Uptake,Transport and Storage of Cardenolides in Foxglove. Cardenolide Sinks and Occurrence of Cardenolides in the Sieve Tubes of Digitalis lanata1

Cardiac glycoside transport was investigated on the organ and whole plant level. Uptake experiments were carried out with shoot and root cultures of Digitalis lanata. In both systems primary cardenolides, i.e., those with a terminal glucose in their oligosaccharide side chain, were taken up against their concentration gradient, whereas the glucose-free secondary cardenolides were not. Active uptake of primary cardenolides was further evidenced by KCN inhibition of uptake. Using plantlets grown in vitro the long-distance transport of primary cardenolides from the leaves to the roots was demonstrated. Cardenolides were also detected in etiolated leaves, induced on plants with green leaves, which are supposed to be unable to synthezise cardenolides de novo, providing further evidence for long-distance transport. Several primary cardenolides were detected in the honeydew excreted by aphids fed on Digitalis lanata leaves, indicating that the phloem is a transporting tissue for cardenolides. On the other hand, the xylem sap obtained by applying the pressure-chamber technique was cardenolide-free. It was concluded that in Digitalis primary cardenolides serve as both the transport and the storage form of cardenolides. After their synthesis they are either stored in the vacuoles of the source tissue or loaded into the sieve tubes, from which they are unloaded at other sites where they are trapped in the vacuoles of the respective sink tissue.     

Early after-depolarisations induced by noradrenaline may be initiated by calcium released from sarcoplasmic reticulum

We investigated the effect of 10^–8 M noradrenaline (NA) on [Ca²⁺], and electrical activity of single myocytes of guinea-pig ventricular myocardium loaded with Indo 1-AM. Membrane potential was recorded by means of the patch electrode and patch amplifier set to the current clamp mode. Cells were stimulated at a rate of 30/min by 3 ms pulses of the current injected through the recording electrode. Superfusion of NA resulted in slight shortening of action potentials (APs), increase in rate of rise and amplitude of the respective Ca²⁺ transients, and appearance of secondary Ca²⁺ transients of two kinds: 1. appearing before repolarisation of AP and decay of the preceding Ca²⁺ transient were completed and 2. appearing between the APs. We named them early after-transients (EAT) and delayed after-transients (DAT), respectively. Without any additional intervention EATS caused some prolongation of APs duration and DATs resulted in subthreshold delayed after-depolarisations (DADS). When sarcolemmal K⁺ conductance was decreased by tetraethylammonium (TEA) in the patch electrode or 20 M BaCl₂ in the Tyrode solution, EATs initiated early after depolarizations (EADs) and DATs initiated suprathreshold DADs triggering full-sized APs. Superfusion of 30.0 mM Na⁺ (replaced with LiCl) resulted in reduction of AP duration by -70% and appearance of DATs. Also, the frequent multiple oscillations of Ca ²⁺ concentration were often observed. Neither DATs nor the oscillations had any affect on electrical activity of the cells. Their electrogenicity could not be increased by TEA or 20.0 M Ba²⁺. EATs and DATs and their respective EADs and DADs could not be initiated by NA or low Na⁺ superfusion in the cells pretreated with 2 × 10^–7 M thapsigargin, a selective blocker of Ca²⁺-ATPase of sarcoplasmic reticulum (SR). We conclude that in contrast to the current hypothesis, EADs can be initiated by Ca²⁺ released early in the cardiac cycle from the overloaded SR, and that electrogenicity of both types of Ca²⁺ oscillations critically depends on the sarcolemmal K⁺ conductance.     

Testicular main ducts and spermatic ducts in some cyprinid fishes I. Morphology, fine structure and histochemistry

Alburnus alburnus, Leuciscus cephalus and Vimba vimba efferent duct systems of the male gonads consist of testicular main ducts and spermatic ducts. These have similar histological, fine structural and (enzyme–) histochemical characteristics and function in (1) storage and (2) nutrition of spermatozoa, (3) synthesis of steroid glucuronides, (4) secretion of proteins and enzymes (5) formation of an ionic gradient in the seminal fluid and (6) they have auto– and heterophagocytotic activities. Therefore testicular main ducts and spermatic ducts are important in the formation of the seminal fluid.     

Contact allergy to a subcutaneous implantable cardiac defibrillator – A rare problem with a golden solution

Contact allergy to implantable cardiac defibrillators (ICD) is an uncommon and underdiagnosed complication. We report a case of a 20-years-old man patient that was resuscitated from sudden cardiac death. Workup imaging study was unremarkable, but genetic testing identified a mutation in the KCNH2 gene of uncertain significance. The patient underwent a subcutaneous implantable cardiac defibrillator (S-ICD) implantation, with no complications. The patient suffered two hospital re-admissions due to a device-related inflammatory reaction, leading to two device re-implantations. At the first time, it was considered a bacterial infection and the S-ICD was replaced by an endovascular device. At the second time, a tissue-device interaction, with hypersensitivity reaction and device rejection was suspected. The skin patch-tests were inconclusive, but it was decided to implant a custom-made gold-coated endovascular ICD. Indeed, the tendency is an initial misdiagnosis as an infection and a high clinical suspicion is essential to an early diagnosis.     

IN VIVO EFFECTS OF CARDIOTROPHIN-1

Cardiotrophin-1 (CT-1) is a recently discovered cytokine that was isolated based on its ability to induce cardiac myocyte hypertrophy in vitro. In this study, the effects of chronic administration of CT-1 to mice (0.5 or 2 μg by intraperitoneal injection, twice a day for 14 days) were determined. A dose-dependent increase in both the heart weight and ventricular weight to body ratios was observed in the treated groups. The body weights of the animals were unaffected. These results indicate that CT-1 can induce cardiac hypertrophy in vivo. CT-1 was not specific for the heart, however. It stimulated the growth of the liver, kidney, and spleen, and caused atrophy of the thymus. CT-1 administration also increased the platelet counts by 70%, with no change in mean platelet volume. Red blood cell counts were increased in the treated animals, and there was a concomitant increase in haemoglobin concentration. Thus, CT-1 has a broad spectrum of biological activities in vivo. This observation is consistent with previous in-vitro findings showing that the mRNA for CT-1 is expressed in several tissues, and that CT-1 can function through binding to the leukaemia inhibitory factor (LIF) receptor and signalling through the gp130 pathway.     

Prevalence and upper limit of cardiac hypertrophy in professional cyclists

The term athlete's heart refers to an increased left ventricular mass. Few studies have assessed the prevalence and normal upper limit of cardiac hypertrophy in highly trained cyclists and this was the aim of this study. A group of 40 professional road cyclists [mean age 26 (SD 3) years] who had participated in European competitions for 3–10 years, were evaluated at the beginning of the 1992–93 season. Evaluation included a clinical history and physical examination, one and two-dimensional echocardiography, 12-lead resting electrocardiogram and a graded exercise test. Determination of the left ventricular mass index (LVMI) was performed using Devereux's formula with correction for the body surface area. Systolic and diastolic blood pressure were measured at rest and at peak exercise. Of the group 23 cyclists (58%) presented a LVMI greater than 130 g · m^–2, 21 cyclists presented a diastolic ventricular thickness equal to or greater than 13 mm, with a superior limit of 19 mm; 3 cyclists presented asymmetrical septum hypertrophy; and the relationship between posterior wall and left ventricular diastolic radius was equal to or greater than 0.45 in 14 cases (35%). Electrocardiographic abnormalities of ST-T segment were seen in only 1 subject. No correlation was found between the degree of ventricular hypertrophy and arterial blood pressure. We concluded that these professional cyclists showed a high prevalence of cardiac hypertrophy (58%). The distribution of this hypertrophy was concentric in 20/33 and asymmetric in 3/23 of the subjects with left ventricular hypertrophy. The electrocardiograms were normal in 98% of the subjects.     

Functional Effects of a Restrictive-Cardiomyopathy-Linked Cardiac Troponin I Mutation (R145W) in Transgenic Mice

The human cardiac troponin I (hcTnI) mutation R145W has been associated with restrictive cardiomyopathy. In this study, simultaneous measurements of ATPase activity and force in skinned papillary fibers from hcTnI R145W transgenic mice (Tg-R145W) were explored. Tg-R145W fibers showed an ∼ 13-16% increase in maximal Ca²⁺-activated force and ATPase activity compared to hcTnI wild-type transgenic mice. The force-generating cross-bridge turnover rate (g) and the energy cost (ATPase/force) were the same in all groups of fibers. Also, the Tg-R145W fibers showed a large increase in the Ca²⁺ sensitivity of both force development and ATPase. In intact fibers, the mutation caused prolonged force and intracellular [Ca²⁺] transients and increased time to peak force. Analysis of force and Ca²⁺ transients showed that there was a 40% increase in peak force in Tg-R145W muscles, which was likely due to the increased Ca²⁺ transient duration. The above cited results suggest that: (1) there would be an increase in resistance to ventricular filling during diastole resulting from the prolonged force and Ca²⁺ transients that would result in a decrease in ventricular filling (diastolic dysfunction); and (2) there would be a large (approximately 53%) increase in force during systole, which may help to partly compensate for diastolic dysfunction. These functional results help to explain the mechanisms by which these mutations give rise to a restrictive phenotype.     

Endothelial S1pr1 regulates pressure overload‐induced cardiac remodelling through AKT‐eNOS pathway

Cardiac vascular microenvironment is crucial for cardiac remodelling during the process of heart failure. Sphingosine 1‐phosphate (S1P) tightly regulates vascular homeostasis via its receptor, S1pr1. We therefore hypothesize that endothelial S1pr1 might be involved in pathological cardiac remodelling. In this study, heart failure was induced by transverse aortic constriction (TAC) operation. S1pr1 expression is significantly increased in microvascular endothelial cells (ECs) of post‐TAC hearts. Endothelial‐specific deletion of S1pr1 significantly aggravated cardiac dysfunction and deteriorated cardiac hypertrophy and fibrosis in myocardium. In vitro experiments demonstrated that S1P/S1pr1 praxis activated AKT/eNOS signalling pathway, leading to more production of nitric oxide (NO), which is an essential cardiac protective factor. Inhibition of AKT/eNOS pathway reversed the inhibitory effect of EC‐S1pr1‐overexpression on angiotensin II (AngII)‐induced cardiomyocyte (CM) hypertrophy, as well as on TGF‐β‐mediated cardiac fibroblast proliferation and transformation towards myofibroblasts. Finally, pharmacological activation of S1pr1 ameliorated TAC‐induced cardiac hypertrophy and fibrosis, leading to an improvement in cardiac function. Together, our results suggest that EC‐S1pr1 might prevent the development of pressure overload‐induced heart failure via AKT/eNOS pathway, and thus pharmacological activation of S1pr1 or EC‐targeting S1pr1‐AKT‐eNOS pathway could provide a future novel therapy to improve cardiac function during heart failure development.