Carbonyldiphosphonate, a selective inhibitor of mammalian DNA polymerase delta

Twenty-three pyrophosphate analogues were screened as inhibitors of proliferating cell nuclear antigen independent DNA polymerase delta (pol delta) derived from calf thymus. Carbonyldiphosphonate (COMDP), also known as alpha-oxomethylenediphosphonate, inhibited pol delta with a potency (Ki = 1.8 microM) 20 times greater than that displayed for DNA polymerase alpha (pol alpha) derived from the same tissue. Characterization of the mechanism of inhibition of pol delta indicated that COMDP competed with the dNTP specified by the template and was not competitive with the template-primer. In the case of pol alpha, COMDP did not compete with either the dNTP or the polynucleotide substrate. COMDP inhibited the 3'----5' exonuclease activity of pol delta weakly, displaying an IC50 greater than 1 mM.     

Optimisation of total urinary aldosterone estimation: comparison with other laboratory methods for assessment of mineralocorticoid status

We have demonstrated that conventional methods for measuring total urinary aldosterone (TUA) may markedly and inconsistently underestimate aldosterone output, since under the conditions usually employed (pH 1.0), the hydrolysis of aldosterone conjugates in urine is incomplete. The use of more acidic hydrolysis conditions (pH 0.2) overcomes this problem. However free aldosterone may be damaged at this pH. Therefore to accurately measure TUA output, it is necessary to isolate the undamaged aldosterone chromatographically and to correct for procedural losses based on the recovery of aldosterone tracer added to the urine prior to hydrolysis. We compared a number of laboratory estimates of aldosterone status (including urinary free aldosterone) with the 24-h urinary sodium output in normal subjects, since this provides a good bioassay of aldosterone. Sodium output correlated best with "optimised" 24 h TUA, i.e. hydrolysed at pH 0.2, (r = -0.589, P less than 0.001), and with plasma aldosterone (r = -0.504, P less than 0.005). Both aldosterone in random urine specimens and plasma renin activity correlated poorly with 24-h sodium output. Therefore, while the measurement of optimised TUA excretion provides the best index of aldosterone activity, assay of aldosterone in random specimens of plasma, which is more convenient for patient and laboratory, may be adequate for many clinical purposes.     

Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells

Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction.     

Cytochemical changes in hepatocytes of rats with endotoxemia or sepsis: localization of fibronectin, calcium, and enzymes

Bacterial lipopolysaccharide (LPS) is known to be implicated in the pathogenesis of endotoxemia and septic shock. The liver is the first vital organ to exhibit pathological alterations in shock. The present studies include immunoelectron microscopic localization of tissue fibronectin and cytochemical localization of calcium and enzymes in hepatocytes of animals with LPS-induced endotoxemia or cecal ligation-induced septic shock. The results showed increased staining of fibronectin in the basal (perisinusoidal) surfaces and in the cisternae of rough endoplasmic reticulum and the Golgi complex of hepatocytes in rats with endotoxemia or septic shock. Intracellular calcium content was significantly increased in the LPS-treated or septic rats. Calcium pyroantimonate precipitate was deposited predominantly on the outer surfaces of the RER of hepatocytes. In addition, diminution or depletion of glycogen, reduction of catalase-containing peroxisomes, increase of G-6-Pase activity, and depletion of cytochrome c oxidase in many mitochondria were also observed in hepatocytes of experimental animals. The overall results suggest that LPS stimulates: (a) hepatic synthesis and secretion of fibronectin; (b) uptake of calcium by hepatocytes; and (c) G-6-Pase activity. LPS treatment also leads to reduced numbers of peroxisomes and depletion of cytochrome c oxidase.     

Identical distribution of fluorescently labeled brain and muscle actins in living cardiac fibroblasts and myocytes

We have investigated whether living muscle and nonmuscle cells can discriminate between microinjected muscle and nonmuscle actins. Muscle actin purified from rabbit back and leg muscles and labeled with fluorescein isothiocyanate, and nonmuscle actin purified from lamb brain and labeled with lissamine rhodamine B sulfonyl chloride, were co-injected into chick embryonic cardiac myocytes and fibroblasts. When fluorescence images of the two actins were compared using filter sets selective for either fluorescein isothiocyanate or lissamine rhodamine B sulfonyl chloride, essentially identical patterns of distribution were detected in both muscle and nonmuscle cells. In particular, we found no structure that, at this level of resolution, shows preferential binding of muscle or nonmuscle actin. In fibroblasts, both actins are associated primarily with stress fibers and ruffles. In myocytes, both actins are localized in sarcomeres. In addition, the distribution of structures containing microinjected actins is similar to that of structure containing endogenous F-actin, as revealed by staining with fluorescent phalloidin or phallacidin. Our results suggest that, at least under these experimental conditions, actin-binding sites in muscle and nonmuscle cells do not discriminate among different forms of actins.