Aminophylline increases submaximum power but not intrinsic velocity of shortening of frog muscle.

We hypothesized that methylxanthines, such as aminophylline, increase the power developed by submaximally activated frog skeletal muscles by increasing the force developed at any given velocity of shortening. Frog semitendinosus muscles were excised and tested at 20 degrees C in oxygenated control and aminophylline Ringer solutions. Force-velocity relationships were determined and power was calculated from muscles stimulated at frequencies of 80 and 300 Hz. The 300-Hz frequency of stimulation produced a maximum rate of force development. In 50 and 500 microM aminophylline, twitch force increased by 25 +/- 12 and 75 +/- 13%, respectively. Aminophylline did not affect maximum isometric force generation or the shortening velocity at any relative load. At 80-Hz stimulation and in the presence of 500 microM aminophylline, power increased by an average of 11% at 10 of 14 relative loads. At maximum frequencies of stimulation, aminophylline had no effect on any measured parameter. We conclude that aminophylline increases the power developed by submaximally activated frog muscles through an increase in the force generated particularly at the lower velocities of shortening.     

Nyssa talamancana (Cornaceae), an addition to the remanant Laurasian Tertiary flora of southern Central America

A new species,Nyssa talamancana, with fruits larger than those of any other, either living or fossil, is described from Costa Rica and Panama. In size, number of germination valves, and surface-sculpturing, its endocarps resemble those of the fossil assemblage more than those of the other living species. The occurrence of this distinctive new member of a definitely Laurasian family, in association with other endemic or nearly endemic Laurasian taxa, at wet mid-elevations lends credence to the idea that these forests harbor remnants of the really ancient flora of southern Central America.     

Plasminogen activator: The major secreted neutral protease of cultured skeletal muscle cells

Clonal mouse skeletal muscle cells which differentiate in culture and from synpases with neuronal cells were found to secrete high levels of protease activity as measured with an ¹²⁵I-fibrin assay. The secreted proteolytic activity was more than 90% dependent upon the presence of plasminogen in the medium, and had a pH optimum at 7 to 8. This activity was not inhibited by n-ethylmaleimide, pepstatin, EDTA, or EGTA. At millimolar concentrations, greater than 90% inhibition was obtained with either soybean typsin inhibitor, epsilon aminocaproic acid, Trasylol, or leupeptin. Almost complete inhibition occured with 1 mM diisopropylfluorophosphate suggesting the presence of a serine residue at the catalytic site. In contrast to the high levels of secreted activity, a lower steady-state level of cell-associated protease activity was detected in cell lysates. The high level of plasminogen activator secreted into the medium of cultured muscle cells suggests a role for such extracellular protease activity in myogenesis during development and remodeling following muscle injury. Such information may be useful in understanding the initial degeneration of neuromusclar contacts in experimental and pathologic denervation.     

Evidence for two genetic complementation groups in pyruvate carboxylase-deficient human fibroblast cell lines

We have examined genetic complementation in pyruvate carboxylase deficiency by comparing the enzyme activity in polyethylene glycol-induced heterokaryons with that in unfused mixtures of fibroblasts from three affected children. Complementation, manifested as a three- to sevenfold increase in pyruvate carboxylase activity, was observed in fusions between a biotin-responsive multiple carboxylase (pyruvate carboxylase, propionyl CoA carboxylase, and -methylcrotonyl CoA carboxylase) deficient fibroblast line and two other lines deficient only in pyruvate carboxylase activity. Kinetic analysis of complementing pyruvate carboxylase deficient lines, measured by the rate of restoration of enzyme activity as a function of time, revealed that maximum restoration was achieved within 10–24 hr after fusion. This profile is similar to those observed for fusions between the multiple carboxylase deficient line and two lines deficient in propionyl CoA carboxylase activity that are known to represent different gene mutations. Although the patients with pyruvate carboxylase deficiency had similar clinical findings, our studies indicate that pyruvate carboxylase deficiency is genetically heterogeneous, with at least two distinct, probably intergenic, complementation groups.This work was supported by an NIH research grant (AM 25675) and an A. D. Williams research grant (6-48360). B. Wolf is the recipient of an NIH Research Career Development Award (AM 00677) and is aided by a Basil O'Connor Starter Research Grant from The National Foundation-March of Dimes (5-263). G. Feldman is the recipient of an NIH predoctoral training grant (GM 07492). This article is No. 100 from the Department of Human Genetics at the Medical College of Virginia.     

Uterine prostaglandin levels following stimulation of the decidual cell reaction: Effects of indomethacin and tranylcypromine

Prostaglandin E (PGE) and F (PGF) levels were measured in mouse uteri at various times after either trauma (hemostat crushing) or oil stimulation of the decidual cell reaction (DCR). The oil induced DCR led to an early increase (within 5 min) in both PGE and PGF levels. Both returned to baseline by 1 h after stimulation. A second peak in PGF levels was observed at 120 min after oil stimulation. This study demonstrates a distinct difference between the pattern of PGE and PGF changes in the uterus following oil stimulation of the DCR. Indomethacin pretreatment completely blocked the oil stimulated DCR as well as all prostaglandin increases following either stimulus. The trauma stimulated DCR was not completely blocked by indomethacin pretreatment.Pretreatment with tranylcypromine, an inhibitor of prostacyclin biosynthesis, did not block the prostaglandin E and F increases, but did block the oil stimulated DCR. These findings suggest that prostacyclin may be an early mediator of the DCR.     

Lysinonorleucine cross-link formation in alpha amino heptenoic acid-substituted peptide derivatives

Studies on the cross-linking of a tripeptide (t-butyloxycarbonyl-L -alanyl-D ,L -2-amino-6-heptenoyl-L -alanine methyl ester) have shown that it is possible to form specific cross-links in good yields through Schiff base formation of the ε amino group of lysine. The heptenoic acid residue has been ozonized to an aldehyde and condensed with the ε amino of lysine in the compounds alpha-t-butyloxycarbonyl-L -alanyl-L -lysine methyl ester and alpha-t-butyloxycarbonyl-L -lysine methyl ester to form the cross-link, lysinonorleucine. This compound has been stabilized by reduction with sodium borohydride and quantitated on the amino acid analyzer. This technique converts from 60 to 98% of the available aldehyde to lysinonorleucine.     

Perturbation of the chemotactic tumbling of bacteria

The bacterial sensing system has been studied on three levels. First, a quantitative method has been devised for measuring the “action spectrum” of the bacterium in response to a sudden addition of attractant. Second, a technique has been developed for the rapid isolation of mutants defective in the transmission part of the sensing system. Third, a study of the effects of light on the transmission system reveals two components, one which generates tumbling and another which inhibits it.