or PKC 19-36 peptide (1 micrometer). In contrast, currents were not attenuated by the calmodulin kinase II 281-309 peptide (10 micrometer), an inhibitor of calmodulin kinase II. In the presence of actinomycin D (1 micrometer), each of the above ion channel blockers significantly delayed the progression to TNF-mediated cell death. Collectively, these data suggest that activation of K(+) and Cl(-) channels is an early response to TNF signaling and that channel opening is Ca(2+)- and PKC-dependent. Our findings further suggest that K(+) and Cl(-) channels participate in pathways leading to TNF-mediated cell death and thus represent potential therapeutic targets to attenuate liver injury from TNF.     

Acute cadmium exposure inactivates thioltransferase (Glutaredoxin), inhibits intracellular reduction of protein-glutathionyl-mixed disulfides, and initiates apoptosis

Oxidative stress broadly impacts cells, initiating regulatory pathways as well as apoptosis and necrosis. A key molecular event is protein S-glutathionylation, and thioltransferase (glutaredoxin) is a specific and efficient catalyst of protein-SSG reduction. In this study 30-min exposure of H9 and Jurkat cells to cadmium inhibited intracellular protein-SSG reduction, and this correlated with inhibition of the thioltransferase system, consistent with thioltransferase being the primary intracellular catalyst of deglutathionylation. The thioredoxin system contributed very little to total deglutathionylase activity. Thioltransferase and GSSG reductase in situ displayed similar dose-response curves (50% inhibition near 10 micrometer cadmium in extracellular buffer). Acute cadmium exposure also initiated apoptosis, with H9 cells being more sensitive than Jurkat. Moreover, transfection with antisense thioltransferase cDNA was incompatible with cell survival. Collectively, these data suggest that thioltransferase has a vital role in sulfhydryl homeostasis and cell survival. In separate experiments, cadmium inhibited the isolated component enzymes of the thioltransferase and thioredoxin systems, consistent with the vicinal dithiol nature of their active sites: thioltransferase (IC(50) approximately 1 micrometer), GSSG reductase (IC(50) approximately 1 micrometer), thioredoxin (IC(50) approximately 8 micrometer), thioredoxin reductase (IC(50) approximately 0.2 micrometer). Disruption of the vicinal dithiol on thioltransferase (via oxidation to C22-SS-C25; or C25S mutation) protected against cadmium, consistent with a dithiol chelation mechanism of inactivation.     

Photoaffinity inhibition of dipeptide transport in Escherichia coli.

A dipeptide containing a nitrene precursor, glycyl-4-azido-2-nitro-L-phenylalanine, has been synthesized. This compound is a photoaffinity inhibitor of dipeptide transport in E. coli. In the dark, the dipeptide is a reversible inhibitor of glycylglycine uptake by live E. coli W cells. The 14C-labeled compound is a substrate for the transport system, with a Km of 7 micrometer and V max of 5 x 10(3) molecules cell-1 s-1 (compare 9 micrometer and 1 x 10(4) molecules cell-1 s-1, respectively, for the transport of glycylglycine under the same conditions). When intact E. coli cells are photolyzed at approximately 350 nm in the presence of the photolabile dipeptide, their ability to transport either glycylglycine or unphotolyzed glycyl-4-azido-2-nitro-L-phenylalanine is irreversibly inhibited, but their ability to transport arginine is unaffected. The presence of glycylglycine in the medium during photolysis protects the cells against the light-dependent inactivation of dipeptide transport.     

Micelle and acid-soap formation of linoleic acid and 13-L-hydroperoxylinoleic acid being substrates of lipoxygenase-1.

Surface tension measurements of linoleic acid solutions in 0.1 M sodiumborate buffer pH 10 at 23 degrees C showed that at increasing the linoleic acid concentration a sharp transition from monomers to micelles occurs at 167 micrometer. At pH 9 and 8 formation of acid-soap dimers from monomers starts at 60 micrometer and 21 micrometer respectively. The concentration range at which only monomers exist is therefore markedly reduced. For 13-L-hydroperoxylinoleic acid at pH 10 acid-soap formation still takes place, starting at approx. 220 micrometer. The total lipid concentration at which acid-soap or micelle formation starts in mixtures of linoleic acid and 13-L-hydroperoxylinoleic acid has been determined in relation to the molar ratio of both acids.     

Thrombin-mediated feedback activation of factor XI on the activated platelet surface is preferred over contact activation by factor XIIa or factor XIa

To study the pathways for initiation of intrinsic blood coagulation, activated human platelets were compared with dextran sulfate as surfaces for factor XI activation by factor XIIa, factor XIa, or thrombin. Activated gel-filtered platelets promoted the activation of factor XI (60 nm) by thrombin (0.02-10 nm, EC(50) approximately 100 pm, threshold concentration approximately 10 pm) at initial rates 2- to 3-fold greater than those obtained with dextran sulfate in the presence of either high molecular weight kininogen (45 nm) and ZnCl(2) (25 micrometer) or prothrombin (1.2 micrometer) and CaCl(2) (2 mm). The maximum rates of factor XI activation achieved in the presence of activated gel-filtered platelets were 30 nm.min(-1) with thrombin, 6 nm.min(-1) with factor XIIa and 2 nm.min(-1) with factor XIa. Values of turnover number calculated at various enzyme concentrations (0.05-1 nm) were 24-167 (mean = 86) min(-1) for thrombin, 4.6-50 (mean = 21) min(-1) for factor XIIa, and 1.3-14 (mean = 8) min(-1) for factor XIa. A physiological concentration of fibrinogen (9.0 micrometer) inhibited factor XI activation by thrombin (but not by factor XIIa) in the presence of dextran sulfate but not in the presence of gel-filtered platelets. Compared with factors XIIa and XIa, thrombin is the preferred factor XI activator, and activated platelets are a relevant physiological surface for thrombin-mediated initiation of intrinsic coagulation in vivo.     

Interindividual variation in the responses of cultured human lymphocytes to exposure from DNA damaging chemical agents: interindividual variation to carcinogen exposure.

Human population variability to standardized doses of N-acetoxy-2-acetylaminofluorene (NA-AAF) and 7, 12-dimethylbenz(a) anthracene (DMBA) was determined in cultured lymphocytes by measuring (a) differential stimulation of unscheduled DNA synthesis after 1 h induction of DNA damage by 10 micrometer NA-AAF, (b) the level of NA-AAF induced chromosome aberrations remaining after 8 h of DNA-repair synthesis, and (c) the level of [3H]DMBA bound to DNA after 18 h incubation of resting lymphocytes in 5 micrometer DMBA. All 3 parameters indicated individual variation to carcinogen exposure and were correlated to the population differences in age, sex, blood pressure and mortality rates. Males always had a greater potential to accumulate DNA-damage than did females regardless of the sampled population. DNA-damage potentials increased with increasing age, blood pressure or mortality rates. There was always proportionally greater DNA-damage potentials in the males than in females. The in vitro response of mature granulocytes to a 10 micrometer NA-AAF dose, as estimated by [3H] thymidine incorporation from unscheduled DNA synthesis, was much lower than lymphocyte response. Nevertheless, individual variations in granulocyte NA-AAF induced unscheduled DNA synthesis paralleled the inter-individual fluctuations observed in the lymphocyte responses to NA-AAF.     

CaV2.2 and CaV2.3 (N- and R-type) Ca2+ channels in depolarization-evoked entry of Ca2+ into mouse sperm

As sperm prepare for fertilization, surface Ca(2+) channels must open to initiate required, Ca(2+)-mediated events. However, the molecular identity and functional properties of sperm Ca(2+) channels remain uncertain. Here, we use rapid local perfusion and single-cell photometry to examine the kinetics of calcium responses of mouse sperm to depolarizing stimuli. The linear rise of intracellular [Ca(2+)] evoked by approximately 10-s applications of an alkaline high [K(+)] medium directly reports activity of voltage-gated Ca(2+) channels. Little response occurs if external Ca(2+) is removed or if external or internal pH is elevated without depolarization. Responses are inhibited 30-40% by 30-100 micrometer Ni(2+) and more completely by 100-300 micrometer Cd(2+). They resist the dihydropyridines nitrendipine and PN200-110, but 1-10 micrometer mibefradil inhibits reversibly. They also resist the venom toxins calciseptine, omega-conotoxin MVIIC, and kurtoxin, but omega-conotoxin GVIA (5 micrometer) inhibits approximately 50%. GVIA also partially blocks transient, low voltage activated Ca(2+) currents of patch-clamped spermatids. Differential sensitivity of sperm responses to Ni(2+) and Cd(2+) and partial blockade by GVIA indicate that depolarization opens at least two types of voltage-gated Ca(2+) channels in epididymal sperm examined prior to capacitation. Involvement of a previously undetected Ca(V)2.2 (N-type) channel, suggested by the action of GVIA, is substantiated by immunodetection of Ca(2+) channel alpha(1B) subunits in sperm and sperm extracts. Resistance to dihydropyridines, calciseptine, MVIIC, and kurtoxin indicates that Ca(V)1, Ca(V)2.1, and Ca(V)3 (L-, P/Q-, and T-type) channels contribute little to this evoked response. Partial sensitivity to 1 micrometer mibefradil and an enhanced sensitivity of the GVIA-resistant component of response to Ni(2+) suggest participation of a Ca(V)2.3 (R-type) channel specified by previously found alpha(1E) subunits. Our examination of depolarization-evoked Ca(2+) entry indicates that mature sperm possess a larger palette of voltage-gated Ca(2+) channels than previously thought. Such diversity may permit specific responses to multiple cues encountered on the path to fertilization.     

Roles of insulin receptor substrate-1, phosphatidylinositol 3-kinase, and release of intracellular Ca2+ stores in insulin-stimulated insulin secretion in beta -cells

The signaling pathway by which insulin stimulates insulin secretion and increases in intracellular free Ca(2+) concentration ([Ca(2+)](i)) in isolated mouse pancreatic beta-cells and clonal beta-cells was investigated. Application of insulin to single beta-cells resulted in increases in [Ca(2+)](i) that were of lower magnitude, slower onset, and longer lifetime than that observed with stimulation with tolbutamide. Furthermore, the increases in [Ca(2+)](i) originated from interior regions of the cell rather than from the plasma membrane as with depolarizing stimuli. The insulin-induced [Ca(2+)](i) changes and insulin secretion at single beta-cells were abolished by treatment with 100 nm wortmannin or 1 micrometer thapsigargin; however, they were unaffected by 10 micrometer U73122, 20 micrometer nifedipine, or removal of Ca(2+) from the medium. Insulin-stimulated insulin secretion was also abolished by treatment with 2 micrometer bisindolylmaleimide I, but [Ca(2+)](i) changes were unaffected. In an insulin receptor substrate-1 gene disrupted beta-cell tumor line, insulin did not evoke either [Ca(2+)](i) changes or insulin secretion. The data suggest that autocrine-activated increases in [Ca(2+)](i) are due to release of intracellular Ca(2+) stores, especially the endoplasmic reticulum, mediated by insulin receptor substrate-1 and phosphatidylinositol 3-kinase. Autocrine activation of insulin secretion is mediated by the increase in [Ca(2+)](i) and activation of protein kinase C.