Relationship between action potential, contraction-relaxation pattern, and intracellular Ca2+ transient in cardiomyocytes of dogs with chronic heart failure

Abnormalities of contractile function have been identified in cardiomyocytes isolated from failed human hearts and from hearts of animals with experimentally induced heart failure (HF). The mechanism(s) responsible for these functional abnormalities are not fully understood. In the present study, we examined the relationship between action potential duration, pattern of contraction and relaxation, and associated intracellular Ca²⁺ transients in single cardiomyocytes isolated from the left ventricle (LV) of dogs (n = 7) with HF produced by multiple sequential intracoronary microembolizations. Comparisons were made with LV cardiomyocytes isolated from normal dogs. Action potentials were measured in isolated LV cardiomyocytes by perforated patch clamp, Ca²⁺ transients by fluo 3 probe fluorescence, and cardiomyocyte contraction and relaxation by edge movement detector. HF cardiomyocytes exhibited an abnormal pattern of contraction and relaxation characterized by an attenuated initial twitch (spike) followed by a sustained contracture ('dome') of 1 to 8 s in duration and subsequent delayed relaxation. This pattern was more prominent at low stimulation rates (58% at 0.2 Hz, n = 211, 21% at 0.5 Hz, n = 185). Measurements of Ca²⁺ transients in HF cardiomyocytes at 0.2 Hz manifested a similar spike and dome configuration. The dome phase of both the contraction/relaxation pattern and Ca²⁺ transients seen in HF cardiomyocytes coincided with a sustained plateau of the action potential. Shortening of the action potential duration by administration of saxitoxin (100 nM) or lidocaine (30 μM) reduced the duration of the dome phase of both the contraction/relaxation profile as well as that of the Ca²⁺ transient profile. An increase of stimulation rate up to 1 Hz caused shortening of the action potential and disappearance of the spike-dome profile in the majority of HF cardiomyocytes. In HF cardiomyocytes, the action potential and Ca²⁺ transient duration were not significantly different from those measured in normal cells. However, the contraction-relaxation cycle was significantly longer in HF cells (314 ± 67 ms, n = 21, vs. 221 ± 38 ms, n = 46, mean ± SD), indicating impaired excitation-contraction uncou pling in HF cardiomyocytes. The results show that, in cardiomyocytes isolated from dogs with HF, contractile abnormalities and abnormalities of intracellular Ca²⁺ transients at low stimulation rates are characterized by a spike-dome configuration. This abnormal pattern appears to result from prolongation of the action potential. Received 22 January 1998; received after revision 16 March 1998; accepted 27 March 1998     

Phytanic acid impairs mitochondrial respiration through protonophoric action

Refsum disease is a rare, inherited neurodegenerative disorder characterized by accumulation of the dietary branched-chain fatty acid phytanic acid in plasma and tissues caused by a defect in the alphaoxidation pathway. The accumulation of phytanic acid is believed to be the main pathophysiological cause of the disease. However, the exact mechanism(s) by which phytanic acid exerts its toxicity have not been resolved. In this study, the effect of phytanic acid on mitochondrial respiration was investigated. The results show that in digitonin-permeabilized fibroblasts, phytanic acid decreases ATP synthesis, whereas substrate oxidation per se is not affected. Importantly, studies in intact fibroblasts revealed that phytanic acid decreases both the mitochondrial membrane potential and NAD(P)H autofluorescence. Taken together, the results described here show that unesterified phytanic acid exerts its toxic effect mainly through its protonophoric action, at least in human skin fibroblasts. Received 4 August 2007; received after revision 26 September 2007; accepted 10 October 2007 J. C. Komen, F. Distelmaier: These authors contributed equally to this work.     

Amebacidal action of cycloserine

Zusammenfassung Endamoeba histolytica wird durch Cycloserin abgetötet. Diese amöbizide Wirkung wird durch Adenin und Guanin teilweise verhindert und durch Adenosin, Guanosin, Adenylsäure, Guanylsäure und 2,6-Diaminopurin vollständig aufgehoben.     

Mutagenic action of ethylene halogenhydrins

Zusammenfassung Eine stark mutagene Wirkung wird durch äthylenchlorhydrin, äthylenbromhydrin und äthylenjodhydrin aufKlebsiella pneumoniae ausgeübt.     

Comparative aspects of structure and action of molluscan neuropeptides

A number of neuropeptides were isolated from the ganglia and muscles of molluscs, and their actions were examined. Diverse neuropeptides, in addition to several classical neurotransmitters, were suggested to be involved in the regulation of the anterior byssus retractor muscle ofMytilus. A wide structural variety of members of theMytilus inhibitory peptide family was observed in each of the generaMytilus, Achatina andHelix. Gly-Trp-NH₂, the C-terminal dipeptide fragment of the neuropeptide AGPWamide, showed a more potent action than the parent peptide in all of the muscles examined. Peptides related to some molluscan neuropeptides were found to be distributed interphyletically. Some neuropeptides containing ad-amino acid residue were found inAchatina andMytilus. These aspects of molluscan neuropeptides are thought not to be exceptional.     

Mechanism of action of boseimycin

Zusammenfassung Unmittelbar nach Zugabe von Boseimycin zuB. subtilis werden Wachstum und Proteinsynthese verhindert. DNA und RNA werden erst später beeinflusst. Die hemmende Wirkung von Boseimycin auf die behandelten Zellen ist nach Waschung mit Phosphatpuffer reversibel.     

Fungistatic action of aflatoxin B1

Résumé La croissance des plusieurs espèces d'Aspergillus et dePenicillium dans un milieu modifié de Czapek a été inhibitée par l'aflatoxin B₁. Cet arrêt de croissance pourrait être annulé en substituant au nitrate de sodium un extrait de levure comme source d'azote.

---

---

This is a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U.S. Department of Agriculture.     

High K+ content explains the abolition of the action potential in amphibian sciatic nerve in vitro byLathyrus sativus seed extract

Summary The action potential in amphibian sciatic nerve in vitro has been reported to be abolished by the topical application ofLathyrus sativus seed extract. We have confirmed this effect, but find that it is probably caused by the high K⁺ content of such seed extracts and that organic neurotoxins are not implicated.Acknowledgments. We thank the Wellcome Trust for financial support, Professor M.W. Bradbury for help with the ion determinations and Miss M.B. Burbridge of the Tropical Products Institute, London, for obtaining seed from Bombay, India.     

Functional interaction between TRPC1 channel and connexin-43 protein: a novel pathway underlying S1P action on skeletal myogenesis

We recently demonstrated that skeletal muscle differentiation induced by sphingosine 1-phosphate (S1P) requires gap junctions and transient receptor potential canonical 1 (TRPC1) channels. Here, we searched for the signaling pathway linking the channel activity with Cx43 expression/function, investigating the involvement of the Ca²⁺-sensitive protease, m-calpain, and its targets in S1P-induced C2C12 myoblast differentiation. Gene silencing and pharmacological inhibition of TRPC1 significantly reduced Cx43 up-regulation and Cx43/cytoskeletal interaction elicited by S1P. TRPC1-dependent functions were also required for the transient increase of m-calpain activity/expression and the subsequent decrease of PKCα levels. Remarkably, Cx43 expression in S1P-treated myoblasts was reduced by m-calpain-siRNA and enhanced by pharmacological inhibition of classical PKCs, stressing the relevance for calpain/PKCα axis in Cx43 protein remodeling. The contribution of this pathway in myogenesis was also investigated. In conclusion, these findings provide novel mechanisms by which S1P regulates myoblast differentiation and offer interesting therapeutic options to improve skeletal muscle regeneration.     

Cytotoxic action of nucleic acids

Zusammenfassung Mit einer letalen Dosis von Dimethyl-Myleran vorbehandelte Mäuse überleben nach Transfusion isologer Knochenmarkzellen. Wirken Nukleinsäurenin vitro auf die Knochenmarkzellen ein, so ist ihre lebenserhaltende Kapazität vermindert.

---

---

This investigation was supported by grants to the Chester Beatty Research Institute (Institute of Cancer Research: Royal Cancer Hospital, London) from the Medical Research Council, the British Empire Cancer Campaign, the Anna Fuller Fund and the National Cancer Institute of the National Institutes of Health, U.S. Public Health Service.     

The antifertility action ofa-chlorohydrin: Enzyme inhibition bya-chlorohydrin phosphate

Summary Preparations of the enzymes glyceraldehyde-3-phosphate dehydrogenase and triosephosphate isomerase are shown to be inhibited bya-chlorohydrin phosphate (II) in a competitive and non-competitive manner, respectively.a-Chlorohydrin (I), glycidol and epi-chlorohydrin have no inhibitory activities suggesting that their antifertility actions are due to their metabolism in vivo toa-chlorohydrin phosphate.     

Cardiotonic action of 3-deoxydigitoxigenin

Zusammenfassung Die Herzwirksamkeit von 3-Deoxydigitoxigenin am isolierten Froschherzen wurde geprüft. Im Gegensatz zur bisherigen Auffassung (3-Hydroxygruppe notwendig für kardiotonische Wirkung der Digitalis-Verbindungen) zeigte 3-Deoxydigitoxigenin eine starke kardiotonische Aktivität.     

The mode of action of four anthelmintics

Résumé LesAscaris qui se sont «déparalysés» après une incubation prolongée dans 100 ppm de levamisole, ne se contractent pas après injection des anthélminitiques béphenium, méthyridine et pyrantel. Etant donné que la mécamyline et la pempidine bloquent les contractions desAscaris provoquées par le levamisole, il paraît probable que chez les Nématodes ces 4 anthélmintiques sont des stimulateurs des ganglions.     

N-bromosuccinimide action on creatine phosphokinase

Zusammenfassung Behandlung von Kreatinphosphokinase mit überschüssigemN-Bromsuccinimid bewirkt eine Umwandlung der vorhandenen peptidartig gebundenen Tryptophanreste, welche sich durch die für diesen Vorgang charakteristische Veränderung des Spektrums anzeigt. Am unbehandelten Enzym liessen sich auch mit einem grossen Überschuss von NBS keine freien endständigen NH₂-Gruppen eindeutig nachweisen.

---

---

This work was aided by a grant from the Muscular Dystrophy Associations of America, Inc.     

Strain-specific action of division-inhibiting agents inBacterium anitratum

Zusammenfassung Es wird die stammspezifische Wirkung von Sulphathiazol auf 2 verschiedene Stämme desBacterium anitratum beschrieben und diskutiert.     

Protective action of irradiated bone marrow cells

Zusammenfassung Wurdein vitro röntgenbestrahltes Knochenmark (475r, 950 r, 1425 r) in letal bestrahlte Mäuse (LD 100/11=950 r) injiziert, so ergab sich: Isologes Knochenmark, mit 950 r bestrahlt, besitzt noch beachtliche Schutzwirkung; bestrahltes homologes und heterologes Knochenmark war weniger oder ganz inaktiv.     

R M values and biological action of testosterone esters

Zusammenfassung Eigene Befunde zum Zusammenhang zwischenR _M -Werten und biologischer Wirkung von Testosteron-Estern werden mit denjenigen vonBiagi (Experientia27, 918 (1971)) verglichen und diskutiert. Durch Anwendung geeigneter chromatographischer Phasen können allgemeiner gültige und mathematisch ausdrückbare Resultate erhalten werden.     

5-Thio-d-glucose:o-diphenoloxidase inhibition as its mechanism of action

Summary 5-Thio-d-glucose completely inhibitedo-diphenoloxidase from animal as well as plant sources. It has been reported that thioglucose suppresses spermatogenesis in mice and also insect metamorphosis, probably through inhibition of glucose transport. Inhibition ofo-diphenoloxidase (which is active in spermatozoa and insect larvae) is suggested as an alternative mechanism of action of thioglucose.     

Mechanism of action of CDP-choline in parkinsonism

Zusammenfassung Es ist anzunehmen, dass CDP-Cholin (Cytidin-Diphosphat-Cholin) auf Verminderung von Dopamin im Nucleus caudatus einen signifikanten (0.001<p<0.01) Abwehreffekt ausübt, was durch homolaterale Destruktion der Substantia nigra verursacht wird.     

The action of conformationally restricted analogues of GABA onLimulus andHelix central neurones

Summary Intracellular recordings have been made from GABA sensitive neurones in the central nervous system ofLimulus andHelix. The following conformationally restricted analogues of GABA all possessed GABA-like activity onLimulus neurones andHelix excitatory GABA receptors: muscimol, thiomuscimol, THIP, isoguvacine and piperidine-4-carboxylic acid. It is suggested that GABA interacts with these receptors in a partially extended and almost planar conformation.