Computer-aided interactive three-dimensional reconstruction of the embryonic human heart

Despite the fact that development of the human embryo heart is of considerable clinical importance, there is still disagreement over the process and the timing of events. It is likely that some of the conflicting accounts may have arisen from difficulties in describing and visualising 3-dimensional structures from 2-dimensional sections. To help overcome this problem and to improve our understanding of the development of the heart, we have devised techniques for the production of interactive 3D models reconstructed from serial histological sections of human embryos. Our method uses commercial software designed for the creation of 3D models and virtual reality environments. The ability to construct interactive visual images which both illustrate and communicate complex 3D information contributes to our understanding of the complex developmental changes occurring in embryogenesis.

Cartilaginous development of the human craniovertebral junction as visualised by a new three-dimensional computer reconstruction technique

Serial transverse histological sections of the human craniovertebral junction (CVJ) of 4 normal human embryos (aged 45 to 58 d) and of a fetus (77 d) were used to create 3-dimensional computer models of the CVJ. The main components modelled included the chondrified basioccipital, atlas and axis, notochord, the vertebrobasilar complex and the spinal cord. Chondrification of the component parts of CVJ had already begun at 45 d (Stage 18). The odontoid process appeared to develop from a short eminence of the axis forming a third occipital condyle with the caudal end of the basioccipital. The cartilaginous anterior arch of C1 appeared at 50-53 d (Stages 20-21). Neural arches of C1 and C2 showed gradual closure, but there was still a wide posterior spina bifida in the oldest reconstructed specimen (77 d fetus). The position of the notochord was constant throughout. The normal course of the vertebral arteries was already established and the chondrified vertebral foramina showed progressive closure. The findings confirm that the odontoid process is not derived solely from the centrum of C1 and that there is a 'natural basilar invagination' of C2 during normal embryonic development. On the basis of the observed shape and developmental pattern of structures of the cartilaginous human CVJ, we suggest that certain pathologies are likely to originate during the chondrification phase of development.

The study of early human embryos using interactive 3-dimensional computer reconstructions

Tracings of serial histological sections from 4 human embryos at different Carnegie stages were used to create 3-dimensional (3D) computer models of the developing heart. The models were constructed using commercially available software developed for graphic design and the production of computer generated virtual reality environments. They are available as interactive objects which can be downloaded via the World Wide Web. This simple method of 3D reconstruction offers significant advantages for understanding important events in morphological sciences.

World Wide Web access to the British Universities Human Embryo Database

The British Universities Human Embryo Database has been created by merging information from the Walmsley Collection of Human Embryos at the School of Biological and Medical Sciences, University of St Andrews and from the Boyd Collection of Human Embryos at the Department of Anatomy, University of Cambridge. The database has been made available electronically on the Internet and World Wide Web browsers can be used to implement interactive access to the information stored in the British Universities Human Embryo Database. The database can, therefore, be accessed and searched from remote sites and specific embryos can be identified in terms of their location, age, developmental stage, plane of section, staining technique, and other parameters. It is intended to add information from other similar collections in the UK as it becomes available.

The World-Wide Web: an interface between research and teaching in bioinformatics

The rapid expansion occurring in World-Wide Web activity is beginning to make the concepts of 'global hypermedia' and 'universal document readership realistic objectives of the new revolution in information technology. One consequence of this increase in usage is that educators and students are becoming more aware of the diversity of the knowledge base which can be accessed via the Internet. Although computerised databases and information services have long played a key role in bioinformatics these same resources can also be used to provide core materials for teaching and learning. The large datasets and archives that have been compiled for biomedical research can be enhanced with the addition of a variety of multimedia elements (images, digital videos, animation etc.). The use of this digitally stored information in structured and self-directed learning environments is likely to increase as activity across World-Wide Web increases.

Incorporation of inositol into the phosphoinositides of lymphoblastoid cell lines established from bipolar manic-depressive patients

Lymphoblastoid cell lines established from patients suffering from bipolar manic-depressive psychosis or from a control group have been used to study the metabolism of the polyphosphoinositides in these cells. Cells were incubated for up to 6 h in [3H]inositol and the extent of inositol incorporation into the mono-, di- and triphosphoinositides was measured after extracting the water- and lipid-soluble inositol-containing pools. Although both the uptake of inositol and the 'free' intracellular inositol pool sizes were similar in the two cell groups, the incorporation of [3H]inositol into the phosphoinositides of the cells derived from bipolar manic-depressives was significantly less (by around 50-60%) than that which occurred in the control cells.

Characterisation of atrial natriuretic peptide receptors in bovine ventricular sarcolemma

Analysis of [125I]-ANP binding data in an isolated bovine ventricular sarcolemmal membrane fraction revealed a single high affinity binding site (Kd approximately 5 x 10(-11) M). The ring deleted ANP analogue des [QSGLG]-ANP (4-23)-NH2 bound with a 1000-fold lower affinity indicating the absence of C-type receptors in this preparation. ANP stimulated guanylate cyclase activity by up to 2-fold with half-maximal activation at approximately 10(-9) M. Crosslinking [125I]-ANP to its receptor with disuccinimidyl suberate (DSS) revealed two radiolabelled bands of 120 kDa and 65 kDa on non-denaturing SDS-PAGE. Radioactive signals from both bands were lost by reducing the sample with beta-mercaptoethanol prior to electrophoresis, in which case a radioactive fragment of less than 5 kDa migrated with the dye front. These results suggest that the binding of ANP to both high and low molecular weight "receptor" proteins may be associated with the hydrolysis of the peptide.

Atrial natriuretic peptide receptors and activation of guanylate cyclase in rat cardiac sarcolemma

Two classes of atrial natriuretic peptide (ANP) receptors are present in purified sarcolemmal membrane fractions isolated from rat ventricle. Scatchard analysis using [125I]-ANP reveals high affinity (Kd approximately 10(-11) M) and low affinity (Kd approximately 10(-9) M) binding sites. Basal guanylate cyclase activities associated with these membrane fractions range from 3.2 +/- 1.3 pmol/min/mg protein in the presence of Mg2+ to 129 +/- 17 pmol/min/mg protein in the presence of Mn2+. Millimolar concentrations of adenosine triphosphate (ATP) potentiates Mg2+- but not Mn2+-supported activity. Binding of ANP to the low affinity site but not the high affinity site results in a maximum 2-fold activation of Mn2+- and up to 6-fold activation of Mg2+/ATP supported guanylate cyclase activities.

Cation transport in lymphoblastoid cell lines established from bipolar manic-depressive patients

Lymphoblastoid cell lines established from patients suffering from bipolar manic depression have been used to study the possible involvement of cation transport in the aetiology of this illness. No significant difference was found in the K+ fluxes mediated by the ouabain-sensitive sodium pump, the diuretic-sensitive cotransport system and the passive leak pathway of cell lines established from either control or bipolar subjects. The mean value for the specific binding of 3H-ouabain (sodium pump site number) was significantly higher in the bipolar group (approximately 30%) than in the control group.

Actions of atrial natriuretic peptide (ANP) on cyclic nucleotide concentrations and phosphatidylinositol turnover in ventricular myocytes

Atrial natriuretic peptide (ANP) stimulates cGMP production in isolated rabbit ventricular myocytes incubated in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine (1mM). Half maximal activation was found at 10(-8)M ANP. Cellular cGMP concentrations of around 0.6 pmol/10(6) cells were elevated 4-6 fold by ANP (10(-6)M), 3-4 fold by carbachol (1mM) and around 10 fold by sodium nitroprusside (1mM). ANP had no effect on basal or isoprenaline-stimulated cAMP concentrations or on basal or noradrenaline-stimulated turnover of phosphatidylinositol. From these results we conclude that ANP receptors, coupled to particulate guanylate cyclase, exist in cardiac ventricular muscle. This indicates that ANP may also have a physiological action on ventricular muscle contractility during volume expansion.

Role of passive potassium fluxes in cell volume regulation in cultured HeLa cells

Cultured HeLa cells behave as ideal osmometers when subjected to hyperosmolar media, and show no volume regulatory behavior. In hypoosmolar solutions, cell swelling is not as great as predicted, and this is due largely to a loss of intracellular KCl. In hyperosmolar solutions there is a stimulation of the ouabain-insensitive but loop diuretic-sensitive 86Rb+ (K+) pathway. Analysis of the K+, Na+ and Cl- dependency of this K+ flux pathway demonstrates that the increase is principally due to an increase in its maximal velocity (Vmax). The sensitivity of this pathway to diuretic inhibition is unchanged in hyperosmolar media. Diuretic-sensitive 86Rb+ (K+) efflux stimulated by hypertonicity shows no marked dependence on external K+. The K+ loss observed in hypoosmolar media is distinct from the K+ transport pathway stimulated by hyperosmolar media on the basis of its sensitivity to furosemide and anion dependence.

The effects of vanadate on rabbit ventricular muscle adenylate cyclase and sodium pump activities

Vanadate in the +5 oxidation state has been reported to have a positive inotropic action on cardiac ventricular muscle. We have investigated the biochemical actions of vanadate on ventricular muscle adenylate cyclase and sodium pump activities in both intact or disrupted cell systems in an attempt to elucidate the mechanism(s) responsible for the physiological response. Vanadate at concentrations up to 100 microM (Ka = 2 microM) stimulated adenylate cyclase activity in sarcolemmal membrane preparations or disrupted myocytes isolated from rabbit ventricular muscle by 2-3-fold. Increasing the vanadate concentrations above 100 microM resulted in a progressive inhibition of basal or hormone-stimulated adenylate cyclase activity (Ki = 5 mM) which was similar to that found by the reaction product, pyrophosphate (Ki = 0.5 mM). Both activation and inhibition by vanadate was fully reversible. Maximum activation of adenylate cyclase by vanadate and isoprenaline were not additive whereas maximum fluoride activation was decreased (18%) and the forskolin-stimulated response was slightly potentiated. Vanadate reversibly inhibited ouabain-sensitive p-nitrophenylphosphatase activity (Ki = 60 nM) in sarcolemmal membrane preparations and disrupted myocytes. Complete inactivation was found at 1 microM vanadate. Acute or chronic incubation of intact myocytes with vanadate at concentrations up to 0.5 mM had no measurable affect on ouabain-sensitive 86Rb influx or isobutylmethylxanthine, isoprenaline or forskolin-stimulated accumulation of intracellular cAMP concentration. Inhibition of 86Rb influx and cAMP accumulation was found at higher concentrations of vanadate; however, this accompanied the progressive decrease in cell viability as measured by the decrease in percentage of rod-shaped cells. It is concluded that vanadate, at concentrations which have been reported to induce a positive inotropic action on mammalian ventricular muscle, does not increase adenylate cyclase activity or inhibit the sodium pump activity in intact myocytes. These results show that caution must be applied when extrapolating the actions found with vanadate in broken cell systems to intact tissues.

An effect of piretanide upon the intracellular cation contents of cells subjected to partial chronic (Na-K) pump blockade by ouabain

Cultured cells have been used to study the contribution made by the ouabain-insensitive but diuretic (piretanide)-sensitive K transport system (so-called cotransport) to the maintenance of intracellular Na+ and K+ contents in normal cells and in cells whose Na-pump sites have been subjected to chronic partial inhibition. In cells which have normally directed gradients of Na+ and K+, chronic incubation in piretanide (10(-4) M) for up to 24 hr has no significant effect on the internal ion contents of HeLa (human carcinoma), MDCK (dog kidney epithelium) or BC3H1 (mouse smooth muscle) cell lines. This observation is consistent with the notion that when the intracellular ion contents are in a normal steady state the net driving force acting upon the diuretic-sensitive K transport (Na + K + Cl cotransport system) is zero or very close to zero. When cells are subjected to chronic partial inhibition of the sodium pump as a consequence of growth in sublethal concentrations of ouabain (10(-9)-3 X 10(-7) M), the number of functional Na-pump sites decreases, the intracellular Na+ content increases and the intracellular K+ decreases in a dose dependent manner. Under these conditions, inclusion of piretanide (10(-4) M) causes a significant retardation of Na+ gain and K+ loss from the cells. This response is of high molar affinity (EC50 = 3-4 X 10(-6) M) and can be obtained with the other loop diuretics, furosemide and bumetanide. The data presented are consistent with the idea that in cells subjected to chronic partial inhibition of the Na-pump, there is a piretanide-sensitive exchange of intracellular K+ for extracellular Na+. Such an effect of the cotransport system would not be predicted on the basis of a tightly coupled electroneutral cotransport of Na+, K+ and Cl- with a stoichiometry of 1Na:1K:2Cl. The data are discussed in relation to the possible role of putative circulating endogenous inhibitors of the Na-pump.

Biochemical and physiological adaptation to chronic propranolol treatment in the rat

The biochemical and physiological aspects of isoprenaline sensitivity in normotensive rats were examined during and after abrupt withdrawal of chronic propranolol treatment. Serum propranolol concentrations in rats chronically treated for one month (0.125% propranolol in drinking water: 75-100 mg/kg/day) ranged from 7 to 23 ng/ml. At the height of the blockade, rats showed a decreased responsiveness in vivo to isoprenaline-induced increase in heart rate and fall in blood pressure; the ED50 values for isoprenaline being increased some 20- and 4-fold respectively. There was a 180% increase in beta-receptor number in sarcolemmal membranes isolated from ventricular muscle of these animals, together with increased basal (290%), fluoride- (100%), forskolin- (80%) and isoprenaline-stimulated (125%) adenylate cyclase activity. Twenty-four hours after propranolol withdrawal, serum propranolol concentrations were reduced by over 95%. At this time rats exhibited increased chronotropic and blood pressure responses to i.v. isoprenaline, indicated by the reduced ED50 values (2-fold and 12-fold respectively compared to controls). In addition, cardiac sarcolemmal beta-receptor number and adenylate cyclase activities were still significantly elevated above those of controls; 35% increase in beta-receptor number and increases of 96, 26, 13 and 37% in basal, fluoride-, forskolin- and isoprenaline-stimulated adenylate cyclase activities respectively. Forty-eight hours after drug withdrawal serum propranolol concentrations were only just detectable at 0.5 +/- 0.1 ng/ml. Although sarcolemmal beta-receptor numbers were still elevated (23%) isoprenaline-stimulated adenylate cyclase activity had returned to control values. However, both the fluoride- and forskolin-stimulated enzyme activities were decreased below control values by 12 and 23% respectively, suggestive of a reduction in the catalytic capacity of the adenylate cyclase complex. In parallel with the reduction in beta-receptor number and adenylate cyclase activity, the chronotropic response to i.v. isoprenaline had also returned to control values. In contrast, the blood pressure response to i.v. isoprenaline was still elevated in these animals indicated by the 5-fold reduction in the ED50 value compared with control animals.

Effect of the serum concentration of the growth medium on the sodium pump site density of cultured HeLa cells

The density of sodium pump sites in the plasma membrane of cultured HeLa cells has been measured as a function of the serum concentration of the cell growth medium. Growth in media containing increased concentrations of serum (from 1 to 20% v/v) leads to an increase in sodium pump site numbers (as measured by the specific binding of [3H]ouabain) and pump activity (as measured by the ouabain-sensitive 86Rb influx). Time-course studies show that (1) new sodium pump sites first appear some 3-6 h after transfer to medium containing an elevated serum concentration and (2) the serum-mediated increase in new sodium pump sites is completely abolished by the protein synthesis inhibitors, cycloheximide and actinomycin D. These results suggest that de novo protein synthesis is required for the development of the serum response. Preliminary characterization of the serum factor responsible for initiating the synthesis of new sodium pump sites indicates that the activity is associated with a high molecular weight serum fraction (greater than 50000). The different types of interaction seen between the serum effect and other experimental manoeuvres which initiate the synthesis of new pump sites (growth in low-K+ medium, growth in Li+ medium and pre-treatment with exogenous ATP) suggest that there may be more than one pathway for the control of sodium pump site synthesis in cultured HeLa cells.

Calcium elevation in cultured heart cells: its role in cell injury

Inhibition of the Na+-K+ pump in cultured embryonic chick heart cells promotes the elevation of intracellular Ca2+ and is a useful manipulation to study the relationship between Ca2+ and myocardial cell injury. One hour of Na+-K+ pump inhibition resulted in a fourfold increase in cell Na+, a 50% decline in cell K+, and a 5- to 10-fold increase in cell Ca2+, 45% of which is mitochondrial. The degree of cell injury induced by Ca2+ loading was evaluated by monitoring the content of adenosine 5'-triphosphate (ATP) and the release of the intracellular enzyme lactate dehydrogenase (LDH). Under these conditions ATP content declined by 25-30% and LDH release increased from 1 to 1.4% of the total LDH. Furthermore, cells subjected to 1 h of Na+-K+ pump inhibition and returned to control solution for 5 h showed that Ca2+ decreased to near control levels and ATP content was restored. Although inhibition of Na+-K+ transport caused a large increase in cell Ca2+, neither Na+-K+ pump inhibition nor elevation in total cell Ca2+ per se resulted in irreversible myocardial cell injury.

Effect of ouabain upon diuretic-sensitive K+ transport in cultured cells. Evidence for separate modes of operation of the transporter

(1) Unidirectional K+ (86Rb) influx and efflux were measured in subconfluent layers of MDCK renal epithelial cells and HeLa carcinoma cells. (2) In both MDCK and HeLa cells, the furosemide-inhibitable and chloride-dependent component of K+ influx/efflux was stimulated 2-fold by a 30 min incubation in 1 . 10(-3) M ouabain. (3) Measurements of net K+ loss and Na+ gain in ouabain-treated cells at 1 h failed to show any diuretic sensitive component, confirming the exchange character of the diuretic-sensitive fluxes. (4) Prolonged incubations for 2.5 h in ouabain revealed a furosemide- and anion-dependent K+ (Cl-) outward net flux uncoupled from net Na+ movement. Net K+ (Cl-) outward flux was half-maximally inhibited by 2 microM furosemide. (5) After 2.5 h ouabain treatment, the anion and cation dependence of the diuretic-sensitive K+ influx/efflux were essentially unchanged when compared to untreated controls.

K+ transport in "tight' epithelial monolayers of MDCK cells

Bidirectional transepithelial K+ flux measurements across 'high-resistance' epithelial monolayers of MDCK cells grown upon millipore filters show no significant net K+ flux. Measurements of influx and efflux across the basal-lateral and apical cell membranes demonstrate that the apical membranes are effectively impermeable to K+. K+ influx across the basal-lateral cell membranes consists of an ouabain-sensitive component, an ouabain-insensitive component, an ouabain-insensitive but furosemide-sensitive component, and an ouabain- and furosemide-insensitive component. The action of furosemide upon K+ influx is independent of (Na+ - K+)-pump inhibition. The furosemide-sensitive component is markedly dependent upon the medium K+, Na+ and Cl- content. Acetate and nitrate are ineffective substitutes for Cl-, whereas Br- is partially effective. Partial Cl- replacement by NO3 gives a roughly linear increase in the furosemide-sensitive component. Na+ replacement by choline abolishes the furosemide-sensitive component, whereas Li+ is a partially effective replacement. Partial Na+ replacement by choline abolishes the furosemide-sensitive component, whereas Li+ is a partially effective replacement. Partial Na+ replacement with choline gives an apparent affinity of approximately 7 mM Na, whereas variation of the external K+ content gives an affinity of the furosemide-sensitive component of 1.0 mM. Furosemide inhibition is of high affinity (K1/2 = 3 micrometer). Piretanide, ethacrynic acid, and phloretin inhibit the same component of passive K+ influx as furosemide; amiloride, 4,-aminopyridine, and 2,4,6-triaminopyrimidine partially so. SITS was ineffective. Externally applied furosemide and Cl- replacement by NO3- inhibit K+ efflux across the basal-lateral membranes indicating that the furosemide-sensitive component consists primarily of K:K exchange.

Occurrence of passive furosemide-sensitive transmembrane potassium transport in cultured cells

Furosemide (1 x 10(-4) M) inhibits a proportion of the total passive (ouabain-insensitive) K+ influx into primary chick heart cell cultures (85%), BC3H1 cells (75%), MDCK cells (40%) and HeLa cells (57%). This action of furosemide upon K+ influx is independent of (Na+ + K+)-pump inhibition since the furosemide-sensitive component of the K+ influx is identical in the presence and absence of ouabain (1 x 10(-3) M). For HeLa cells the passive, furosemide-sensitive component of K+ influx is markedly dependent upon the external K+, Na+ and Cl- content. Acetate, iodide and nitrate are ineffective as substitutes for Cl-, whereas Br- is partially effective. Partial Cl- replacement by NO3- gave an apparent affinity of 100 mM [Cl]. Na+ replacement by choline+ abolishes the furosemide-sensitive component, whereas Li+ replacement reduces this component by 48%. Partial Na+ replacement by choline+ gives an apparent affinity of 25 mM [Na+]. Variation in the external K+ content gives an affinity for the furosemide-sensitive component of approx. 1.0 mM. Furosemide inhibition of the passive K+ influx is of high affinity, half-maximal inhibition being observed at 5 x 10(-6) M furosemide. Piretanide (1 x 10(-4) M) and phloretin (1 x 10(-4) M) inhibit the same component of passive K+ influx as furosemide; ethacrynic acid and amiloride (both 1 x 10(-4) M) partially so. The stilbene, SITS (1 x 10(-6) M), was ineffective as an inhibitor for the furosemide-sensitive component.

Down-regulation of the sodium pump following chronic exposure of HeLa cells and chick embryo heart cells to ouabain

1 HeLa cells and primary cultures of embryonic chick heart cells were grown in medium containing low concentrations of ouabain for 24 h. 2 Compared with normal cells, cells grown in ouabain have fewer free sodium pump sites, an increased intracellular sodium concentration and a decreased intracellular potassium concentration. The cells are able to maintain their intracellular ion contents because the remaining pump sites have an increased turnover rate. 3 When cells that have been chronically exposed to ouabain are returned to normal growth medium, the sodium pump site numbers increase; the recovery process begins within 6 to 8 h and is complete within 24 h. Recovery of pump site numbers is primarily dependent upon de novo protein synthesis since the protein synthesis inhibitor, cycloheximide, prevents recovery.

The effect of exogenous adenosine triphosphate on potassium movements in HeLa cells

The effect of exogenous adenosine triphosphate (ATP) on the potassium movements of cultured HeLa cells has been studied. The results obtained were consistent with the hypothesis that, in these cells, externally applied ATP activates a tightly coupled potassium-potassium (K-K) exchange mechanism. The response to ATP was characterized by a transient, 20-fold increase in both the potassium influx and potassium efflux. The tight coupling of the K-K exchange mechanism was confirmed by the results of several different types of experiment, all of which demonstrated the consistent matching of the ATP-stimulated fluxes. Two different strains of HeLa cells gave quantitatively different responses under similar experimental conditions. The reason for this difference was investigated and evidence was obtained which was consistent with the view that the membrane potential also influenced the HeLa cell K-K exchange mechanism.

Potassium permeability of embryonic avian heart cells in tissue culture

The relationship between the external potassium concentration ([K]o) and membrane permeability has been reexamined using a tissue-cultured preparation of embryonic chick heart cells in which diffusional limitations are minimal. The unidirectional K efflux and electrochemical gradients were determined as a function of [K]o, and the results showed that potassium permeability was constant within the range of 1-20 mM [K]o. Membrane potentials were obtained in K-free solutions and correlated with 42K efflux and intracellular ion content measurements under the same conditions. In contrast to preparations of the intact embryonic chick heart, 42K efflux does not decrease in K-free media. Simulations of tracer measurements at reduced [K]o from naturally occurring cardiac muscle indicate that the experimentally observed decrease in 42K efflux could result from diffusional limitations. This observation, when coupled with the experimental results, suggests that the effect of low [K]o on membrane permeability in homeothermic preparations of cardac muscle should be reevaluated.

The high molecular weight proteins released from cultured cells

Studies have been performed with the serum-free culture medium taken from several fibroblast monolayer culture lines. A high molecular weight protein fraction was separated from the concentrated medium by sucrose density gradient centrifugation. Polyacrylamide gel electrophoresis was used to assess the degree of purification obtained. In the electron microscope the negatively stained high molecular weight proteins were found to closely resemble the alpha2-macroglobulins. The suggestion that these proteins from cultured cells resemble the cylindrical protein complex isolated from mammalian erythrocyte ghosts is not supported by this study. The results are discussed in the light of the extensive literature now available on the electron microscopy of high molecular weight proteins.