Does cyclic AMP mobilize Ca2+ for amylase secretion from rat parotid cells?

Both dibutyryl cAMP and carbachol stimulated amylase are released from rat parotid cells incubated in Ca²⁺-free medium containing 1 mM EGTA. Cells preincubated with 10 μM carbachol in Ca²⁺-free, 1 mM EGTA medium for 15 min lost responsiveness to carbachol, but maintained responsiveness to dibutyryl cAMP. Dibutyryl cAMP still evoked amylase release from cells preincubated with 1 μM ionophore A23187 and 1 mM EGTA for 20 min. Although carbachol stimulated net efflux of ⁴⁵Ca from cells preequilibrated with ⁴⁵Ca for 30 min, dibutyryl cAMP did not elicit any apparent changes in the cellular ⁴⁵Ca level. Inositol trisphosphate, but not cAMP, evoked ⁴⁵Ca release from saponin-permeabilized cells. These results suggest that cAMP does not mobilize calcium for amylase release from rat parotid cells.     

Does cyclic AMP mobilize Ca2+ for amylase secretion from rat parotid cells?

Both dibutyryl cAMP and carbachol stimulated amylase released from rat parotid cells incubated in Ca2+-free medium containing 1 mM EGTA. Cells preincubated with 10 microM carbachol in Ca2+-free, 1 mM EGTA medium for 15 min lost responsiveness to carbachol, but maintained responsiveness to dibutyryl cAMP. Dibutyryl cAMP still evoked amylase release from cells preincubated with 1 microM ionophore A23187 and 1 mM EGTA for 20 min. Although carbachol stimulated net efflux of 45Ca from cells preequilibrated with 45Ca for 30 min, dibutyryl cAMP did not elicit any apparent changes in the cellular 45Ca level. Inositol trisphosphate, but not cAMP, evoked 45Ca release from saponin-permeabilized cells. These results suggest that cAMP does not mobilize calcium for amylase release from rat parotid cells.     

Does intracellular histamine mediate mast cell histamine release?

Previously, we demonstrated that through binding a novel intracellular receptor of microM affinity (HIC), histamine mediates, and the HIC antagonist N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine. HCl (DPPE) inhibits, platelet aggregation and serotonin granule secretion; the latter response is dependent upon the same processes that mediate histamine release from mast cell granules. We now show that, as for platelet serotonin release, DPPE blocks concanavalin A-stimulated mast cell histamine release with a potency (IC50 = 30 microM) greater than the H1-antagonist, pyrilamine (IC50 = 150 microM) or the H2-antagonist cimetidine (IC50 = 5 mM), correlating with rank order of potency to inhibit 3H-histamine binding in rat brain membranes and liver microsomes. We postulate that histamine release from mast cells is mediated at HIC by second messenger intracellular histamine. However, unlike platelets, mast cells do not appear to rely on newly synthesized histamine. Rather, as for calcium, histamine may be mobilized from bound stores to mediate histamine secretion.     

Does protein kinase C activation mediate thrombin-induced arachidonate release in human platelets?

Thrombin stimulated rapid formation of diacylglycerol, inositol 1,4,5-trisphosphate (IP3) and thromboxane B2 (TXB2) in human platelets. Formation of diacylglycerol and IP3 appeared to precede that of TXB2. Activation of protein kinase C by diacylglycerol combining with Ca+2 mobilization by IP3 has been implicated in mediating arachidonate release. However, addition of the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7) to platelet suspension did not inhibit thrombin-stimulated arachidonate release and TXB2 synthesis, whereas addition of the Ca+2 antagonist, 3,4,5-trimethoxybenzoic acid 8-(diethylamino) octyl ester (TMB-8) or the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) abolished arachidonate release. The correlation of IP3 production with arachidonate release on increasing the concentrations of thrombin was further examined. IP3 production reached near maximum at 0.2 U/ml, whereas TXB2 synthesis continued to increase at 1 U/ml. These results suggest that protein kinase C activation may not mediate arachidonate release and that Ca+2 mobilization by IP3 may only partially account for arachidonate release in platelets stimulated with relatively high concentrations of thrombin.     

Does the hypothalamic tyrosine-hydroxylase inhibition mediate the positive feedback of progesterone on gonadotropin release in women?

Neuropharmacological studies suggest a common inhibitory role for the hypothalamic dopaminergic pathway on gonadotropin and prolactin pituitary release, in humans. As a consequence, it has been hypothesized that the inhibition of hypothalamic tyrosine-hydroxylase and the subsequent fall in dopamine synthesis is involved in the positive feedback of progesterone on LH and PRL pituitary release in estrogen-primed hypogonadal women. The aim of our study was to verify whether an inhibition of tyrosine-hydroxylase may really account for the progesterone action on gonadotropin and prolactin secretion. For this purpose, we compared the effect of a specific tyrosine-hydroxylase inhibitor (alpha-methyl-p-tyrosine, AMPT) with the effect of progesterone on gonadotropin and prolactin release in estrogen-primed postmenopausal women. Progesterone induced a marked release of LH (delta: 129.7 +/- 16.5 mlU/ml, mean +/- SE) and a slight increase in FSH (delta: 39.4 +/- 11.6 mlU/ml) and PRL (delta: 15.3 +/- 2.8 ng/ml) serum levels. Acute or two-day administration of AMPT was followed by a marked rise in PRL serum levels (delta: 82.9 +/- 13.8 and 88.3 +/- 8.2 ng/ml, respectively) while there were no significant increases in serum LH (delta: 5.4 +/- 2.6 and 3.3 +/- 4.6 mlU/ml) and FSH (delta: 3.4 +/- 0.9 and -0.4 +/- 2.9) concentrations. The ineffectiveness of a specific tyrosine-hydroxylase inhibitor in simulating the progesterone effect on gonadotropin secretion seems to negate the hypothesis that a reduction in hypothalamic dopaminergic activity mediates the positive feedback of progesterone on gonadotropin release.     

Does plant community plasticity mediate microbial homeostasis?

Microbial homeostasis—constant microbial element ratios along resource gradients—is a core ecological tenet, yet not all systems display homeostasis. We suggest investigations of homeostasis mechanisms must also consider plant–microbial interactions. Specifically, we hypothesized that ecosystems with strong plant community plasticity to changing resources will have homeostatic microbial communities, with less microbial resource cost, because plants reduce variance in resource stoichiometry. Using long‐term nutrient additions in two ecosystems with differing plant response, we fail to support our hypothesis because although homeostasis appears stronger in the system with stronger plant response, microbial mechanisms were also stronger. However, our conclusions were undermined by high heterogeneity in resources, which may be common in ecosystem‐level studies, and methodological assumptions may be exacerbated by shifting plant communities. We propose our study as a starting point for further ecosystem‐scale investigations, with higher replication to address microbial and soil variability, and improved insight into microbial assimilable resources.     

Does serotonin deficit mediate susceptibility to ADHD?

The onset of attention-deficit-hyperactivity-disorder (ADHD) in childhood is characterized by developmentally inappropriate levels of hyperactivity, impulsivity and inattention. A chronic deficit of serotonin (5-HT) at the synapse may trigger symptoms of ADHD. This review focuses on neuro-anatomical, experimental and clinical pharmacological evidence, as well as the genetic underpinnings of serotoninergic involvement in the etiology of ADHD. Neuro-anatomical investigations suggest that serotonin through the orbitofrontal–striatal circuitry may regulate behavioral domains of hyperactivity and impulsivity in ADHD. Studies from animal models of ADHD indicate intimate interplay between 5-HT and dopaminergic neurotransmission. Selective serotonin re-uptake inhibitors, as also non-stimulant drugs acting on the 5-HT system are, however, clinically effective. They impart less severe side effects in patients with no risk of addiction. Oral administration of l-tryptophan, the amino acid precursor of 5-HT, significantly alleviates ADHD symptoms. Given the multifactorial nature of ADHD, candidate gene and genome-wide association studies have suggested that serotoninergic gene variants are associated with increased risk of ADHD with each locus individually exerting a modest effect on overall risk.     

Does my mouse have Alzheimer's disease?

Small animal models that manifest many of the characteristic neuropathological and behavioral features of Alzheimer's disease (AD) have been developed and have proven of great value for studying the pathogenesis of this disorder at the molecular, cellular and behavioral levels. The great progress made in our understanding of the genetic factors that either cause or contribute to the risk of developing AD has prompted many laboratories to create transgenic (tg) mice that overexpress specific genes which cause familial forms of the disease. Several of these tg mice display neuropathological and behavioral features of AD including amyloid β-peptide (Aβ) and amyloid deposits, neuritic plaques, gliosis, synaptic alterations and signs of neurodegeneration as well as memory impairment. Despite these similarities, important differences in neuropathology and behavior between these tg mouse models and AD have also been observed, and to date no perfect animal model has emerged. Moreover, ascertaining which elements of the neuropathological and behavioral phenotype of these various strains of tg mice are relevant to that observed in AD continues to be a challenge. Here we provide a critical review of the AD-like neuropathology and behavioral phenotypes of several well-known and utilized tg mice that express human APP transgenes.     

Does osmotic regulation of amylase activity in bean cotyledons exist?

The hypothesis that the promotive effect of the embryo axis of the germinating bean seed on amylase activity in the cotyledons is mediated by an osmoregulative mechanism was examined. After 2 days of germination the action of the axis on amylolytic activity was already clearly revealed, whereas at the same time it did not have any influence on osmotic pressure in the cotyledons. When the axis was attached to one cotyledon during 4 days of incubation, osmotic pressure in the cotyledon was lower than its value in the cotyledons of the intact seedling, whereas amylolytic activity was similar in both treatments. It was concluded that the tested hypothesis is not valid in the case of the bean seedling. External osmotic agents brought about a decrease in the level of amylase in the cotyledons, but this does not prove that osmotic changes which are brought about by production of internal metabolites are involved in the regulation of amylase synthesis.     

Computational genetics: from mouse to human?

In this article, we describe a novel computational-analysis method that rapidly identified the genetic basis for several trait differences among inbred mouse strains. This approach enables researchers to identify a causative genetic factor by correlating a pattern of observable physiological or pathological differences among selected inbred strains with a pattern of genetic variation. Compared with conventional methods used for mouse genetic analysis, which require many years to produce results, this haplotype-based computational analysis can be rapidly performed. We discuss the factors affecting the performance and precision of this computational method. Although it currently can analyze traits of limited genetic complexity in mouse, the potential application of this genetic-analysis method to other experimental organisms, and possibly humans, is evaluated.     

Does life history mediate changing disease risk when communities disassemble?

Biodiversity loss sometimes increases disease risk or parasite transmission in humans, wildlife and plants. Some have suggested that this pattern can emerge when host species that persist throughout community disassembly show high host competence – the ability to acquire and transmit infections. Here, we briefly assess the current empirical evidence for covariance between host competence and extirpation risk, and evaluate the consequences for disease dynamics in host communities undergoing disassembly. We find evidence for such covariance, but the mechanisms for and variability around this relationship have received limited consideration. This deficit could lead to spurious assumptions about how and why disease dynamics respond to community disassembly. Using a stochastic simulation model, we demonstrate that weak covariance between competence and extirpation risk may account for inconsistent effects of host diversity on disease risk that have been observed empirically. This model highlights the predictive utility of understanding the degree to which host competence relates to extirpation risk, and the need for a better understanding of the mechanisms underlying such relationships.     

Does leukotriene C4 mediate hypoxic vasoconstriction in isolated ferret lungs?

To evaluate leukotriene (LT) C4 as a mediator of hypoxic pulmonary vasoconstriction, we examined the effects of FPL55712, a putative LT antagonist, and indomethacin, a cyclooxygenase inhibitor, on vasopressor responses to LTC4 and hypoxia (inspired O2 tension = 25 Torr) in isolated ferret lungs perfused with a constant flow (50 ml.kg-1.min-1). Pulmonary arterial injections of LTC4 caused dose-related increases in pulmonary arterial pressure during perfusion with physiological salt solution containing Ficoll (4 g/dl). FPL55712 caused concentration-related inhibition of the pressor response to LTC4 (0.6 micrograms). Although 10 micrograms/ml FPL55712 inhibited the LTC4 pressor response by 61%, it did not alter the response to hypoxia. At 100 microgram/ml, FPL55712 inhibited the responses to LTC4 and hypoxia by 73 and 71%, respectively, but also attenuated the vasoconstrictor responses to prostaglandin F2 alpha (78% at 8 micrograms), phenylephrine (68% at 100 micrograms), and KCl (51% at 40 mM). At 0.5 microgram/ml, indomethacin significantly attenuated the pressor response to arachidonic acid but did not alter responses to LTC4 or hypoxia. These results suggest that in isolated ferret lungs 1) the vasoconstrictor response to LTC4 did not depend on release of cyclooxygenase products and 2) LTC4 did not mediate hypoxic vasoconstriction.     

What do we know about gliotransmitter release from astrocytes?

Astrocytes participate in information processing by actively modulating synaptic properties via gliotransmitter release. Various mechanisms of astrocytic release have been reported, including release from storage organelles via exocytosis and release from the cytosol via plasma membrane ion channels and pumps. It is still not fully clear which mechanisms operate under which conditions, but some of them, being Ca²⁺-regulated, may be physiologically relevant. The properties of Ca²⁺-dependent transmitter release via exocytosis or via ion channels are different and expected to produce different extracellular transmitter concentrations over time and to have distinct functional consequences. The molecular aspects of these two release pathways are still under active investigation. Here, we discuss the existing morphological and functional evidence in support of either of them. Transgenic mouse models, specific antagonists and localization studies have provided insight into regulated exocytosis, albeit not in a systematic fashion. Even more remains to be uncovered about the details of channel-mediated release. Better functional tools and improved ultrastructural approaches are needed in order fully to define specific modalities and effects of astrocytic gliotransmitter release pathways.