Author
Halvor N. Christensen
Other affiliations: Umeå University, Tufts University
Bio: Halvor N. Christensen is an academic researcher from University of Michigan. The author has contributed to research in topics: Amino acid & Alanine. The author has an hindex of 56, co-authored 186 publications receiving 11115 citations. Previous affiliations of Halvor N. Christensen include Umeå University & Tufts University.
Topics: Amino acid, Alanine, Glycine, Leucine, Arginine
Papers published on a yearly basis
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1,058 citations
801 citations
TL;DR: Especially significant in view of the importance of glutamine metabolism are an insensitivity of the new system to stimulation by either insulin or glucagon, and its distinct enhancement on starvation of the cells with respect to amino acids, suggesting a second system has been found to show adaptive regulation.
395 citations
TL;DR: It is concluded that the new component of transport in the Ehrlich cell shows a distinctly lower pH sensitivity, a somewhat lower sensitivity to metabolic inhibitors, and a much higher stereo-specificity than the A system.
319 citations
TL;DR: The present study considers the question whether such model amino acids gain access to the diaphragm atypically, and what kind of an entry process insulin modifies.
300 citations
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TL;DR: The lipid composition of the vesicles shows the high sphingomyelin content characteristic of sheep red cell plasma membranes, but not white cell or platelet membranes, consistent with the conclusion that the vESicles are of reticulocyte origin.
2,167 citations
TL;DR: Afhnity for Monovalent Cations and Quantitative Relation between Effect of Na+ + K+ on Enzyme System and Active Transport in Intact Cell.
Abstract: Afhnity for Monovalent Cations. 597 Relationship of Enzyme System to ATP. 598 Isolation of Enzyme System from Other Cells with Active Transport of Na+ and K+ 602 Location of Enzyme System in the Cell. 604 Effect of Cardiac Glycosides. 605 Quantitative Relation between Effect of Na+ + K+ on Enzyme System and Active Transport in Intact Cell. 606 Nature of Enzyme System. 607 Relation of (Na + + K+)-Activated Enzyme System to Active Transport of Cations. 6 10 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6’4
1,946 citations
TL;DR: An overview of the biological importance of GSH at the level of the cell and organism can be found in this article, where the authors provide a review of the most prevalent non-protein thiol in animal cells.
1,716 citations
TL;DR: In cardiac myocytes, and probably other cell types, the exchanger serves a housekeeping role by maintaining a low intracellular Ca2+ concentration; its possible role in cardiac excitation-contraction coupling is controversial.
Abstract: The Na+/Ca2+ exchanger, an ion transport protein, is expressed in the plasma membrane (PM) of virtually all animal cells. It extrudes Ca2+ in parallel with the PM ATP-driven Ca2+ pump. As a reversible transporter, it also mediates Ca2+ entry in parallel with various ion channels. The energy for net Ca2+ transport by the Na+/Ca2+ exchanger and its direction depend on the Na+, Ca2+, and K+ gradients across the PM, the membrane potential, and the transport stoichiometry. In most cells, three Na+ are exchanged for one Ca2+. In vertebrate photoreceptors, some neurons, and certain other cells, K+ is transported in the same direction as Ca2+, with a coupling ratio of four Na+ to one Ca2+ plus one K+. The exchanger kinetics are affected by nontransported Ca2+, Na+, protons, ATP, and diverse other modulators. Five genes that code for the exchangers have been identified in mammals: three in the Na+/Ca2+ exchanger family (NCX1, NCX2, and NCX3) and two in the Na+/Ca2+ plus K+ family (NCKX1 and NCKX2). Genes homologous to NCX1 have been identified in frog, squid, lobster, and Drosophila. In mammals, alternatively spliced variants of NCX1 have been identified; dominant expression of these variants is cell type specific, which suggests that the variations are involved in targeting and/or functional differences. In cardiac myocytes, and probably other cell types, the exchanger serves a housekeeping role by maintaining a low intracellular Ca2+ concentration; its possible role in cardiac excitation-contraction coupling is controversial. Cellular increases in Na+ concentration lead to increases in Ca2+ concentration mediated by the Na+/Ca2+ exchanger; this is important in the therapeutic action of cardiotonic steroids like digitalis. Similarly, alterations of Na+ and Ca2+ apparently modulate basolateral K+ conductance in some epithelia, signaling in some special sense organs (e.g., photoreceptors and olfactory receptors) and Ca2+-dependent secretion in neurons and in many secretory cells. The juxtaposition of PM and sarco(endo)plasmic reticulum membranes may permit the PM Na+/Ca2+ exchanger to regulate sarco(endo)plasmic reticulum Ca2+ stores and influence cellular Ca2+ signaling.
1,715 citations
TL;DR: Dysregulation of GSH synthesis is increasingly being recognized as contributing to the pathogenesis of many pathological conditions, including diabetes mellitus, pulmonary fibrosis, cholestatic liver injury, endotoxemia and drug-resistant tumor cells.
1,712 citations