Glucose metabolism is vital to most mammalian cells, and the passage of glucose across cell membranes is facilitated by a family of integral membrane transporter proteins, the GLUTs. There are currently 14 members of the SLC2 family of GLUTs, several of which have been the focus of this series of reviews. The subject of the present review is GLUT3, which, as implied by its name, was the third glucose transporter to be cloned (Kayano T, Fukumoto H, Eddy RL, Fan YS, Byers MG, Shows TB, Bell GI. J Biol Chem 263: [15245][15246][15247][15248] 1988) and was originally designated as the neuronal GLUT. The overriding question that drove the early work on GLUT3 was why would neurons need a separate glucose transporter isoform? What is it about GLUT3 that specifically suits the needs of the highly metabolic and oxidative neuron with its high glucose demand? More recently, GLUT3 has been studied in other cell types with quite specific requirements for glucose, including sperm, preimplantation embryos, circulating white blood cells, and an array of carcinoma cell lines. The last are sufficiently varied and numerous to warrant a review of their own and will not be discussed here. However, for each of these cases, the same questions apply. Thus, the objective of this review is to discuss the properties and tissue and cellular localization of GLUT3 as well as the features of expression, function, and regulation that distinguish it from the rest of its family and make it uniquely suited as the mediator of glucose delivery to these specific cells.neurons; sperm; preimplantation embryo; white blood cells GLUCOSE METABOLISM IS VITAL to most mammalian cells, and the passage of glucose across cell membranes is facilitated by a family of integral membrane transporter proteins, the GLUTs. There are currently 14 members of the SLC2 family of GLUTs, several of which have been the focus of this series of reviews. The subject of the present review is GLUT3 which, as implied by its name, was the third glucose transporter to be cloned (62) and was originally designated as the neuronal glucose transporter. Together with GLUT1, -2, and -4, it comprises the Class 1 group of transporters (For review see Refs. 15,81,121). With the cloning of GLUT3, it became apparent that the brain did not rely exclusively on GLUT1 and that GLUT3 was highly and specifically expressed by neurons. Thus, GLUT3 became the third facilitative glucose transporter isoform with unique characteristics suited for cell-specific expression and function. GLUT2 is ideally suited for expression in liver and pancreas due to its high K m for glucose; GLUT4 and its translocation from intracellular vesicles to the cell surface facilitates insulin-stimulated glucose uptake in insulin-sensitive cells: muscle and fat. The overriding question that drove the early work in GLUT3 in the brain was: why would neurons need a separate glucose transporter isoform; what is it about GLUT3 that specifically suits the needs of the highly metabolic and oxidative neuron with its high glucose demand?...

This study investigates how changes in the level of cellular cholesterol affect inwardly rectifying K+ channels belonging to a family of strong rectifiers (Kir2). In an earlier study we showed that an increase in cellular cholesterol suppresses endogenous K+ current in vascular endothelial cells, presumably due to effects on underlying Kir2.1 channels. Here we show that, indeed, cholesterol increase strongly suppressed whole-cell Kir2.1 current when the channels were expressed in a null cell line. However, cholesterol level had no effect on the unitary conductance and only little effect on the open probability of the channels. Moreover, no cholesterol effect was observed either on the total level of Kir2.1 protein or on its surface expression. We suggest, therefore, that cholesterol modulates not the total number of Kir2.1 channels in the plasma membrane but rather the transition of the channels between active and silent states. Comparing the effects of cholesterol on members of the Kir2.x family shows that Kir2.1 and Kir2.2 have similar high sensitivity to cholesterol, Kir2.3 is much less sensitive, and Kir2.4 has an intermediate sensitivity. Finally, we show that Kir2.x channels partition virtually exclusively into Triton-insoluble membrane fractions indicating that the channels are targeted into cholesterol-rich lipid rafts.

Protein tyrosine phosphorylation is an important intracellular event accompanying the in-vitro capacitation of mouse, bovine and human spermatozoa. Here, we demonstrate that bovine serum albumin (BSA) and NaHCO(3) are required for protein tyrosine phosphorylation in ejaculated human spermatozoa. The absence of protein tyrosine phosphorylation in media minus these two constituents could be recovered by addition to the media of cAMP analogues and/or phosphodiesterase inhibitors. Since BSA is postulated to modulate capacitation by removal of cholesterol from the sperm plasma membrane, we determined whether cholesterol release leads to changes in protein tyrosine phosphorylation. Incubation of spermatozoa in media containing BSA resulted in the release of significant amounts of cholesterol when compared with media devoid of BSA. Preloading BSA with cholesterol-SO(4) inhibited protein tyrosine phosphorylation, as well as capacitation, and this inhibitory effect was overcome by the addition of dibutyryl cAMP plus isobutylmethylxanthine (IBMX). The functional significance of BSA-mediated cholesterol release, protein tyrosine phosphorylation and capacitation was confirmed by examining the effects of the cholesterol-binding heptasaccharides, methyl-beta-cyclodextrin or OH-propyl-beta-cyclodextrin. Both cyclodextrins caused cholesterol efflux from the spermatozoa, increased protein tyrosine phosphorylation, and stimulated capacitation. Therefore, cholesterol release is associated with the activation of a signal transduction pathway involving protein kinase A and tyrosine kinase second messenger systems, and resulting in protein tyrosine phosphorylation and capacitation.

This paper introduces a special feature on biodiversity conservation and poverty traps. We define and explain the core concepts and then identify four distinct classes of mechanisms that define important interlinkages between biodiversity and poverty. The multiplicity of candidate mechanisms underscores a major challenge in designing policy appropriate across settings. This framework is then used to introduce the ensuing set of papers, which empirically explore these various mechanisms linking poverty traps and biodiversity conservation.development | ecosystem | natural resources | sustainability | wildlife S temming biodiversity loss and reducing poverty are global challenges of the first order, enshrined in both the Convention on Biological Diversity and the Millennium Development Goals, agreed by virtually all countries over the past decade. The world is nonetheless struggling to meet the ambitions expressed in those global accords. The World Wide Fund for Nature International finds that the earth's wildlife populations have declined by a third over the past 35 y alone but by even more, 60%, in poorer tropical regions (1). The rate and magnitude of these losses will define the earth's sixth mass extinction period unless we quickly reverse this decline (2). Meanwhile, leaving aside the remarkable case of China, the number of people living in extreme poverty increased by more than 30% from 1981 to 2004 and now surpasses 1 billion (3).The persistence of extreme poverty and continued rapid loss of biodiversity appear intimately related. Extreme poverty and biodiversity hot spots are geographically coincident, concentrated in rural areas where livelihoods depend disproportionately on natural capital embodied in forests, rangelands, soils, water, and wildlife. Colocation naturally gives rise to closely coupled human-managed ecosystems that are in a precarious balance at best. Lack of resources, institutions, and governance structures often leaves local people illequipped to institute mechanisms to ensure long-term resource maintenance. Compounding this problem, the conditions of the human and nonhuman species within ecosystems coevolve in response to subtle shifts in any of several subsystems.Despite the importance of this coevolutionary relationship, connections between poverty traps and biodiversity conservation remain remarkably underexplored, not only in formal theorizing* but especially empirically. We have surprisingly little observational or experimental detail describing interactions in closely coupled human and natural systems in the rural tropics. In the absence of rigorous evidence on the synergies or tradeoffs between biodiversity conservation and escape from poverty traps, opinion and untested hypotheses predominate and crucial linkages are too often overlooked. Conservationists typically ignore the predictable consequences of human agency; people adapt behaviors in response to changes in environmental management, often generating unintended consequences that undermine conservation objectives (6). Simi...