A B S T R A C T The stimulatory effect of low concentrations ofouabain on the Na-K pump in isolated guinea pig left atria was studied in vitro by assessing active transport of the K+ analog Rb+. Active transport of Rb+ was stimulated 20+8% (SEM, P < 0.05) above control values by 3 nM ouabain, but was inhibited by concentrations >10 nM. Preincubation with the f-adrenergic antagonist propranolol (1 ,uM) completely blocked stimulation of active transport of Rb+ by 3 nM ouabain. Norepinephrine, 10 nM, increased Rb+ active transport 29±10% (P < 0.02) above control values. The /8-adrenergic agonist 1-isoproterenol, 10 nM, increased active transport of Rb+ by 33±10% (P < 0.01) above control levels. This stimulatory effect was abolished if tissues were first exposed to propranolol. Tyramine (0.1 ,uM), a stimulator of endogenous catecholamine release, increased active transport of Rb+ 26±12% (P < 0.05) above control values. Rb+ active transport was not significantly changed when left atrial tissues were incubated with a-adrenergic agonists or antagonists. Ouabain stimulation of Rb+ active transport was prevented by in vivo depletion of myocardial endogenous catecholamines by either reserpine or 6-hydroxydopamine. These findings indicated that in myocardial tissue, Na-K pump stimulation by low concentrations of ouabain is mediated at least in part through j8-adrenergic effects of endogenous catecholamines.
Several years ago Hall and Elting pointed out that certain raw cottons which had been subjected to the action of fungi in the field or immediately after harvesting suffered a deterioration in cotton quality characteristics upon storage in bale form. Such cotton was termed by them to be "cavitomic." This deterioration was most manifest in a reduction of processing efficiency and a lowering of yarn quality. Certain chemical tests (pH and reducible sugars) were established as methods to detect cavitomic cotton.
A modified method for evaluating the distribution of pore spaces within a textile fabric, based on the principle outlined in the preceding paper in this series [1], is described. Data are reported for 14 tight fabrics, 6 of which had been treated with a water-repellent finish. The porosities of these fabrics are compared with the results of airand hydrostatic-permeability measurements.
The structural reversals in cotton fibers are a preferred location of break when the fiber is ruptured in tension. With the aid of a polarizing microscope, observations were made of the fraction of fibers breaking at the reversals under various conditions of moisture content, specimen length, and chemical treatment. It is concluded that the cellulose in the region of the reversals is more highly crystalline than the cellulose between the reversals. The cause for breakage at the reversals is then explained on the basis of internal stresses at these points which cause the fiber to tear apart when tension is applied. The weak places between reversals which give rise to fiber rupture are believed to be at structural defects or thin places. The mean breaking stresses for fibers breaking at the reversals vary significantly from those for fibers breaking between reversals for some varieties of cotton. The distributions of weak-spot location and strength for reversals and structural defects are discussed for three varieties.
A serious problem in single-fiber testing is the preparation of a homogeneous sample from which fibers may be selected in a random manner. Mechanical blenders, of the type developed for cotton by the U. S. Department of Agriculture, greatly improve the homogeneity of a bulk fiber sample. In the present work tests were made to show what changes in single-fiber proper ties result from the mechanical action of such a blender. Relatively small changes in mechanical behavior of the cotton fibers were observed as a result of blending. With the conventional three passes through the blender a small decrease in break ing load (less than 10%) was found, with corresponding changes in breaking stress and energy to break. A reduction of fiber crimp with a slight increase in fiber length by the fiber array method was also noted.
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