The development of the early atrioventricular conduction system in the embryonic heart

Recent electrophysiological evidence indicates that periodic spontaneous depolarizations occur in the primordial heart of the bird (and presumably mammal) even before the myocardial cells can contract, and these are initiated in the primordial sinoatrial region. As contractions are generated, these then establish a peristaltic wave. From that time on, during ontogenesis, the contractile sequence follows a regular pattern of development. As chambers form they contract sequentially in the direction of blood flow, even though, in the twisted configuration, myocardial continuities suggest the possibility of short-circuiting the electrical conduction pathways from atrium to bulbus. This implies that, even at these early stages, the electrical properties of the myocardium are not isotropic, and that specialized conduction pathways must exist. To the present time, electrophysiological techniques have limited the direct evidence that can be obtained on these delicate electrically specialized pathways. However, microscopical techniques have permitted studies on the morphological development of the tissue and of the cells in the various regions of the myocardium. The present paper traces the development of cell morphology in these regions, including the development of structural nodes and proximal ventricular fibre pathways, and from these observations, the manner in which the electrical conduction pathways are believed to develop is suggested.     

New C-nucleoside analogs by dehydration of 1-benzyl-4,5,6,7-tetrahydro-6,6-dimethyl-2-(d-galacto-pentitol-1-yl)-indol-4-one

The reaction between 2-(benzylamino)-2-deoxy-d-glycero-l-gluco-heptose and 5,5-dimethyl-1,3-cyclohexanedione yields 1-benzyl-4,5,6,7-tetrahydro-6,6-dimethyl-2-(d-galacto-pentitol-1-yl)-indol-4-one (2). Acid-catalyzed, intramolecular dehydration of 2 under kinetically controlled conditions gives 1-benzyl-4,5,6,7-tetrahydro-2-α-d-lyxofuranosyl-6,6-dimethylindol-4-one; the anomeric configuration of this compound is only suggested. When the dehydration reaction is conducted under thermodynamically controlled conditions, it produces a 1:1 mixture of the α- and β-d-lyxopyranosyl compounds. The structures of the new compounds were elucidated by chemical and physical methods.     

Bleomycin stimulates both membrane (Na+-K+) ATPase and electrogenic (Na+-K+) pump and partially removes the inhibition by vanadium ions

Bleomycin 2 X 10(-6) and 6 X 10(-6) mol.1(-1) increased the activity of specific (Na+-K+) ATPase of the rat brain microsomes. It also stimulated the electrogenic (Na+-K+) pump in intact skeletal muscle cells. The blocking effect of vanadyl (+4V) on membrane (Na+-K+) ATPase was eliminated completely by the drug, but the action of vanadate (+5V) was counteracted only partially. Electron paramagnetic resonance spectra revealed the formation of a +4V - bleomycin complex which is still able to activate the (Na+-K+) ATPase.     

Fine needle aspiration cytology of thymic tumors

Cytologic material was reviewed from 23 mediastinal tumors clinically suspected as thymomas. The thymomas had a characteristic biphasic cell pattern in material obtained by fine needle aspiration biopsy that was easy to recognize and possible to differentiate from carcinoid tumors, malignant lymphomas and oat-cell carcinomas.     

A 1H-NMR longitudinal relaxation study of the interaction between cytochrome c and cytochrome c oxidase

The interaction between the oxidized forms of cytochrome c and cytochrome c oxidase (EC 1.9.3.1) has been investigated by ¹H-NMR longitudinal relaxation measurements. It is found that relaxation of methyl groups on the heme ring of cytochrome c markedly deviates from a simple exponential behavior in the presence of small amounts of cytochrome oxidase. A comparison with the relaxation behavior of cytochrome c modified by 4-carboxy-3,5-dinitrophenyl at Lys-13 shows that the oxidase induces a conformation in native cytochrome c that is closely related to that of the derivative. It is suggested that this change in conformation consists of a rupture of the salt bridge between Lys-13 and Glu-90 and a concomitant perturbation of the methionine ligand.     

Spectroscopic properties of protochlorophyll forms in Triton X-100 detergent micelles

Protochlorophyll (PChl) forms were performed in Triton X-100 detergent micelles. The concentration of Triton X-100 was 7·10^?4 M (above the critical micellar concentration); the concentration of PChl varied between 1.6·10^?5 and 1.8·10^?4 M. Absorption, fluorescence and circular dichroism (CD) spectra were registered. The absorption spectra were resolved into Gaussian components by computer analysis. PChl forms with absorption bands at 632–634, 638, 652–654, 663–664, 668 and 676 nm and with fluorescence emission bands at 634–636, 640–644, 652–655, 677–678, 686 and 694–696 nm were observed in micellar solutions of different PChl concentrations. The CD spectra showed a strong dependence on the concentration of PChl: positive CD signals or positive Cotton effects were observed in the vicinity of 650 nm. The intensity of these signals increased in parallel with increasing concentration of PChl. No CD signals were found in the region of the longer wavelength absorption bands. These data show that the PChl exists in many different forms in this system, and the spectroscopic properties of these forms are determined by different molecular interactions viz., interactions of PChl with Triton X-100 or water molecules and/or by the aggregation of PChl.     

Proteoheparan sulfate from human skin fibroblasts. Evidence for self-interaction via the heparan sulfate side chains

We have studied the affinity between fibroblast proteoheparan sulfate (medium- and cell surface-derived species) and heparan sulfate-agaroses by affinity chromatography. The evidence for an interaction between the heparan sulfate side chains of the proteoglycans and the immobilized heparan sulfate are as follows: (a) the individual side chains released from the proteoglycan by papain bind to the affinity matrix, (b) the bound proteoglycans are desorbed by a solution of cognate heparan sulfate chains, and (c) the core protein obtained by heparan sulfate-lyase digestion of the proteoglycan does not bind to the affinity matrix. The proteoglycans interact only with one subtype of heparan sulfate. The binding of free heparan sulfate chains to the affinity matrix is completely abolished by heparan sulfate oligosaccharides provided they are composed of both iduronate- and glucuronate-containing disaccharide sequences.     

Identification of lactaldehyde dehydrogenase and glycolaldehyde dehydrogenase as functions of the same protein in Escherichia coli

Lactaldehyde dehydrogenase is an enzyme involved in the aerobic metabolism of fucose in wild type Escherichia coli, and glycolaldehyde dehydrogenase is an enzyme involved in the metabolism of ethylene glycol in mutant cells able to utilize this glycol. Both enzyme sources display oxidative activity on either substrate with a constant ratio between these activities. We have found that both enzymatic activities present the same electrophoretic mobility when crude extracts were electrophoresed in polyacrylamide gels and the gels stained for enzyme activities. Furthermore, both enzymatic activities co-chromatograph in a DEAE-Sephadex column. If lactaldehyde dehydrogenase of wild type cells is purified near homogeneity and the purification procedure is screened for both aldehydes as substrates, only one enzyme is apparent, giving again a constant ratio between lactaldehyde and glycolaldehyde dehydrogenase activities. Genetic evidence of the fact that both activities are functions of the same protein is provided by the observation that mutation to thermosensitivity for the production of lactaldehyde dehydrogenase affected in the same way the production of glycolaldehyde dehydrogenase. Glycolaldehyde dehydrogenase from mutant cells is purified in a procedure coincident with the lactaldehyde dehydrogenase purification, yielding a single enzyme electrophoretically indistinguishable from the purified lactaldehyde dehydrogenase. Peptide mapping of the purified preparation after digestion with chymotrypsin or Staphylococcus aureus protease V8 gives an indistinguishable band pattern between both enzymes.     

Interaction of medroxyprogesterone acetate with cytosol androgen receptors in the rat hypothalamus and pituitary

The binding of medroxyprogesterone acetate (MPA) with cytosol androgen receptors from rat pituitary and hypothalamus was studied. The pituitary and hypothalamic cytosol androgen receptors from adult castrated female rats were in vitro labeled using 3H natural (testosterone (T) and 5 alpha-dihydrotestosterone (DHT] and [3H]synthetic (methyltrienolone) androgens as radioligands. The [3H]androgen-receptor complexes sedimented with a coefficient of 8S in linear sucrose gradients. When incubated with an excess of radioinert MPA, specific binding was abolished indicating interaction of MPA with androgen receptors. Furthermore specific [3H]MPA-androgen cytosol receptor complexes could be identified in these neuroendocrine tissues when a post-gradient receptor labeling technique was used in the absence or presence of radioinert MPA, DHT, and triamcinolone acetonide. A study of binding kinetics disclosed that the equilibrium dissociation constant and saturation binding capacity for the MPA binder, were similar to those exhibited by DHT binding to androgen receptors in both studied tissues under identical experimental conditions. The overall results were interpreted as demonstrating that MPA interacts with cytosol steroid receptors other than those of progesterone in the rat hypothalamus and anterior pituitary. The data are consistent with MPA binding to androgen receptors.