Statistics for Spatial Data.

Publisher Summary This chapter discusses preparation of isolated rat liver cells The early mechanical and chemical methods for liver-cell preparation were relatively successful in converting liver tissue to a suspension of isolated cells The successful preparation of intact liver cells by perfusion with collagenase is technically quite difficult The major method for preparation of nonparenchymal liver cells is based on the selective sensitivity of parenchymal cells toward proteases By incubation of rat liver minces with pronase, most of the liver parenchyma is digested, while nonparenchymal cells remain intact and can be recovered from the incubate Similar results have been reported with trypsin digestion of collagenase-dispersed liver minces, but pronase appears to be more effective The most common procedure is to perfuse the liver briefly with pronase before it is minced and incubated with the enzyme Such direct pronase methods have been used by several investigators with yields of nonparenchymal liver cells reported to be in the range 2–15 × 10 6 cells/gm liver

Preparation of isolated rat liver cells.

▪ Abstract Synaptic transmission is a dynamic process. Postsynaptic responses wax and wane as presynaptic activity evolves. This prominent characteristic of chemical synaptic transmission is a crucial determinant of the response properties of synapses and, in turn, of the stimulus properties selected by neural networks and of the patterns of activity generated by those networks. This review focuses on synaptic changes that result from prior activity in the synapse under study, and is restricted to short-term effects that last for at most a few minutes. Forms of synaptic enhancement, such as facilitation, augmentation, and post-tetanic potentiation, are usually attributed to effects of a residual elevation in presynaptic [Ca2+]i, acting on one or more molecular targets that appear to be distinct from the secretory trigger responsible for fast exocytosis and phasic release of transmitter to single action potentials. We discuss the evidence for this hypothesis, and the origins of the different kinetic phases...

/pdf/short-term-synaptic-plasticity-5d4dx79319.pdf

Short-Term Synaptic Plasticity

[This corrects the article on p. 100 in vol. 41.].

Energy conservation in chemotrophic anaerobic bacteria.

Tissue hypoxia results from an inadequate supply of oxygen (O(2)) that compromises biologic functions. Evidence from experimental and clinical studies increasingly points to a fundamental role for hypoxia in solid tumors. Hypoxia in tumors is primarily a pathophysiologic consequence of structurally and functionally disturbed microcirculation and the deterioration of diffusion conditions. Tumor hypoxia appears to be strongly associated with tumor propagation, malignant progression, and resistance to therapy, and it has thus become a central issue in tumor physiology and cancer treatment. Biochemists and clinicians (as well as physiologists) define hypoxia differently; biochemists define it as O(2)-limited electron transport, and physiologists and clinicians define it as a state of reduced O(2) availability or decreased O(2) partial pressure that restricts or even abolishes functions of organs, tissues, or cells. Because malignant tumors no longer execute functions necessary for homeostasis (such as the production of adequate amounts of adenosine triphosphate), the physiology-based definitions of the term "hypoxia" are not necessarily valid for malignant tumors. Instead, alternative definitions based on clinical, biologic, and molecular effects that are observed at O(2) partial pressures below a critical level have to be applied.

/pdf/tumor-hypoxia-definitions-and-current-clinical-biologic-and-5gkgj1718s.pdf

Tumor hypoxia: definitions and current clinical, biologic, and molecular aspects.

An optical method for measurement of dioxygen concentration based upon quenching of phosphorescence.

The imaging of phosphorescence provides a method for monitoring oxygen distribution within the vascular system of intact tissues. Isolated rat lives were perfused through the portal vein with media containing palladium coproporphyrin, which phosphoresced and was used to image the liver at various perfusion rates. Because oxygen is a powerful quenching agent for phosphors, the transition from well-perfused liver to anoxia (no flow of oxygen) resulted in large increases of phosphorescence. During stepwise restoration of oxygen flow, the phosphorescence images showed marked heterogeneous patterns of tissue reoxygenation, which indicated that there were regional inequalities in oxygen delivery.

http://science.sciencemag.org/content/sci/241/4873/1649.full.pdf

Imaging of phosphorescence: a novel method for measuring oxygen distribution in perfused tissue

One of the characteristic features of living matter is its ability to generate metabolic energy which is required for growth and the maintenance of multiple cellular functions. The major pathways whereby eukaryotic organisms produce energy are glycolysis and mitochondrial oxidative phosphorylation; the latter process, which involves complete combustion of glucose to carbon dioxide and water, yields approximately 17 times as much useful energy as does anaerobic production of lactic acid (glycolysis). Owing to its high energy yield, mitochondrial oxidative phosphorylation is responsible for supplying over 95% of the total ATP requirement in eukaryotic cells. All living organisms are steady-state systems in which the rate of energy production (ATP synthesis) equals the rate of energy utilization (except in rapid transient conditions in which this may not necessarily be true). This means that precise dynamic balance is maintained between the reactions which produce ATP and those which utilize it in which the concentration of ATP in the cell remains at an essentially constant level. Any decline in the usage of ATP causes an immediate decrease in the rate of its synthesis and vice versa. The range of activities over which mitochondrial oxidative phosphorylation operates in vivo is best illustrated by the observation that in man the rate of ATP synthesis varies from 0.4 g ATP/min/kg body weight at rest to 9.0 g ATP/min/kg body weight during strenuous exercise. This high flux through the ATP synthesizing pathway and its large dynamic range ensures that oxidative phosphorylation plays a paramount role in cellular homeostasis. In eukaryotic cells, the enzymes of oxidative phosphorylation are intimately associated with or form an integral part of the mitochondrial inner membrane (for review see Lehninger, 1966; Wainio, 1970). The site of ATP synthesis (ATP synthase) is located on the internal surface of the inner membrane and communicates with the matrix space. It is well known that the mitochondrial matrix houses but a few reactions which require ATP whereas the cytosol is the main site of ATP utilization. Mechanisms must, therefore, be present which allow the mitochondrial matrix to sense the need of the cytosol for an appropriate rate of ATP generation. Moreover, ATP has to be supplied under conditions for which its hydrolysis is sufficiently exergonic to do the required metabolic work (i.e., its hydrolysis has to provide a negative free energy change of sufficient magnitude). Since the maximum work that ATP hydrolysis can do is dependent on the [ATP]/[ADP] [Pi], variations in the cellular concentrations of ATP, ADP, and inorganic phosphate provide a very sensitive means through which homeostatic mechanisms can regulate energy production. The mitochondrial respiratory chain is a multienzyme complex which accepts reducing equivalents from NADH and FADH z and transfers them in a sequence of oxidation-reduction reactions to molecular oxygen with the formation of water and concomitant synthesis of ATP. In cells in vivo, reducing equivalents are provided through dehydrogenation of various substrates which are generated by the metabolic feeder pathways such as the tricarboxylic acid cycle or fatty acid oxidation system. Since mitochondrial dehydrogenases utilize either NAD or FAD as reducible coenzymes the amounts of NADH and FADH2 formed by the particular tissue depend on relative activities of these pathways, but in most cells NADH is the

David F. Wilson

Papers

An optical method for measurement of dioxygen concentration based upon quenching of phosphorescence.

Imaging of phosphorescence: a novel method for measuring oxygen distribution in perfused tissue

Regulation of cellular energy metabolism.

The oxygen dependence of mitochondrial oxidative phosphorylation measured by a new optical method for measuring oxygen concentration.

The oxygen dependence of cellular energy metabolism