Renal ammonium production--une vue canadienne

The purpose of this review is to examine the factors regulating ammonium production in the kidney and to place these factors in the perspective of acid-base balance. Renal ammonium production and excretion are required to maintain acid-base balance. However, only a portion of renal ammonium production is specifically stimulated by metabolic acidosis. One should examine urinary ammonium excretion at three levels: distribution of ammonium between blood and urine, augmented glutamine metabolism, and an energy constraint due to ATP balance considerations. With respect to the biochemical regulation of acid-base renal ammonium production, an acute stimulation of alpha-ketoglutarate dehydrogenase by a fall in pH seems to be important but this may not be the entire story. In chronic metabolic acidosis augmented glutamine entry into mitochondria (dog) or increased phosphate-dependent glutaminase activity (rat) become critical to support a high flux rate. Metabolic alterations, which diminish the rate of oxidation of alternate fuels, might also be important. The above principles are discussed in the ketoacidosis of fasting, the clinically important situation of high rates of renal ammonium production.     

Subcellular localization of chicken liver xanthine dehydrogenase. A possible source of cytoplasmic reducing equivalents.

Classical fractionation studies showed that xanthine dehydrogenase (EC 1.2.1.37) was exclusively cytosolic in chicken liver. Fumarase (EC 4.2.1.2) and malate dehydrogenase (EC 1.1.1.37) were also found to have major cytosolic locations. These data indicate that urate synthesis in chicken liver produces substantial quantities of cytoplasmic NADH which may supply reducing equivalents of gluconeogenesis and other processes.     

What behaviour in economic games tells us about the evolution of non-human species' economic decision-making behaviour

In the past decade, there has been a surge of interest in using games derived from experimental economics to test decision-making behaviour across species. In most cases, researchers are using the games as a tool, for instance, to understand what factors influence decision-making, how decision-making differs across species or contexts, or to ask broader questions about species’ propensities to cooperate or compete. These games have been quite successful in this regard. To what degree, however, do these games tap into species'' economic decision-making? For the purpose of understanding the evolution of economic systems in humans, this is the key question. To study this, we can break economic decision-making down into smaller components, each of which is a potential step in the evolution of human economic behaviour. We can then use data from economic games, which are simplified, highly structured models of decision-making and therefore ideal for the comparative approach, to directly compare these components across species and contexts, as well as in relation to more naturalistic behaviours, to better understand the evolution of economic behaviour and the social and ecological contexts that influenced it. The comparative approach has successfully informed us about the evolution of other complex traits, such as language and morality, and should help us more deeply understand why and how human economic systems evolved.This article is part of the theme issue ‘Existence and prevalence of economic behaviours among non-human primates’.     

Calcium channels and signal transduction in plant cells

An increasing number of studies indicate that changes in cytosolic free Ca²⁺ ([Ca²⁺]_c) mediate specific types of signal transduction in plant cells. Modulation of [Ca²⁺]_c is likely to be achieved through changes in the activity of Ca²⁺ channels, which catalyse passive influx of Ca²⁺ to the cytosol from extracellular and intracellular compartments. Voltage-sensitive Ca²⁺ channels have been detected in the plasma membranes of algae, where they control membrane electrical properties and cell turgor. These channels are sensitive to 1,4-dihydropyridines, which in animal cells specifically affect one class of voltage-regulated plasma membrane Ca²⁺ channel. Ca²⁺-permeable channels with different pharmacological properties have been found in the plasma membrane of higher plants. Recent evidence suggests the existence of two discrete classes of Ca²⁺ channel co-resident in the vacuolar membrane (tonoplast) of higher plants. The first is gated by inositol 1,4,5-trisphosphate, and bears a number of similarities to its animal counterpart which is located in the endoplasmic reticulum (ER). The second tonoplast Ca²⁺ channel is voltage-operated. However, the specific roles of these tonoplast channels in signal transduction have yet to be elucidated.