Restitution of defective glucose-stimulated insulin release of sulfonylurea type 1 receptor knockout mice by acetylcholine

Inhibition of ATP-sensitive K+ (K(ATP)) channels by an increase in the ATP/ADP ratio and the resultant membrane depolarization are considered essential in the process leading to insulin release (IR) from pancreatic beta-cells stimulated by glucose. It is therefore surprising that mice lacking the sulfonylurea type 1 receptor (SUR1-/-) in beta-cells remain euglycemic even though the knockout is expected to cause hypoglycemia. To complicate matters, isolated islets of SUR1-/- mice secrete little insulin in response to high glucose, which extrapolates to hyperglycemia in the intact animal. It remains thus unexplained how euglycemia is maintained. In recognition of the essential role of neural and endocrine regulation of IR, we evaluated the effects of acetylcholine (ACh) and glucagon-like peptide-1 (GLP-1) on IR and free intracellular Ca2+ concentration ([Ca2+]i) of freshly isolated or cultured islets of SUR1-/- mice and B6D2F1 controls (SUR1+/+). IBMX, a phosphodiesterase inhibitor, was also used to explore cAMP-dependent signaling in IR. Most striking, and in contrast to controls, SUR1-/-) islets are hypersensitive to ACh and IBMX, as demonstrated by a marked increase of IR even in the absence of glucose. The hypersensitivity to ACh was reproduced in control islets by depolarization with the SUR1 inhibitor glyburide. Pretreatment of perifused SUR1-/- islets with ACh or IBMX restored glucose stimulation of IR, an effect expectedly insensitive to diazoxide. The calcium channel blocker verapamil reduced but did not abolish ACh-stimulated IR, supporting a role for intracellular Ca2+ stores in stimulus-secretion coupling. The effect of ACh on IR was greatly potentiated by GLP-1 (10 nM). ACh caused a dose-dependent increase in [Ca2+]i at 0.1-1 microM or biphasic changes (an initial sharp increase in [Ca2+]i followed by a sustained phase of low [Ca2+]i) at 1-100 microM. The latter effects were observed in substrate-free medium or in the presence of 16.7 mM glucose. We conclude that SUR1 deletion depolarizes the beta-cells and markedly elevates basal [Ca2+]i. Elevated [Ca2+]i in turn sensitizes the beta-cells to the secretory effects of ACh and IBMX. Priming by the combination of high [Ca2+]i, ACh, and GLP-1 restores the defective glucose responsiveness, precluding the development of diabetes but not effectively enough to cause hyperinsulinemic hypoglycemia.     

Phosphodiesterase type 5 inhibition improves early memory consolidation of object information

The nitric oxide (NO)-cyclic GMP (cGMP) signaling pathway is assumed to play an important role in processes underlying learning and memory. We used phosphodiesterase type 5 (PDE5) inhibitors to study the role of cGMP in object- and spatial memory. Our results and those reported in other studies indicate that elevated hippocampal cGMP levels are required to improve the memory performance of rodents in object recognition and passive avoidance learning, but not in spatial learning. The timing of treatment modulates the effects on memory and strongly supports a role for cGMP in early stages of memory formation. Alternative explanations for the improved memory performance of PDE5 inhibitors are also discussed. Immunocytochemical studies showed that in vitro slice incubations with PDE5 inhibitors increase NO-stimulated cGMP levels mainly in hippocampal varicose fibers. Reviewing the available data on the localization of the different components of the NO-cGMP signaling pathway, indicates a complex interaction between NO and cGMP, which may be independent of each other. It is discussed that further studies are needed, immunocytochemical and behavioral, to better understand the cGMP-mediated molecular mechanisms underlying memory formation.     

Severely incapacitating mutations in patients with extreme short stature identify RNA-processing endoribonuclease RMRP as an essential cell growth regulator

The growth of an individual is deeply influenced by the regulation of cell growth and division, both of which also contribute to a wide variety of pathological conditions, including cancer, diabetes, and inflammation. To identify a major regulator of human growth, we performed positional cloning in an autosomal recessive type of profound short stature, anauxetic dysplasia. Homozygosity mapping led to the identification of novel mutations in the RMRP gene, which was previously known to cause two milder types of short stature with susceptibility to cancer, cartilage hair hypoplasia, and metaphyseal dysplasia without hypotrichosis. We show that different RMRP gene mutations lead to decreased cell growth by impairing ribosomal assembly and by altering cyclin-dependent cell cycle regulation. Clinical heterogeneity is explained by a correlation between the level and type of functional impairment in vitro and the severity of short stature or predisposition to cancer. Whereas the cartilage hair hypoplasia founder mutation affects both pathways intermediately, anauxetic dysplasia mutations do not affect B-cyclin messenger RNA (mRNA) levels but do severely incapacitate ribosomal assembly via defective endonucleolytic cleavage. Anauxetic dysplasia mutations thus lead to poor processing of ribosomal RNA while allowing normal mRNA processing and, therefore, genetically separate the different functions of RNase MRP.     

A cardiovascular-respiratory control system model including state delay with application to congestive heart failure in humans

This paper considers a model of the human cardiovascular-respiratory control system with one and two transport delays in the state equations describing the respiratory system. The effectiveness of the control of the ventilation rate is influenced by such transport delays because blood gases must be transported a physical distance from the lungs to the sensory sites where these gases are measured. The short term cardiovascular control system does not involve such transport delays although delays do arise in other contexts such as the baroreflex loop (see [46]) for example. This baroreflex delay is not considered here. The interaction between heart rate, blood pressure, cardiac output, and blood vessel resistance is quite complex and given the limited knowledge available of this interaction, we will model the cardiovascular control mechanism via an optimal control derived from control theory. This control will be stabilizing and is a reasonable approach based on mathematical considerations as well as being further motivated by the observation that many physiologists cite optimization as a potential influence in the evolution of biological systems (see, e.g., Kenner [29] or Swan [62]). In this paper we adapt a model, previously considered (Timischl [63] and Timischl et al. [64]), to include the effects of one and two transport delays. We will first implement an optimal control for the combined cardiovascular-respiratory model with one state space delay. We will then consider the effects of a second delay in the state space by modeling the respiratory control via an empirical formula with delay while the the complex relationships in the cardiovascular control will still be modeled by optimal control. This second transport delay associated with the sensory system of the respiratory control plays an important role in respiratory stability. As an application of this model we will consider congestive heart failure where this transport delay is larger than normal and the transition from the quiet awake state to stage 4 (NREM) sleep. The model can be used to study the interaction between cardiovascular and respiratory function in various situations as well as to consider the influence of optimal function in physiological control system performance.Supported by FWF (Austria) under grant F310 as a subproject of the Special Research Center F003 Optimization and ControlMathematics Subject Classification (2000): 92C30, 49J15     

Mnd2, an essential antagonist of the anaphase-promoting complex during meiotic prophase

Meiotic cohesin serves in sister chromatid linkage and DNA repair until its subunit Rec8 is cleaved by separase. Separase is activated when its inhibitor, securin, is polyubiquitinated by the Cdc20 regulated anaphase-promoting complex (APC(Cdc20)) and consequently degraded. Differently regulated APCs (APC(Cdh1), APC(Ama1)) have not been implicated in securin degradation at meiosis I. We show that Mnd2, a factor known to associate with APC components, prevents premature securin degradation in meiosis by APC(Ama1). mnd2Delta cells lack linear chromosome axes and exhibit precocious sister chromatid separation, but deletion of AMA1 suppresses these defects. Besides securin, Sgo1, a protein essential for protection of centromeric cohesion during anaphase I, is also destabilized in mnd2delta cells. Mnd2's disappearance prior to anaphase II may activate APC(Ama1). Human oocytes may spend many years in meiotic prophase before maturation. Inhibitors of meiotic APC variants could prevent loss of chiasmata also in these cells, thereby guarding against aberrant chromosome segregation.     

A novel assay of cell rubidium uptake using graphite furnace atomic absorption: application to rats on a magnesium-deficient diet

The [Na,K]ATPase or sodium pump (SP) is a ubiquitous membrane cation transport system. Because of its potential participation in the pathophysiology of essential hypertension and cataract formation, the SP is under active investigation to detail its function and control. In this paper, we describe a novel, nonradioactive method of measuring SP ion transport activity in intact red blood cells (RBCs) using graphite furnace atomic absorption measurement of rubidium ion (Rb) uptake. This method provided sensitivity comparable to radioactive techniques, as assessed by experiments with human red blood cells (RBC) and ouabain, a known SP inhibitor, but this analytical approach eliminates the use of radioisotopes common to other Rb uptake assay methods. As a demonstration of its broader utility, the assay was used to assess the effects of dietary magnesium intake on SP-mediated ion transport in the RBCs of diet-controlled rats. Rats on 7 weeks of a magnesium-deficient (MgD) diet showed significant reductions in serum magnesium concentration, although levels remained in the lower region of the reference interval for healthy, magnesium replete animals. Red cell Rb uptake was significantly reduced in cells from the magnesium-restricted animals, demonstrating the sensitivity of Rb uptake to reduced magnesium intake, despite serum levels that fell within the reported normal range, and the utility of this Rb uptake assay in measuring physiological changes in SP function.     

Monophyly of primary photosynthetic eukaryotes: green plants, red algae, and glaucophytes

Between 1 and 1.5 billion years ago, eukaryotic organisms acquired the ability to convert light into chemical energy through endosymbiosis with a Cyanobacterium (e.g.,). This event gave rise to "primary" plastids, which are present in green plants, red algae, and glaucophytes ("Plantae" sensu Cavalier-Smith). The widely accepted view that primary plastids arose only once implies two predictions: (1) all plastids form a monophyletic group, as do (2) primary photosynthetic eukaryotes. Nonetheless, unequivocal support for both predictions is lacking (e.g.,). In this report, we present two phylogenomic analyses, with 50 genes from 16 plastid and 15 cyanobacterial genomes and with 143 nuclear genes from 34 eukaryotic species, respectively. The nuclear dataset includes new sequences from glaucophytes, the less-studied group of primary photosynthetic eukaryotes. We find significant support for both predictions. Taken together, our analyses provide the first strong support for a single endosymbiotic event that gave rise to primary photosynthetic eukaryotes, the Plantae. Because our dataset does not cover the entire eukaryotic diversity (but only four of six major groups in), further testing of the monophyly of Plantae should include representatives from eukaryotic lineages for which currently insufficient sequence information is available.