In previous papers (Randle & Smith, 1958a, b) evidence was presented that insulin, anoxia and substances such as salicylate or 2:4-dinitrophenol, which inhibit oxidative phosphorylation, increase the uptake of glucose and D-xylose by isolated rat diaphragm by accelerating the transfer of these sugars across the muscle-cell membrane. The conclusion was drawn that the transfer process for sugars in muscle is inhibited by a substance generated during oxidative phosphorylation and that insulin activates the transfer process by interfering with the action of this substance.

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Chamber-stress equations relate wall stresses to pressure and wall dimensions. Such equations play a central role in the analysis and understanding of heart-chamber function. Over the past three decades, several stress equations giving radically different results have been derived, used, and/or espoused. They can be classified into two categories, according to the definition of stress underlying the equation. The stresses in one class of equations are total forces per unit normal area, excluding ambient pressure but including pressure in the wall exerted by more external elements of the wall. The stresses in the other class of equations are fiber-pulling forces per unit normal area, that is, total forces per unit normal area excluding all pressure. The validity of stress equations can be tested at least three ways: 1) Do they predict that the pressure inside a small chamber nested in a larger chamber would be the sum of transmural pressures of the two chambers? 2) Do they satisfy the expectation from Laplace's law that a sphere with a given circular stress and thickness/radius ratio would exert twice the pressure of a cylinder with the same circular stress and thickness/radius ratio? 3) Do they predict that the ratio of principle stresses depends on chamber shape but not on wall/cavity ratio, with the circular/longitudinal stress ratio of a cylinder being 2 and that of a prolate spheroid being between 1 and 2? Stress equations of the first class fail all of these tests by large margins, whereas those of the second class pass all of these tests exactly.(ABSTRACT TRUNCATED AT 250 WORDS)

An increase in early rates of oleate uptake, which reflected fatty acid (FA) entry into the cells, was apparent 2-3 days after confluence of differentiating BFC-1 preadipocytes. The increase was measured in cells kept without glucose and with arsenate, where >95% of intracellular radioactivity was recovered as free unesterified oleate. Uptake of retinoic acid, a molecule structurally similar to long-chain FA, remained unaltered during cell differentiation. Increase in oleate transport was related to increase in transport Vm.x (determined under arsenate treatment) from 0.2 to 2 nmol/min per 106 cells, whereas Km remained unchanged (2 x 10-7 M).Oleate transport was maximal at about day 6 after cell confluence (day 0), as FA metabolism (incorporation into lipids) began to gradually increase. The increase in transport preceded induction of mRNAs for both cytosolic FA-binding protein, which appeared at day 6, and for the FA synthase, which appeared at day 10. Data indicated that increases in activities of FA transport and of lipoprotein lipase, early during cell differentiation, favored increased availability of exogenous FA at a stage when endogenous FA synthesis is limited. This result would promote FA esterification and lipid deposition by supplying a rate-limiting substrate. Furthermore, oleate addition to BFC-1 preadipocytes at confluence potentiated the effect of dexamethasone in inducing mRNA for cytosolic FA-binding protein. In adipocytes, FA from exogenous or endogenous sources was necessary to maintain levels of cytosolic FAbinding protein mRNA. Thus, the increase in FA availability might contribute to, or modulate, induction of proteins necessary for preadipocyte differentiation.Fatty acid (FA) permeation across the plasma membrane of adipocytes has been shown to be carrier mediated with characteristics of facilitated diffusion (1-3). Multiple lines of evidence suggested that FA transport might be important in regulating FA metabolism (4, 5). To gain more insight into the physiological significance of the transport system we studied oleate uptake and metabolism in cultured adipocytes. Adipose cells in culture offer an ideal system where transport and metabolism of FA can be related as the cell differentiates and acquires the adipose phenotype.BFC-1 cells, established from mouse brown fat tissue, express many of the characteristics of other adipose cell lines like 3T3 Li and 3T3 F442A. They show a high rate of differentiation with temporally well-defined stages (6). We have previously shown that BFC-1 adipocytes when compared with preadipocytes exhibited an increased rate of fatty acid uptake necessary to accommodate their higher rate of FA metabolism (7). Whether the increase in FA uptake reflected membrane or metabolic events and whether it preceded or followed acquisition of other markers of differentiation remained uncertain. Such information will help determine whether increased substrate availability is involved in the differentiation process. In this study we have characterized uptake of [3H]...