Protection by iloprost of the myocardial contractility and rhythmicity in frog ventricular strips

Summary Incubation of frog ventricular strips with Ringer containing iloprost for 24 h at 4°C can protect the contractility and rhythmicity from heat stimulation and aconitine when compared with strips incubated in Ringer alone under the same experimental conditions.The authors are grateful to Dr E. Schillinger, Schering Research Laboratories, Berlin, W.-Germany, for kindly supplying iloprost (ZK 36 374). This work was supported by a grant from the Turkish Scientific and Technical Research Council (TAG-480).     

Adenosine is a sensitive oxygen sensor in the heart

Cardiac adenosine is formed both by an oxygen-sensitive (AMP----adenosine) and by an oxygen-insensitive (S-adenosylhomocysteine----adenosine) pathway. The phasic adenosine release during beta-adrenergic stimulation with isoproterenol is closely linked to coronary venous PO2 (isolated heart) and can be almost fully prevented when diastolic aortic pressure is maintained constant (heart in situ). During pressure autoregulation the transmural gradient of free adenosine is only increased when the autoregulatory reserve is exhausted. The critical PO2 below which adenosine formation is enhanced was found to be 3 mm Hg (isolated cardiomyocytes). Collectively, these data indicate that the formation of adenosine is not primarily coupled to the energy expenditure of the heart but to the supply/demand ratio for oxygen.     

Transmural pressure as a determinant of basic intrinsic heart rate

Summary It was observed the heart rate was minimum at zero transmural pressure. The mean heart rate at zero transmural pressure was 23±5/min. This mean heart rate increased from 23±5/min to a peak value of 40±6/min (74% acceleratin) when the transmural pressure was raised from 0 to +4 mm Hg and to a similar peak value of 36±8/min (56% acceleration) when the transmural pressure was lowered from 0 to –4 mm Hg. The peak values attained at ±4 mm Hg were higly significant (p<0.001). It is concluded that the heart rate at zero transmural pressure represents the basic intrinsic pacemaker frequency independent of neural, humoral, thermal and haemodynamically induced mechanical influences.     

The influence of hydrostatic pressure on the rate of hydrolysis of acetylcholine and contractility in the vagal heart system

Zusammenfassung Die Acetylcholin-Esterase-Aktivität und die Kontraktilität wird am isolierten Frosch-Herzen unter steigendem hydrostatischem Druck untersucht. Ohne wesentliche Veränderung der Molekül-Dimension wird ein Anstieg der Hydrolyse von Acetylcholin bewirkt.

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National Academy of Sciences, National Research Council, Senior postdoctoral Resident Research associate.     

Circadian rhythmicity in phosphorylase activity and glycogen content in the heart muscle of the scorpion,Heterometrus fulvipes,C.L. Koch

Summary Maximal activity levels of phosphorylase A and AB at 20.00 h alternate with minimal levels at 08.00 h of the day, while the glycogen content exhibited a reverse trend in the heart of the scorpion,Heterometrus fulvipes.Acknowledgment. The authors thank Prof. K.S. Swami, for providing facilities. The financial assistance rendered by UGC (to VJ) and ICMR (to DCR) is gratefully acknowledged.     

Persistent circadian rhythmicity of protein synthesis in the liver of starved rats

Zusammenfassung Die Aufnahme von³H-Leucin in das Lebereiweiss wurde während der Dunkelphase ihres Tag-Nachtzyklus bei fastenden Ratten untersucht. Die übliche rhythmische Aufnahme von³H-Leucin wurde durch die Fastenperiode nicht verhindert, obwohl die Menge des aufgenommenen³H-Leucin zwei zeitlich verschiedene Maxima aufwies.

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This investigation was supported by Grant No. GB 8306 from the United States National Science Foundation.     

Stretch receptors in the eye muscles of a teleost fish

Summary Extraocular muscles of a teleost fish,Girella tricuspidata, contain a predominantly phasic stretch receptor, which consists of fine beaded nerve terminals within the red portion of the muscle.The authors are grateful to Mr V. Straznik for supplying the fish, and to Mrs M. Fisher for histological assistance. Financial support for this work was received from the New Zealand Medical Research Council and the Auckland University Research Committee and University Grants Committee.     

Motilities of isolated and aggregated mice; A difference in ultradian rhythmicity

Summary Isolated mice display higher locomotor activity and greater sensitivity to d-amphetamine than aggregated mice. Ultradian motility rhythms can be shown to differ both quantitatively and qualitatively between isolated and aggregated mice.This study was supported in part by Centro Ramón y Cajal and Fundación Juan March. Present address of F.V.D. is Centre de Neurochimie, 11 rue Humann, F-67085 Strasbourg Cédex (France).     

Effects of caffeine on the contractility and membrane potentials of rat atrium

Zusammenfassung Der Einfluss von Coffein auf Kontraktion und Membranpotential des Atriums der Ratte ergibt: Verkürzung der Dauer des Aktionspotentials und Beschleunigung der Geschwindigkeit von Repolarisation und Depolarisation. Ein möglicher Zusammenhang dieser Änderungen mit der erhöhten Kontraktilität wird diskutiert.

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This work was supported by a grant from the Life Insurance Medical Fund.     

External strontium and contractility in single giant muscle fibers of the barnacle

Summary Isometric tension and membrane potential in response to electrical stimulation have been studied on single giant muscle fibers of the barnacle upon replacement of external calcium with strontium. Under these conditions, the membrane response showed after the normal peak depolarization, a plateau phase lasting 3–7 sec before repolarization took place, while the force of contraction showed a linear relation with external strontium concentration. A direct action of strontium ions on contractile proteins (namely troponin) can be ruled out in favor of a triggering action on the sarcoplasmic reticulum, which, in turn, leads to calcium release and development of tension.Acknowledgment. I wish to thank Dr C. C. ashley in whose laboratory the research reported in this paper was performed, and Mrs L. M. Castell for invaluable technical assistance. This work was supported by grant No. 106140/048104235 from Consiglio Nazionale delle Ricerche, Italy.     

Pyruvate dehydrogenase kinase regulatory mechanisms and inhibition in treating diabetes, heart ischemia, and cancer

The fraction of pyruvate dehydrogenase complex (PDC) in the active form is reduced by the activities of dedicated PD kinase isozymes (PDK1, PDK2, PDK3 and PDK4). Via binding to the inner lipoyl domain (L2) of the dihydrolipoyl acetyltransferase (E2 60mer), PDK rapidly access their E2-bound PD substrate. The E2-enhanced activity of the widely distributed PDK2 is limited by dissociation of ADP from its C-terminal catalytic domain, and this is further slowed by pyruvate binding to the N-terminal regulatory (R) domain. Via the reverse of the PDC reaction, NADH and acetyl-CoA reductively acetylate lipoyl group of L2, which binds to the R domain and stimulates PDK2 activity by speeding up ADP dissociation. Activation of PDC by synthetic PDK inhibitors binding at the pyruvate or lipoyl binding sites decreased damage during heart ischemia and lowered blood glucose in insulin-resistant animals. PDC activation also triggers apoptosis in cancer cells that selectively convert glucose to lactate. Received 25 August 2006; received after revision 20 November 2006; accepted 20 December 2006     

Effect of nicotine on the transmembrane potential and contractility of isolated rat atria

Zusammenfassung Die Wirkungen von Nikotin auf die Kontraktilität und die Membranpotentiale des Rattenatriums wurden untersucht. Nikotin (5 × 10^–4 M) erhöhte gleichzeitig die entwickelte Spannung sowie die Dauer und Fläche des Aktionspotentials. Ein möglicher Zusammenhang dieser Änderungen mit der erhöhten Kontraktilität wird diskutiert.

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Deceased 22 July 1966.