Is cyclic AMP involved in the defibrillating effect of sotalol ?

Ventricular fibrillation induced in animals pretreated with sotalol, a class III antiarrhythmic agent, would spontaneously terminate and revert into a sinus rhythm. This phenomenon has been atributed to the class III action of this Drug, I.e., prolongation of myocardial action potential duration and effective refractory period. Since various observations suggested that these alone cannot explain the defibrillating phenomenon, we hypothesised that sotalol affeced ventricular intercellular synchronization by increasing intercellular coupling. Our recent experimental studies have shown that sotalol antagonized the cellular decoupling to guinea pig ventricular muscle strip caused by perfusion with either a hypoxic normal Tyrode's solution or an oxygenated high Ca2+ Tyrode's solution. We assumed that the most likely mechanism for the restoration of intercellular coupling would be by increasing intracellular cAMP concentration. In order to test this hypothesis, we studied the modification of this sotalol-induced recoupling by a cAMP dependent protein kinase inhibitor. The results clearly supported our assumption since the addition of Arg-Gly-Tyr-Ala-Leu-Gly (pure A- kinase inhibitor) prevented the aforementioned cellular recoupling action of sotalol in a dose-dependent manner. It can thus be concluded that changes in intracellular cAMP level are involved in the synchronizing /defibrillating effect of sotalol.     

Is cholinergic activity of the caudate nucleus involved in memory?

A review was made of experiments dealing with the involvement of cholinergic activity of the caudate nucleus in memory processes. Injections of acetylcholine-receptor blockers or of neurotoxins against cholinergic interneurons into the striatum produce marked impairments in acquisition and retention of instrumental tasks while injections of acetylcholine or choline into the caudate produce the opposite effect. However, after a period of overtraining cholinergic blockade or interference with neural activity of the caudate does not produce significant deficits in retention. It is concluded that striatal cholinergic activity is critically involved in memory of recent events and that long-term memory is mediated by different neurochemical systems outside the caudate nucleus.     

Is the Rsp5 ubiquitin ligase involved in the regulation of ribophagy?

Under nutrient limiting conditions, cytoplasmic components are randomly sequestered into double-membrane vesicles called autophagosomes and delivered to the lysosome/vacuole for degradation and recycling. In the last few years, however, it has been observed that several cytoplasmic components such as organelles, pathogens or specific protein complexes can also be selectively targeted for degradation by autophagy-related pathways (reviewed in reference 1). We have recently shown that in S. cerevisiae, mature ribosomes are subject to such selective degradation by autophagy under starvation conditions, in a process that we termed ‘ribophagy’.² By genetic screening, we found that selective degradation of 60S large ribosomal subunits depends on the ubiquitin protease Ubp3 and its cofactor Bre5, implying that ribophagy is regulated by ubiquitin-dependent steps. Interestingly, several ubiquitinated proteins accumulate in ribosome fractions isolated from ubp3? cells, suggesting that the regulation of ribophagy by ubiquitin may be direct. Here we present data on a potential role of the ubiquitin ligase Rsp5 as a positive regulator of ribophagy, and discuss the possible involvement of ubiquitin as a signaling molecule in this process.

Addendum to: Kraft C, Deplazes A, Sohrmann M, Peter M. Mature ribosomes are selectively degraded upon starvation by an autophagy pathway requiring the Ubp3p/Bre5p ubiquitin protease. Nat Cell Biol 2008; 10:602-10.     

Are separable aromatase systems involved in hormonal regulation of the male brain?

In vitro study of testosterone (T) metabolism shows that formation of estradiol-17β (E₂) is regionally specific within the preoptic area (POA) of the male ring dove. The POA is known to be involved in the formation of E₂ required for specific components of male sexual behavior. Two sub-areas of high aromatase activity, anterior (aPOA) and posterior preoptic (pPOA) areas, have been identified. Aromatase activity is higher in aPOA than in pPOA. The aromatase activity within the aPOA is also more sensitive to the inductive effects of low circulating T, derived from subcutaneous silastic implants, than the enzyme activity in pPOA. Kinetic analysis of preoptic fractions indicates that a similar high-affinity enzyme occurs in both areas (apparent K_m < 14nM), but the V_max of aPOA enzyme activity is higher than pPOA. Cells containing estrogen receptors (ER) are localized in areas of high aromatase activity. There is overlap between immunostained cells in the aPOA and in samples containing inducible aromatase activity measured in vitro. Within the aPOA there is a higher density of ER cells in the nucleus preopticus medialis. The pPOA area also contains ER, notably in the nucleus interstitialis, but at a lower density. We conclude that the hormonal regulation of the male preoptic-anterior hypothalamic region, which is a target for the behavioral action of T, involves at least two inducible aromatase systems with associated estrogen receptor cells.     

Is the Rsp5 ubiquitin ligase involved in the regulation of ribophagy?

Under nutrient limiting conditions, cytoplasmic components are randomly sequestered into double-membrane vesicles called autophagosomes and delivered to the lysosome/vacuole for degradation and recycling. In the last few years, however, it has been observed that several cytoplasmic components such as organelles, pathogens or specific protein complexes can also be selectively targeted for degradation by autophagy-related pathways (reviewed in ref. 1). We have recently shown that in S. cerevisiae, mature ribosomes are subject to such selective degradation by autophagy under starvation conditions, in a process that we termed 'ribophagy.'(2) By genetic screening, we found that selective degradation of 60S large ribosomal subunits depends on the ubiquitin protease Ubp3 and its cofactor Bre5, implying that ribophagy is regulated by ubiquitin-dependent steps. Interestingly, several ubiquitinated proteins accumulate in ribosome fractions isolated from ubp3Delta cells, suggesting that the regulation of ribophagy by ubiquitin may be direct. Here we present data on a potential role of the ubiquitin ligase Rsp5 as a positive regulator of ribophagy, and discuss the possible involvement of ubiquitin as a signaling molecule in this process.     

Are separable aromatase systems involved in hormonal regulation of the male brain?

In vitro study of testosterone (T) metabolism shows that formation of estradiol-17 beta (E2) is regionally specific within the preoptic area (POA) of the male ring dove. The POA is known to be involved in the formation of E2 required for specific components of male sexual behavior. Two sub-areas of high aromatase activity, anterior (aPOA) and posterior preoptic (pPOA) areas, have been identified. Aromatase activity is higher in aPOA than in pPOA. The aromatase activity within the aPOA is also more sensitive to the inductive effects of low circulating T, derived from subcutaneous silastic implants, than the enzyme activity in pPOA. Kinetic analysis of preoptic fractions indicates that a similar high-affinity enzyme occurs in both areas (apparent Km less than 14 nM), but the Vmax of aPOA enzyme activity is higher than pPOA. Cells containing estrogen receptors (ER) are localized in areas of high aromatase activity. There is overlap between immunostained cells in the aPOA and in samples containing inducible aromatase activity measured in vitro. Within the aPOA there is a higher density of ER cells in the nucleus preopticus medialis. The pPOA area also contains ER, notably in the nucleus interstitialis, but at a lower density. We conclude that the hormonal regulation of the male preoptic-anterior hypothalamic region, which is a target for the behavioral action of T, involves at least two inducible aromatase systems with associated estrogen receptor cells.     

Is CYP1B1 involved in the metabolism of dioxins in the pig?

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most difficult to biodegradate and the most toxic dioxin congener. Previously, we demonstrated in silico the ability of pig CYP1A1 to hydroxylate 2,7-dichlorodibenzo-p-dioxin (DiCDD), but not TCDD. To increase our knowledge concerning the low effectiveness of TCDD biodegradability, we analyzed in silico the binding selectivity and affinity between pig CYP1B1 and the two dioxins by means of molecular modeling. We also compared the effects of TCDD and DiCDD on CYP1B1 gene expression (qRT-PCR) and catalytic (EROD) activity in porcine granulosa cells. It was found that DiCDD and TCDD were stabilized within the pig CYP1B1 active site by hydrophobic interactions. The analysis of substrate channel availability revealed that both dioxins opened the exit channel S, allowing metabolites to leave the enzyme active site. Moreover, DiCDD and TCDD increased the CYP1B1 gene expression and catalytic activity in porcine granulosa cells. On the other hand, TCDD demonstrated higher than DiCDD calculated affinity to pig CYP1B1, hindering TCDD exit from the active site. The great distance between CYP1B1's heme and TCDD also might contribute to the lower hydroxylation effectiveness of TCDD compared to that of DiCDD. Moreover, the narrow active site of pig CYP1B1 may immobilize TCDD molecule, inhibiting its hydroxylation. The results of the access channel analysis and the distance from pig CYP1B1's heme to TCDD suggest that the metabolizing potential of pig CYP1B1 is higher than that of pig CYP1A1. However, this potential is probably not sufficiently high to considerably improve the slow TCDD biodegradation.     

Is light quality involved in the regulation of the photosynthetic apparatus in attached rice leaves?

The regulatory effect of light quality on the photosynthetic apparatus in attached leaves of rice plants was investigated by keeping rice plants under natural light, in complete darkness, or under illumination with light of different colors. When leaves were left in darkness and far-red (FR)-light conditions for 6 days at 30°C, there was an initial lag in chlorophyll (Chl) content, Chl a/b ratio, and maximum photosystem (PS) II photochemistry that lasted until the second day; these then rapidly decreased on the fourth day. In contrast, ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) rapidly disappeared with no lag under low or zero light conditions. By using spectrophotometric quantitation, it was determined that the PSII and PSI reaction centers were regulated by light quality, but cytochrome (Cyt) f was regulated by light intensity. However, the PSII heterogeneity was also strongly modified by the light intensity; PSIIα with the large antenna decreased markedly both in content and in antenna size. Consequently, the PSIIα/PSI ratio declined under FR-light because the low intensity of FR-light dominated over its quality in the modulation of the PSIIα/PSI ratio. An imbalance between them induced the generation of reactive oxygen species (ROS), although the ROS were scavenged by stromal enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). The activities of these stromal enzymes are also regulated by light quality. Thus, although the photosynthetic apparatus is regulated differently depending on light quality, light quality may play an important role in the regulation of the photosynthetic apparatus.     

Is mucus involved in biocrystallization?

Summary Freeze-dried intestinal mucus of sea-water-adapted eels was analysed by scanning electron microscopy (SEM) and X-ray microanalysis. Calcite crystals were observed in the mucus fibres; their concentration increased along the hindgut. Random SEM observations made in situ indicated that mucus fibres were involved in the genesis of these crystals. Calcium-rich mucus globules were found fused inside crystal matrices. Single typical rhombohedric crystals of various complexity appeared within the mucus framework. The steps of crystal biogenesis were reconstituted in in-vitro conditions.     

Is actin involved in the nuclear division in Amoeba proteus?

During semi-open mitosis of Amoeba proteus the nuclear envelope is not dispersed and nucleus divides by fission. The presence of actin layer close to nuclear envelope was demonstrated in interphase and telophase nuclei of that amoeba stained with rhodamine labelled phalloidin. In telophase, an accumulation of actin arises in the space between the future daughter nuclei. It appears to be comparable with the contractile ring of dividing cells. This suggests that actin associated with the nuclear envelope of Amoeba proteus may be involved in final separation of the daughter nuclei, forming a constriction ring at the middle of dividing nucleus.     

Is the renin-angiotensin system involved in urinary concentration mechanisms?

Renin release elicited by i.v. injection of loop-diuretics was used to study the effects of angiotensin II (AII) on intrarenal hemodynamics. The vasoconstrictive action of intrarenally synthesized AII predominates in the efferent glomerular arteriole. Such a vasoconstrictive effect could affect blood flow in the vasa recta which stem from efferent arterioles of juxtamedullary glomeruli. Renin secretion and renal inner medullary blood flow (tissue clearance of 133Xe) were simultaneously measured before and after frusemide-induced renin release. The relationship between renin secretion and renal inner medullary blood flow was inverse. Changes in renal medullary blood flow may be physiological determinants of medullary osmolality and renal concentration ability. The intrarenal role of AII in urinary concentration recovery after frusemide was examined. Inhibition of renin release by propranolol or AII-blockade (by saralasin or Hoe 409) delayed recovery of urinary osmolality. In the conscious rat, propranolol slowed down recovery of the cortico-papillary gradient for sodium. Its vasoconstrictive action on the efferent glomerular arteriole might enable the renin-angiotensin system to participate in the control of renal excretion of salt and water.     

Are gonadal steroid hormones involved in disorders of brain aging?

Human aging is associated with a decrease of circulating gonadal steroid hormones. Since these hormones act as trophic factors for neurones and glia, it is possible that the decrease in sex steroid levels may contribute to the increased risk of neurodegenerative disorders with advanced age. Sex steroids are neuroprotective in several animal models of central and peripheral neurodegenerative diseases, and clinical data suggest that these hormones may reduce the risk of neural pathology in aged humans. Potential therapeutic approaches for aged-associated neural disorders may emerge from studies conducted to understand the mechanisms of action of sex steroids in the nervous system of aged animals. Alterations in the endogenous capacity of the aged brain to synthesize and metabolize sex steroids, as well as possible aged-associated modifications in the signalling of sex steroid receptors in the nervous system, are important areas for future investigation.     

Is astrocyte laminin involved in axon guidance in the mammalian CNS?

This paper provides evidence for the expression of laminin on glia in correlation with axon elongation and nerve pathway formation during embryonic development of the mouse optic nerve and other parts of the central nervous system (CNS). We show that punctate deposits of laminin on immature glial cells precede the entrance of the first optic axons into the nerve, and remain in close association with growing axons. Furthermore, we show that in one particular region of the optic pathway that the retinal ganglion cell axons avoid in normal animals (i.e., the pigmented area of the distal nerve) the punctate laminin matrix is missing. As the optic nerve matures punctate laminin deposits disappear, and laminin is reduced in the astroglial cytoplasm. The close correlation of the punctate form of laminin with early axonal growth is true not only in the optic nerve but also in some other parts of the CNS. We demonstrate such punctate laminin deposits in a model of astrocyte-induced regeneration of the corpus callosum in acallosal mice (G. Smith, R. Miller, and J. Silver, 1986, J. Comp. Neurol. 251, 23-43), and in glia associated with several normal developing axon trajectories, such as the corpus callosum, fornix, and pathways in the embryonic hindbrain. In all of these regions punctate laminin deposits are found on astroglia that are associated with early growing axons. Our results indicate that the punctate form of laminin, produced by astrocytes, may be an important factor involved in axon elongation and nerve pathway formation in the mammalian CNS.     

Is there a gender difference of somatostatin-receptor density in the human brain?

Animal experiments and observations in human brains have convincingly shown that sexual differentiation not only concerns the genitalia but also the brain. This has been investigated also in the light of a possible explanation of a presumed biological aetiology of transsexuality. The volume of the central subdivision of the bed nucleus of the stria terminalis, a brain area that is essential for sexual behaviour, has been reported to be larger in men than in women. Additionally, the number of somatostatin expressing neurons in this region was shown to be higher in men than in women. As neuronal production of somatostatin is involved the idea is striking whether somatostatin-receptor density in the cortex of cerebral hemispheres might be related to gender identity. We investigated in vivo the density of somatostatin-receptors in selected regions of the human brain in both sexes by means of receptor scintigraphy. Basal ganglia tracer uptake of 111-In-Pentreotide was equally low in both genders at 0,80% +/ 0,26 (related to tracer uptake of the whole brain layer). Temporal cortex accumulated at 2,9% +/ 1,1 in men and at 2,3% +/ 0,76 in women. Frontal brain region had an uptake of 3,0% +/ 1,4 in male and of 2,5% +/ 1,3 in female. This shows a tendency in males for relatively augmented uptake indicating higher somatostatin receptor density in temporal and frontal cerebral cortex.     

Is 5-aminolevulinic acid involved in the hepatocellular carcinogenesis of acute intermittent porphyria?

5-Aminolevulinic acid (ALA) is a heme precursor that accumulates in acute intermittent porphyria (AIP) due to enzymatic deficiencies in the heme biosynthetic pathway Its accumulation has been associated with several symptoms, such as abdominal pain attacks, neuromuscular weaknesses, neuropsychiatric alterations and increased hepatocellular carcinoma (HCC) incidence. The use of exogenous ALA to elevate porphyrin levels in tumor photodynamic therapy, adds further significance to ALA toxicology. Under ferritin mediated and metal catalyzed oxidation, ALA produces reactive oxygen species that can damage plasmid and isolated DNA in vitro, and increases the steady-state level of 8-oxo-7,8-dihydro-2'-deoxyguanosine in liver, spleen and kidney DNA and 5-hydroxy-2'-deoxycytidine in liver DNA of ALA-treated rats. The in vitro DNA damage could be partially inhibited by SOD, catalase, DTPA, mannitol and melatonin. ALA also promotes the formation of radical-induced base degradation products in isolated DNA. 4,5-Dioxovaleric acid, the final oxidation product of ALA, alkylates guanine moieties within both nucleoside and isolated DNA, producing two diastereoisomeric adducts. Dihydropyrazine derivatives of ALA generated by its dimerization, promote DNA strand-breaks and 8-oxodGuo formation in the presence of Cu2+. Together these results reinforce the hypothesis that the DNA damage induced by ALA may be associated with the development of HCC in individuals suffering from AIP.