First report of anthelmintic resistance in gastrointestinal nematodes of sheep from costa rica

As the prevalence and severity of anthelmintic resistance continue to rise, nematode infections in sheep correspondingly reduce the profitability of the sheep industry. In Costa Rica, sheep production systems are increasing in both number and importance. A field trial study was carried out to detect the level of anthelmintic resistance to albendazole and ivermectin in gastrointestinal nematodes (GIN) of sheep from seven farms in Costa Rica. Resistance was determined using the fecal egg count reduction test (FECRT). Three treatment groups were assessed on each farm: control, albendazole, and ivermectin. Haemonchus spp. (71%), Strongyloides sp. (57%), and Trichostrongylus spp. (43%) presented resistance levels to albendazole, whereas Strongyloides sp. (43%), Haemonchus spp. (29%), and Trichostrongylus spp. (29%) were resistant to ivermectin. Haemonchus spp., Strongyloides sp., and Trichostrongylus spp. were the most resistant GIN to both products. This study suggests that frequency of treatment, exclusive chemical control, and visual estimation of animal weight to calculate dosage may contribute to the high levels of anthelmintic resistance that were observed on the farms analyzed herein.

Brefeldin A block of integrin-dependent mechanosensitive ATP release from Xenopus oocytes reveals a novel mechanism of mechanotransduction

Many animal cells release ATP into the extracellular medium, and often this release is mechanosensitive. However, the mechanisms underlying this release are not well understood. Using the luciferin-luciferase bioluminescent assay we demonstrate that a Xenopus oocyte releases ATP at a basal rate approximately 0.01 fmol/s, and gentle mechanical stimulation can increase this to 50 fmol/s. Brefeldin A, nocodazole, and progesterone-induced- maturation block basal and mechanosensitive ATP release. These treatments share the common feature of disrupting the Golgi complex and vesicle trafficking to the cell surface and thereby block protein secretion and membrane protein insertion. We propose that ATP release occurs when protein transport vesicles enriched in ATP fuse with the plasma membrane. Collagenase, integrin-binding peptides, and cytochalasin D also block ATP release, indicating that extracellular, membrane and cytoskeletal elements are involved in the release process. Elevation of intracellular Ca(2+) does not evoke ATP release but potentiates mechanosensitive ATP release. Our study indicates a novel mechanism of mechanotransduction that would allow cells to regulate membrane trafficking and protein transport/secretion in response to mechanical loading.

Requirement for efficient interactions between CD4 and MHC class II molecules for survival of resting CD4+ T lymphocytes in vivo and for activation-induced cell death

Regulation of homeostasis in the immune system includes mechanisms that promote survival of resting T lymphocytes, and others that control activation-induced cell death (AICD). In this study, we report on the use of a transgenic mouse model to test the role of CD4-MHC class II interactions for the susceptibility of CD4+ T lymphocytes to AICD, and for the survival of resting CD4+ T cells in peripheral lymphoid organs. The only I-Abeta gene expressed in these mice is an Abetak transgene with a mutation that prevents MHC class II molecules from interacting with CD4. We show increased apoptosis in CD4+ T lymphocytes derived from wild-type, but not from mutant Abetak transgenic mice following stimulation with staphylococcal enterotoxin A. Therefore, AICD may be impaired in CD4+ T cells derived from mutant Abetak transgenic mice. Importantly, we observed much higher apoptosis in resting CD4+ T cells from mutant Abetak transgenic mice than from wild-type mice. Furthermore, resting CD4+ T cells from mutant Abetak transgenic mice expressed higher levels of cell surface CD95 (Fas, APO-1). Ab-mediated cross-linking of CD95 further increased apoptosis in CD4+ T cells from mutant Abetak transgenic mice, but not from wild-type mice, suggesting apoptosis involved CD95 signaling. When cocultured with APC-expressing wild-type MHC class II molecules, apoptosis in resting CD4+ T lymphocytes from mutant Abetak transgenic mice was reduced. Our results show for the first time that interactions between CD4 and MHC class II molecules are required for the survival of resting CD4+ T cells in peripheral lymphoid organs.

Analogies and differences between omega-conotoxins MVIIC and MVIID: binding sites and functions in bovine chromaffin cells

The characteristics of the binding sites for the Conus magus toxins omega-conotoxin MVIIC and omega-conotoxin MVIID, as well as their effects on K+-evoked 45Ca2+ entry and whole-cell Ba2+ currents (IBa), and K+-evoked catecholamine secretion have been studied in bovine adrenal chromaffin cells. Binding of [125I] omega-conotoxin GVIA to bovine adrenal medullary membranes was displaced by omega-conotoxins GVIA, MVIIC and MVIID with IC50 values of around 0.1, 4 and 100 nM, respectively. The reverse was true for the binding of [125I] omega-conotoxin MVIIC, which was displaced by omega-conotoxins MVIIC, MVIID and GVIA with IC50 values of around 30, 80 and 1.200 nM, respectively. The sites recognized by omega-conotoxins MVIIC and MVIID in bovine brain exhibited higher affinities (IC50 values of around 1 nM). Both omega-conotoxin MVIIC and MVIID blocked IBa by 70-80%; the higher the [Ba2+]o of the extracellular solution the lower the blockade induced by omega-conotoxin MVIIC. This was not the case for omega-conotoxin MVIID; high Ba2+ (10 mM) slowed down the development of blockade but the maximum blockade achieved was similar to that obtained in 2 mM Ba2+. A further difference between the two toxins concerns their reversibility; washout of omega-conotoxin MVIIC did not reverse the blockade of IBa while in the case of omega-conotoxin MVIID a partial, quick recovery of current was produced. This component was irreversibly blocked by omega-conotoxin GVIA, suggesting that it is associated with N-type Ca2+ channels. Blockade of K+-evoked 45Ca2+ entry produced results which paralleled those obtained by measuring IBa. Thus, 1 microM of each of omega-conotoxin GVIA and MVIIA inhibited Ca2+ uptake by 25%, while 1 microM of each of omega-conotoxin MVIIC and MVIID caused a 70% blockade. K+-evoked catecholamine secretory responses were not reduced by omega-conotoxin GVIA (1 microM). In contrast, at 1 microM both omega-conotoxin MVIIC and MVIID reduced the exocytotic response by 70%. These data strengthen the previously established conclusion that Q-type Ca2+ channels that contribute to the regulation of secretion and are sensitive to omega-conotoxins MVIIC and MVIID are present in bovine chromaffin cells. These channels, however, seem to possess binding sites for omega-conotoxins MVIIC and MVIID whose characteristics differ considerably from those described to occur in the brain; they might represent a subset of Q-type Ca2+ channels or an entirely new subtype of voltage-dependent high-threshold Ca2+ channel.

BCL-2-related protein expression in apoptosis: oxidative stress versus serum deprivation in PC12 cells

Expression of the BCL-2 protein family members, BAX, BAK, BAD, BCL-xL, BCL-xS, and BCL-2, was measured (by western blotting using specific antibodies) in PC12 cells before and during apoptosis induced by either H2O2 treatment or by serum deprivation and during rescue from apoptosis by nerve growth factor (NGF). H2O2-induced apoptosis, as measured by DNA fragmentation, caused: (a) a dose-dependent increase in BAX, (b) a dose-independent increase in BAK, and (c) a dose-dependent inhibition of BAD expression. By comparison, apoptosis induced by serum deprivation resulted in a time-dependent decrease in both BAX and BAK, along with a dramatic and sudden decrease in BAD expression. However, when PC12 cells were incubated in an apoptosis-sparing medium (i.e., NGF-supplemented serum-free medium), both BAX and BAK were increased significantly, whereas BAD expression remained inhibited. BCL-xL expression was increased by H2O2 but unaffected by serum deprivation or long-term NGF treatment. Neither BCL-2 nor BCL-xS expression could be detected in PC12 cells under the experimental conditions tested. Our results show that the expression of BAX, BAK, BAD, and BCL-xL is altered in a stimulus-dependent manner but cannot be used to define whether a cell will undergo or survive apoptosis. The similarity between changes in expression of BCL-2-related proteins induced by H2O2 exposure and NGF rescue could reflect activation in part of a common antioxidant pathway.

The actions of ouabain and lithium chloride on cytosolic Ca2+ in single chromaffin cells

The effects of ouabain, Li+ and veratridine on the concentration of cytosolic free Ca2+ ([Ca2+]i) were studied in single fura-2-loaded bovine adrenal chromaffin cells. Superfusion of cells with ouabain (10 microM for 60 min) caused only a delayed mild increase of the Ca2+]i, from around 0.1 microM to 0.2-0.3 microM; this increase was Nao(+)-dependent. Replacement of all NaCl of the Krebs-Hepes solution by LiCl (144 mM) produced a gradual increase of [Ca2+]i, which remained elevated at a stable plateau of 0.4-0.5 microM for 40-50 min. When ouabain (in the presence of normal Nao+) or Li+ (in the absence of Nao+) was given in Krebs-Hepes solution containing no Ca2+, the reintroduction of 2.5 mM Ca2+ produced a fast elevation of the [Ca2+]i. In the case of ouabain-treated cells, the [Ca2+]i curve exhibited an initial phasic component which inactivated to a tonic component. omega-Conotoxin MVIIC (3 microM) and R56865 (10 microM) inhibited the phasic but not the tonic component. Veratridine (30 microM) induced large [Ca2+]i oscillations. Both ouabain or Li+ abolished such oscillations. These results are compatible with ouabain causing elevation of [Ca2+]i in bovine chromaffin cells through a dual mechanism, i.e. cell depolarisation and slowing down of the Na(+)-Ca2+ exchanger of their plasmalemma. Through its binding to the Na+ site on the Na(+)-Ca2+ exchanger, Li+ ions generate powerful Cai2+ signals that might be relevant to its known effects on neurosecretory mechanisms.

Effects of omega-conotoxin MVIIC on veratridine-induced cytotoxicity and cytosolic Ca(2+) oscillations

External Ca(2+) entry through various Ca(2+)-channel subtypes is responsible for the large oscillations of the cytosolic Ca(2+) concentrations, [Ca(2+)](i), and cell death induced by veratridine in primary cultures of bovine chromaffin cells. Blockade by omega-conotoxin GVIA (GVIA) of N-type Ca(2+) channels, by omega-agatoxin IVA (IVA) of P-type Ca(2+) channels, or by furnidipine of L-type Ca(2+) channels did not afford cytoprotection. However, (omega-conotoxin MVIIC (MVIIC), a wide-spectrum blocker of N-, P- and Q-type Ca(2+) channels greatly protected the cells against the cytotoxic effects of veratridine. Furnidipine further enhanced the cytoprotecting effects of MVIIC. MVIIC but not furuidipine, markedly reduced the oscillations of [Ca(2+)](i) induced by veratridine in single fura-2-loaded chromaffin cells. The results suggest that Ca(2+) entry through any of the different Ca(2+) channel subtypes present in bovine chromaffin cells might be cytotoxic. They also support two ideas: (i) that wide-spectrum neuronal Ca(2+) channel blockers (i.e. MVIIC) might be better cytoprotecting agents than more specific neuronal Ca(2+) channel blockers (i.e., GVIA, IVA, furnidipine); and (ii) that combined Ca(2+) channel blockers may provide greater cytoprotection than single compounds.

Contribution of SK and BK channels in the control of catecholamine release by electrical stimulation of the cat adrenal gland

1. Transmural electrical stimulation (10 Hz, 1 ms, 40 V for 10 s) of cat adrenal glands perfused at room temperature with Krebs-Hepes solution produced catecholamine secretory responses which were reproducible when stimulations were applied at 5 min intervals. Such responses were inhibited about 20% by atropine (1 microM) and 80% by hexamethonium (30 microM). Apamin (100 nM) increased the secretory response 2.5-fold in the presence of atropine and 8-fold in the presence of hexamethonium. 2. Potentiation by apamin of secretory responses evoked by 100-pulse trains was similar at 5, 10 and 20 Hz (about 2-fold). When glands were continuously stimulated at 3 Hz, apamin increased 4-fold the initial secretion plateau. Continuous stimulation at a higher frequency (20 Hz) produced a sharp secretory peak followed by a small, sustained plateau; apamin did not alter this plateau. Apamin also enhanced the secretory responses obtained with sustained stimulation with acetylcholine (10 or 200 microM). 3. Secretion peaks induced by brief acetylcholine pulses (10 microM for 10 s) applied to isolated and superfused cat adrenal chromaffin cells were enhanced more than 3-fold by 100 nM apamin. Charybdotoxin (10 nM) did not enhance these secretory peaks. 4. In perfused cat adrenal glands, charybdotoxin (10 nM) affected neither the secretion evoked by trains of electrical stimulation applied at different frequencies nor the secretion evoked by acetylcholine pulses. 5. In 0.5 mM [Ca2+]o, apamin enhanced 3-fold the secretion evoked by electrical stimulation trains of 100 pulses (10 Hz, 10 s) and almost 6-fold the acetylcholine (10 microM for 10 s)-induced secretion. In 5 mM Ca2+, apamin enhanced the secretory responses to electrical stimulation and acetylcholine 2- and 10-fold, respectively. Charybdotoxin enhanced 2.5-fold the secretory response to electrical stimulation in 0.5 mM Ca2+, although this effect was not statistically significant. A synergistic interaction between the two toxins on catecholamine release induced by electrical stimulation was observed at low but not at high [Ca2+]o. 6. Simultaneous release of acetylcholine and catecholamines upon electrical stimulation was achieved in glands in which the endogenous acetylcholine stores in the splanchnic nerve terminals had been prelabelled by perfusion with [3H]choline. While apamin enhanced more than 2-fold the postsynaptic release of catecholamines, the presynaptic release of acetylcholine remained unaffected. 7. The results are compatible with the hypothesis that, under physiological conditions, Ca(2+)-activated SK channels present in chromaffin cells control the firing patterns of action potentials induced by the acetylcholine released from splanchnic nerves during stress.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacological protection against the cytotoxicity induced by 6-hydroxydopamine and H2O2 in chromaffin cells

We present in this report the characteristics of the damage induced by 6-hydroxydopamine and H2O2 on bovine chromaffin cells in primary culture. Cytotoxicity was quantified using catecholamine cell contents, lactate dehydrogenase (LDH) release, trypan blue exclusion and morphological appearance. An excellent correlation between these four parameters was found. The cytotoxic effects of 6-hydroxydopamine were Ca(2+)-independent. In spite of this, the Ca2+ channel antagonists R56865 (N-[1-(4-(fluorophenoxy)butyl)]-4-piperidinyl-N-methyl-2-benzo-thiazo lamine) lidoflazine exhibited marked cytoprotective effects against both 6-hydroxydopamine and H2O2. The selective dopamine uptake blocker, bupropion, increased the viability of 6-hydroxydopamine and H2O2-treated cells from 20% to around 80%. Catalase drastically protected against the cytotoxic effects of 6-hydroxydopamine and H2O2. In contrast, desferrioxamine gave better protection against H2O2 cytotoxicity; glutathione and N-acetylcysteine only afforded substantial protection against 6-hydroxydopamine. Three main conclusions emerge from this study. (1st) 6-Hydroxydopamine causes chromaffin cell damage via a mechanism probably related to the production of free radicals, but unrelated to Ca2+ ions. Cytoprotection afforded by R56865 and lidoflazine must be unrelated to their Ca2+ antagonist properties. This suggests a novel component in the cytoprotective mechanism of action of these drugs. (2nd) The strong cytoprotective effects of bupropion seem to be unrelated to its ability to block the plasmalemmal dopamine carrier. (3rd) Bovine adrenal chromaffin cells in primary cultures are a suitable model for adult neurons to study the basic mechanism of cell damage, and to screen new drugs with putative neuroprotective properties.

Expression of the bovine striatal D2 receptor, but not the D1 receptor, in bovine adrenal medulla

At 37 degrees, the specific binding of [3H]SCH23390 to purified adrenal medullary plasma membranes accounted for only 20% of total binding. At 4 degrees, the binding did not saturate; therefore, equilibrium binding constants could not be estimated. Similar results were obtained with 125I-SCH23982, a ligand that exhibits 25-fold higher specific activity, compared with [3H]SCH23390. Of 11 dopamine receptor ligands used, only (+)-SCH23390 and (+/-)-SKF83566 inhibited the binding of [3H]SCH23390, but with very low affinities (IC50 values of 446 and 635 nM, respectively). In striatal membranes, binding of [3H]SCH23390 and of 125I-SCH23982 followed saturation isotherms. [3H]SCH23390 exhibited a Kd of 383 pM and a Bmax of 479 fmol/mg of protein, and 125I-SCH23982 exhibited a Kd of 664 pM and a Bmax of 453 fmol/mg of protein. The radioligand was displaced by the D1-selective compounds (+)-SCH23390 (IC50 of 3 nM), (+/-)-SKF83556 (IC50 of 5 nM), and (+)-SKF38393 (IC50 of 17 nM); spiperone and quinpirole were ineffective. [3H]Spiperone binding to bovine striatal and adrenal medullary plasma membranes exhibited similar characteristics, compatible with a typical D2 receptor. Northern blot analysis revealed the presence of D1 receptor mRNA in poly(A)+ RNA preparations from bovine brain striatum. When Northern blots containing poly(A)+ from bovine adrenal medulla were probed, no specific hybridization band for D1 receptors was observed; in contrast, a band of the expected size for D2 receptors was obtained. Similar results were obtained with in situ hybridization techniques and with more sensitive reverse transcription-polymerase chain reaction methods. The data support the idea that the peripheral D2 receptor present in bovine adrenal medulla is similar to striatal D2 receptors; in contrast, striatal D1 receptors do not seem to have a counterpart in bovine adrenal medullary tissues.

Effects of Ca2+ channel antagonists on chromaffin cell death and cytosolic Ca2+ oscillations induced by veratridine

Exposure of bovine chromaffin cells to 30 microM veratridine for 24 h led to 70-80% cell death as reflected by phase contrast microscopy, trypan blue exclusion, lactate dehydrogenase (LDH) release and cell catecholamine contents. Na+ deprivation, Ca2+ deletion or tetrodotoxin (5 microM) prevented the veratridine-induced cell damage. Nimodipine and verapamil, but not omega-conotoxin GVIA afforded 20-30% protection. Flunarizine protected the cells by 80% and R56865 by 60%. Stimulation of fura-2-loaded single bovine chromaffin cells with 30 microM of 1,1-dimethyl-4-phenylpiperazinium (DMPP) or 59 mM K+ caused fast increases in cytosolic Ca2+ concentrations, ([Ca2+]i). The [Ca2+]i rose from 0.1 to peaks of 1.9 microM, which quickly declined to near basal levels with a t1/2 of around 30 s. In spite of sustained stimulation with these two depolarizing agents, the [Ca2+]i remained low and did not undergo oscillations. In contrast, veratridine (30 microM) caused large and frequent oscillatory changes in the [Ca2+]i which were long-lasting and did not disappear even 30 min after washing out the toxin. The [Ca2+]i oscillations were reversibly suppressed by Na+ or Ca2+ removal and by 5 microM tetrodotoxin. Selective L-type Ca2+ channel blockers (10 microM nimodipine or verapamil) or N-type Ca2+ channel blockers (1 microM omega-conotoxin GVIA) did not affect the [Ca2+]i oscillations. In contrast, flunarizine or R56865 (10 microM each) suppressed the oscillations of [Ca2+]i. The results demonstrate that bovine chromaffin cells have the necessary machinery to develop prolonged and repetitive [Ca2+]i oscillations in the presence of veratridine; however, 'physiological' depolarizing stimuli did not cause oscillations.(ABSTRACT TRUNCATED AT 250 WORDS)

A component of the catecholamine secretory response in the bovine adrenal gland is resistant to dihydropyridines and omega-conotoxin

Acetylcholine (ACh, 100 microM)-evoked catecholamine release from perfused bovine adrenal glands was unaffected by CTX (0.3 microM) and depressed 70% by nisoldipine (1 microM). Combined CTX plus nisoldipine did not inhibit further the secretory response K+ (150 mM)-evoked secretion was diminished 30% by CTX and 20% by nisoldipine. Combined CTX plus nisoldipine inhibited secretion by 35%. Cd2+ blocked the K(+)-evoked secretory response by over 90%. Bay K 8644 (1 microM) enhanced the basal output of catecholamines and clearly potentiated the secretory responses to mild concentrations of ACh (3 microM) or K+ (17.7 mM). The results suggest that in addition to CTX- and DHP-sensitive Ca2+ channels, a third Ca2+ pathway might contribute to the entry of external Ca2+ into chromaffin cells necessary to trigger the exocytotic catecholamine release response in the bovine adrenal gland.

Functional involvement of α1and α2-adrenoceptors in86Rb efflux from liver slices and lipolysis in guinea-pig isolated adipocytes

1. The application of an alpha 1-adrenoceptor agonist, amidephrine, to guinea-pig liver slices increases glucose release and 86Rb efflux. Since prazosin was more potent than yohimbine in inhibiting both responses, alpha 1-adrenoceptors seem to be involved in the effects evoked by the agonist. 2. Clonidine (an alpha 2-adrenoceptor agonist) at doses unable to activate liver glycogenolysis increased 86Rb release and potentiated isoprenaline in promoting 86Rb efflux. Since yohimbine antagonized clonidine in promoting 86Rb efflux, alpha 2-adrenoceptors also seem to control plasmalemmal permeability to 86Rb. 3. The liver slice responses resulting from alpha 1- and alpha 2-adrenoceptor stimulation required extracellular calcium. Calcium absence or the administration of D-600 attenuated the effects of amidephrine on glucose release and 86Rb outflow and Ca2+ excess re-established both responses. D-600 and apamin blocked clonidine-induced 86Rb efflux, suggesting that alpha 2-adrenoceptor stimulation activates calcium dependent K+ channels. 4. alpha 2-adrenoceptors do not appear to mediate antilipolytic effects in guinea-pig fat cells.

Alpha- and beta-adrenoceptor cross-talk in the regulation of glycogenolysis in dog and guinea-pig liver

The dog liver glycogenolytic response to isoprenaline (EC50 = 3 x 10(-9) M) was selectively blocked by 10(-5) M of practolol, but not by butoxamine. In contrast, the glycogenolytic response to isoprenaline (EC50 = 3 x 10(-7) M) was inhibited by 10(-6) M of butoxamine, but not by practolol, in the guinea-pig liver. This suggests that, in the dog, the isoprenaline response is dominated by beta 1-adrenoceptors, while in the guinea-pig beta 2-receptors control such response. Glucose release from dog and guinea-pig liver slices was also stimulated by amidephrine (EC50 = 10(-6) M in the dog and 4 x 10(-5) M in the guinea-pig). Both prazosin and yohimbine blocked this response. The effectiveness of clonidine as a glucose-mobilizing agent could only be established in the dog liver. Prazosin showed greater activity than yohimbine in antagonizing the response to both agonists. In the dog, low concentrations of alpha-adrenoceptor agonists (10(-9) M), that failed to modify the basal glucose release per se, selectively depressed the isoprenaline response. Prazosin, but not yohimbine, reversed this inhibitory effect. It is concluded that glucose release from the dog liver is regulated by two opposite mechanisms that seem to be associated to alpha 1-adrenoceptors (inhibitory) and to beta 1-adrenoceptors (stimulatory).

Membrane-mediated effects of the steroid 17-alpha-estradiol on adrenal catecholamine release

The effects of 17-alpha-estradiol on the secretion of catecholamines from the perfused bovine and cat adrenal gland and bovine chromaffin cells in culture elicited by dimethylphenylpiperazinium (DMPP), methacholine and high potassium were studied. In perfused cat adrenal glands, secretion of catecholamines evoked by pulses of DMPP (1 microM for 30 sec) was decreased by 17-alpha-estradiol at concentrations of 1 and 10 microM by 50 and 80%, respectively. However, secretion evoked by pulses of methacholine (3 microM for 30 sec) was not affected by 1 microM of 17-alpha-estradiol and was affected to a variable extent by 10 microM 17-alpha-estradiol. Catecholamine secretion evoked by higher concentrations of methacholine (100 microM for 60 sec) was reduced by 50% by 10 microM 17-alpha-estradiol. 17-alpha-Estradiol decreased secretion evoked by pulses of 120 mM K+ for 10 sec to a similar extent in the perfused bovine and cat adrenal gland. The 45Ca++ uptake into bovine chromaffin cells in culture stimulated by DMPP (100 microM for 10 sec) or high K+ (59 mM for 10 sec) was almost inhibited completely by 100 microM 17-alpha-estradiol. The rapid action precludes a classical genomic mechanism and suggests effects at the cell membrane.