The cephalopod heart: The evolution of a high-performance invertebrate pump

Cephalopods typically have high metabolic rates. They have blood in which the oxygen carrier is haemocyanin, a pigment that is found only in solution and which never seems to be present in concentrations that will transport more than 4–5 vols % of oxygen. Their hearts must in consequence have very high cardiac outputs. In this account the performance of the heart ofNautilus, the only surviving ectocochleate, is contrasted with the performance of the hearts of coleoids,Octopus which has a relatively low metabolic rate (for a coleoid) and squids which have very high oxygen uptakes by any standards. In all these animals, heartbeat frequency is temperature-dependent and the additional oxygen demand in exercise is met very largely by a 2–3-fold increase in stroke volume. With the exception ofNautilus, cephalopods tend to utilise nearly all of the oxygen transported in the blood even at rest; they show very limited factorial scopes. Specific power output has, however, increased dramatically from 2.7 mWg^–1 in an activeNautilus to 5.5 mWg^–1 inOctopus and up to 20 or 30 mWg^–1 in species ofLoligo. The increase is almost entirely due to a 10-fold increase in heartbeat frequency. It is argued that frequency cannot be used as a means of responding to extra demand in an animal that must also carry automatic compensation for changes in metabolic rate dependent upon the ambient temperature, and that the use of frequency in some squid may be associated with a reduced temperature tolerance. Cephalopod systemic hearts do not scale directly with body mass, like the hearts of fish and the higher vertebrates. Smaller cephalopods have relatively larger hearts (as Mass^0.9). A typical 100-g coleoid would have a heart mass of 0.15 g. Oegopsid squids appear to be exceptional with hearts twice as large.     

Über die Wirkung von Prostaglandin E1 auf den Ca-Haushalt isolierter Meerschweinchenherzen

Summary The stimulatory effect of PGE₁ on different functions of isolated guinea-pig hearts (Langendorff method, Tyrode solution) was coupled with an increase in the rate of⁴⁵Ca uptake from the perfusion medium. The total myocardial Ca content and the amount of exchangeable cellular Ca were not affected. This action of PGE₁ on the myocardial Ca metabolism seems to be related to the positive inotropic action of PGE₁ and can most probably be explained by an increase in the membrane permeability to Ca ions (similar to the action of epinephrine).     

Down-regulation of sodium current in chronic heart failure: effect of long-term therapy with carvedilol

Evidence has accumulated recently about the importance of alterations in Na⁺ channel function and slow myocardial conduction for arrhythmias in the infarcted and failing heart. The present study tested a hypothesis that Na⁺ current (I_Na/C) density decreases in chronic heart failure (HF) and that Na⁺ channel (NaCh) functional density can be restored by long-term therapy with carvedilol, a mixed α- and β-adrenergic blocker. Studies were performed using a canine model of chronic HF produced in dogs by sequential intracoronary embolizations with microspheres. HF developed approximately 3 months after the last embolization (left ventricle, LV, ejection fraction = 28 ± 1 %). Ventricular cardiomyocytes (VCs) were isolated enzymatically from LV mid-myocardium, and I_Na was measured by whole-cell patch-clamp. The maximum I_NA/C was decreased in failing (n = 19) compared to normal (n = 12) hearts (33.1 ± 1.6 vs 48.5 ± 5.1 pA/pF, mean ± SE, p < 0.001). The steady-state inactivation and activation of I_Na remained unchanged in failing compared to normal hearts. Long-term treatment with carvedilol (1 mg/kg, twice daily for 3 months) normalized I_Na/C in dogs with HF. I_Na/C in HF dogs (n = 6) treated with carvedilol was higher compared to that of non-treated HF dogs (n = 6) (49.4 ± 0.9 vs 29 ± 4.8 pA/pF, p < 0.007). In vitro culture of VCs of failing hearts for 24 h did not restore I_Na/C. However, I_Na/C was partially restored when VCs were incubated for 24 h with BAPTA-AM, an intracellular Ca²⁺ buffer. Thus, we conclude that experimental chronic HF in dogs results in down-regulation of the functional density of NaCh that can be restored by long-term therapy with carvedilol. The mechanism of NaCh down-regulation in HF may be linked to poor Ca²⁺ handling in this stage of disease. Received 4 June 2002; received after revision 1 July 2002; accepted 17 July 2002 RID="*" ID="*"Corresponding author.     

Successful cryopreservation of auricle fragments from rat hearts at −196°C

Summary The influence of electrolyte composition and glucose concentration of a cryprotective medium on the survival of auricle fragments from adult rat hearts after storage at –196°C was investigated. Using a K⁺-, Mg⁺⁺-, Ca⁺⁺-rich solution with increased glucose concentration, a high rate of surviving fragments was found after cryopreservation.     

Molekulargewichtsbestimmung von Kalbsherzmyosin

Summary Sedimentation and diffusion coefficients, partial specific volume, intrinsic viscosity, ATP-ase activity and molecular weight of cardiac myosin from calf hearts were determined. The values agree well with the results ofMueller et al.⁴ for cardiac myosin of the dog, and are not essentially different from values reported for skeletal myosins.¹      

Comparative analysis of phospholamban phosphorylation in crude membranes of vertebrate hearts

Summary Phospholamban, a sarcoplasmic reticulum phosphoprotein, is present in the hearts of mammalian, avian, amphibian, and fish species. Phylogenetic changes are indicated by marked differences among species in cardiac phospholamban content and by the absence of Ca²⁺/calmodulin-dependent phospholamban phosphorylation at an early developmental stage.     

Role of nitric oxide in the functional response to ischemia-reperfusion of heart mitochondria from hyperthyroid rats

We investigated the role of nitric oxide (NO) in the mitochondrial derangement associated with the functional response to ischemia-reperfusion of hyperthyroid rat hearts. Mitochondria were isolated at 3000 g from hearts subjected to ischemia-reperfusion, with or without N-nitro-L-arginine (L-NNA, an NO synthase inhibitor). During reperfusion, hyperthyroid hearts displayed tachycardia and low functional recovery. Their mitochondria exhibited O₂ consumption similar to euthyroid controls, while H₂O₂ production, hydroperoxide, protein-bound carbonyl and nitrotyrosine levels, and susceptibility to swelling were higher. L-NNA blocked the reperfusion tachycardic response and increased inotropic recovery in hyperthyroid hearts. L-NNA decreased mitochondrial H₂O₂ production and oxidative damage, and increased respiration and tolerance to swelling. Such effects were higher in hyperthyroid preparations. These results confirm the role of mitochondria in ischemia-reperfusion damage, and strongly suggest that NO overproduction is involved in the high mitochondrial dysfunction and the low recovery of hyperthyroid hearts from ischemia-reperfusion. L-NNA also decreased protein content and cytochrome oxidase activity of a mitochondrial fraction isolated at 8000 g. This and previous results suggest that the above fraction contains, together with light mitochondria, damaged mitochondria coming from the heaviest fraction, which has the highest cytochrome oxidase activity and capacity to produce H₂O₂. Therefore, we propose that the high mitochondrial susceptibility to swelling, favoring mitochondrial population purification from H₂O₂-overproducing mitochondria, limits hyperthyroid heart oxidative stress.Received 24 March 2004; received after revision 9 June 2004; accepted 5 July 2004     

Photodynamic sensitizers assay: rapid and sensitive iodometric measurement

A rapid, sensitive and simple spectrophotometric method for the detection of¹O₂ produced by photodynamic photosensitizers in slightly acid and air-saturated aqueous solutions has been developed. The method is based on the reaction of¹O₂ (produced by photodynamic processes) with I^– in the presence of ammonium molybdate as a catalyst. The reaction product I₃ ^–, proportional to¹O₂, is followed spectrophotometrically at 355 nm. Several ways of avoiding interference with other oxidizing compounds, either present before or produced during the irradiation, are described.The method could be used to measure the efficiency of water-soluble photodynamic photosensitizers.     

Amounts of nuclear DNA in anurans of the USSR

Summary The amounts of nuclear DNA in blood erythrocytes of 18 species of Anura from the USSR have been determined to be in the range of 4.0–20.6 pg (10^–12 g). Brown frogs of genusRana have lower mean genome sizes than green frogs. Palaearctic Anura, as a whole, have a greater content of nuclear DNA than the species of the same families from regions further south.     

Mechanical parameters determined in dispersed ventricular heart cells

A high-resolution laser diffraction system suitable for studying the basic mechanical properties of small contractile single cells has been developed. This method was used to establish the mechanical behavior of 95 ventricular cells isolated from adult guinea pig hearts. During contraction, the sarcomere length shortened from 1828 +/- 43 nm (mean +/- SD) to 1518 +/- 99 nm. The maximal velocities were 1.98 +/- 0.64 micron/s for shortening and 1.93 +/- 0.54 micron/s for re-lengthening. The twitch duration from 20% shortening to 80% re-lengthening was 622 +/- 120 ms.     

Die Wirkung von Theophyllin auf den cellulären Ca-Stoffwechsel des Warmblüterherzens

Summary In isolated, electrically driven, left guineapig atria, theophylline (5×10^–4 g/ml) increased the rate of⁴⁵Ca uptake and release without affecting the total myocardial Ca content and the amount of exchangeable cellular Ca. In sheep and calf heart preparations, theophylline (10^–4–10^–3 g/ml) increased Ca inward current during excitation (as examined indirectly by Ca dependent changes of membrane potential in TTX-containing solutions) as well as tension development. It is concluded that the positive inotropic effect of theophylline in mammalian hearts is due to an increase in Ca influx during the excitation process.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

Cell size of mammalian myocardia is not related to physiological demand

Morphological characteristics of myocardial ventricular myocytes have been evaluated from 5 mammalian orders with resting heart rates ranging from 51 to 475 bpm. The purpose was to determine if morphological characteristics of the myocardia are related to the functional demand imposed on the cell as represented by the resting heart rate. Cell size is a constant among mammals of different sizes which have different physiological demands. In contrast, there is more mitochondrial area and less myofibrillar area per cell in animals with rapidly beating hearts than in animals with slower heart rates. Additionally, the mean cross sectional area of individual myofibrils is 30% larger in the cow as compared to the mouse. These findings combined with our previous studies indicate that the different functional requirements of myocardia from different mammalian orders are satisfied by intracellular adaptations of both a structural and biochemical nature.     

Cell size of mammalian myocardia is not related to physiological demand

Morphological characteristics of myocardial ventricular myocytes have been evaluated from 5 mammalian orders with resting heart rates ranging from 51 to 475 bpm. The purpose was to determine if morphological characteristics of the myocardia are related to the functional demand imposed on the cell as represented by the resting heart rate. Cell size is a constant among mammals of different sizes which have different physiological demands. In contrast, there is more mitochondrial area and less myofibrillar area per cell in animals with rapidly beating hearts than in animals with slower heart rates. Additionally, the mean cross sectional area of individual myofibrils is 30% larger in the cow as compared to the mouse. These findings combined with our previous studies indicate that the different functional requirements of myocardia from different mammalian orders are satisfied by intracellular adaptations of both a structural and biochemical nature.     

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     

Some extracellular matrix elements as markers of 'capillary tunnels' in hypertrophied rat heart.

We studied the distribution of the extracellular matrix proteins fibronectin (FN) and laminin (LM) in the hypertrophied hearts of spontaneously hypertensive rats (SHR), using an immunofluorescence method with specific antibodies. The immunohistochemical reaction was positive in the cytoplasm of some hypertrophied cardiomyocytes. The results showed that FN and LM can be used as markers for tunnels, i.e. intracardiocytic invaginations of the sarcolemma. The tunnels observed contained capillaries.     

Some extracellular matrix elements as markers of ‘capillary tunnels’ in hypertrophied rat heart

We studied the distribution of the extracellular matrix proteins fibronectin (FN) and laminin (LM) in the hypertrophied hearts of spontaneously hypertensive rats (SHR), using an immunofluorescence method with specific antibodies. The immunohistochemical reaction was positive in the cytoplasm of some hypertrophied cardiomyocytes. The results showed that FN and LM can be used as markers for tunnels, i.e. intracardiocytic invaginations of the sarcolemma. The tunnels observed contained capillaries.     

Über die Beeinflussung der Ca-Aufnahme in Lipidextrakte aus Mikrosomen und Mitochondrien des Herzens durch Digitoxin

Summary Lipids were isolated by chloroform-methanol extraction from mitochondrial and microsomal fractions of guinea-pig hearts. In the presence of digitoxin (10^–9-10^–6 g/ml) 15–30% more radioactive Ca was taken up by the lipid extracts than under control conditions, but the total amount of Ca in this phase remained unchanged. Thus, digitoxin produced an increase in the specific activity of the lipid-bound Ca which may be explained by an increased exchangeability of this Ca fraction. This effect of digitoxin might result in an improved availability of the lipid-bound Ca for Ca-dependent functions (e.g. contraction) of the heart muscle cell.     

Roles of melatonin and its receptors in cardiac ischemia–reperfusion injury

Acute myocardial infarction (AMI) has been an economic and health burden in most countries around the world. Reperfusion is a standard treatment for AMI as it can actively restore blood supply to the ischemic site. However, reperfusion itself can cause additional damage; a process known as cardiac ischemia/reperfusion (I/R) injury. Although several pharmacological interventions have been shown to reduce tissue damage during I/R injury, they usually have undesirable effects. Therefore, endogenous substances such as melatonin have become a field of active investigation. Melatonin is a hormone that is produced by the pineal gland, and it plays an important role in regulating many physiological functions in human body. Accumulated data from studies carried out in vitro, ex vivo, in vivo, and also from clinical studies have provided information regarding possible beneficial effects of melatonin on cardiac I/R such as attenuated cell death, and increased cell survival, leading to reduced infarct size and improved left-ventricular function. This review comprehensively discusses and summarizes those effects of melatonin on cardiac I/R. In addition, consistent and inconsistent reports regarding the effects of melatonin in cases of cardiac I/R together with gaps in surrounding knowledge such as the appropriate onset and duration of melatonin administration are presented and discussed. From this review, we hope to provide important information which could be used to warrant more clinical studies in the future to explore the clinical benefits of melatonin in AMI patients.     

Molecular mechanisms of glutamate-dependent neurodegeneration in ischemia and traumatic brain injury

Stroke and neurotrauma mediate neuronal death through a series of events that involve multiple interdependent molecular pathways. It has been suggested that these pathways are triggered following elevations in extracellular excitatory amino acids, primarily glutamate [1]. This report outlines mechanisms involving glutamate-mediated excitotoxicity with specific focus on (i) the role of Ca²⁺ in neurotoxicity, (ii) The concept of source specificity of neurotoxicity, (iii) the role of the ionotropic N-methyl-D-aspartate (NMDA)-subtype glutamate receptor and its associated submembrane molecules that may give rise to signaling specificity in excitotoxicity and (iv) the role of glutamate-mediated free-radical generation and associated cell death pathways. We also highlight a novel, peptide-based approach for uncoupling NMDA receptors from excitotoxicity in the rat central nervous system subjected to focal ischemia, thereby reducing stroke infarct volume and improving neurological functioning.Received 11 August 2003; received after revision 15 September 2003; accepted 17 September 2003