Frog Ventricle Research Articles

Electrophysiological differences in cholinergic signaling between the hearts of summer and winter frogs (Rana temporaria).

The striking seasonal difference in sensitivity of frog cardiac muscle to acetylcholine or stimulation of parasympathetic nervous fibers has been noted almost a century ago, although its electrophysiological basis has never been revealed. The present study compares the effects of the muscarinic agonist carbamylcholine chloride (CCh 10-8-10-5M) on electrical activity in isolated atrial and ventricular preparations from dormant frogs (Rana temporaria) caught in January (winter-acclimatized, WA) and from active frogs caught in July (summer-acclimatized, SA). Seasonal differences in the density of potassium acetylcholine-dependent current (IKACh) were also studied in atrial and ventricular myocytes from both summer and winter groups. In atrial myocardium, CCh produced concentration-dependent shortening of action potentials (APs). CCh concentration producing a 50% reduction of AP duration was lower in WA (1.03 × 10-7M) than SA atria (2.7 × 10-7M). 10-6M CCh induced drastic reduction of AP amplitude rendering the tissue unexcitable in both WA or SA atrial preparations. Ventricular preparations showed greater seasonal difference in CCh sensitivity. While 10-6M induced inexcitability in 50% of tested WA preparations, in SA preparations even 10-5M CCh was without effect. This striking difference between cholinergic effects in SA and WA frog ventricle could be explained by seasonal changes in the IKACh density. The density of IKACh induced by 10-5M CCh and measured at 0mV was 14.4 ± 3.45pA/pF in WA, but only 1.5 ± 0.4pA/pF in SA atrial cells. In ventricular cells, the respective values were 2.61 ± 0.56 and 0.71 ± 0.09pA/pF. Thus, hibernating winter frog has a much greater electrophysiological cholinergic response than active summer frog due to up-regulation of IKACh.

Venomic and pharmacological activity of Acanthoscurria paulensis (Theraphosidae) spider venom

In the present study we conducted proteomic and pharmacological characterizations of the venom extracted from the Brazilian tarantula Acanthoscurria paulensis, and evaluated the cardiotoxicity of its two main fractions. The molecular masses of the venom components were identified by mass spectrometry (MALDI-TOF-MS) after chromatographic separation (HPLC). The lethal dose (LD50) was determined in mice. Nociceptive behavior was evaluated by intradermal injection in mice and the edematogenic activity by the rat hind-paw assay. Cardiotoxic activity was evaluated on in situ frog heart and on isolated frog ventricle strip. From 60 chromatographic fractions, 97 distinct components were identified, with molecular masses between 601.4 and 21,932.3 Da. A trimodal molecular mass distribution was observed: 30% of the components within 500-1999 Da, 38% within 3500–5999 Da and 21% within 6500–7999 Da. The LD50 in mice was 25.4 ± 2.4 μg/g and the effects observed were hypoactivity, anuria, constipation, dyspnea and prostration until death, which occurred at higher doses. Despite presenting a dose-dependent edematogenic activity in the rat hind-paw assay, the venom had no nociceptive activity in mice. Additionally, the venom induced a rapid blockage of electrical activity and subsequent diastolic arrest on in situ frog heart preparation, which was inhibited by pretreatment with atropine. In the electrically driven frog ventricle strip, the whole venom and its low molecular mass fraction, but not the proteic one, induced a negative inotropic effect that was also inhibited by atropine. These results suggest that despite low toxicity, A. paulensis venom can induce severe physiological disturbances in mice.

Role of Calcium and Potassium Channels in Effects of Hydrogen Sulfide on Frog Myocardial Contractility

The effects of sodium hydrosulfide NaHS, a donor of hydrogen sulfide H2S, on the force of muscle contraction were examined on isolated myocardial strips from frog ventricles. NaHS decreased the amplitude of muscle contractions in a dose-dependent manner under normal conditions and during inhibition of Ca channels with nifedipine. In contrast, under conditions of blockade of ATP-dependent potassium channels with glibenclamide, NaHS exerted a positive inotropic effect from the first minute of application. Neither blockade, nor activation of ATP-dependent K-channels with glibenclamide modulated the negative inotropic effect of NaHS. Inhibition of K-channels with tetraethylammonium (TEA) (3, 5, 10 mM) or 4-aminopyridine increased the amplitude of myocardial contractions. Preliminary application of 4-aminopyridine or TEA (3 mM) did not eliminate NaHS-induced negative inotropic effect, although higher TEA concentrations (5 or 10 mM) prevented it. The data indicate that the targets of H(2)S in frog myocardium are ATP-dependent, Ca-activated, and voltage-dependent K-channels.

Resident and circulating mast cells in propulsative organs of frog Rana temporaria

Mast cells (MCs) of the "blood" and lymph hearts of the adult frog Rana temporaria were investigated at histochemical and ultrastructural levels. Two populations of MCs were revealed in these propulsative organs: population of resident MCs and population of circulating MCs. It has been shown that the resident cardiac MCs have an oval or elongated form and are located between atrial or ventricular myocytes and under endocardial endothelium. The resident cardiac MCs are situated in connective tissue of epicardium, too. Avascular myocardium of the frog ventricle consists of a spongy network of muscle trabeculae. We revealed circulating MCs in intertrabecular spaces and clefts of the spongy myocardium and in the blood of the main central cavity. Circulating MCs are round in shape and contain a large central nucleus enriched with condensed chromatin. They resemble the lymphocytes, but show cytoplasm filled with granules. These granules ultrastructure is much like that of the granules of the cardiac resident MCs. In the lymph heart, oval and somewhat elongated resident MCs are located in the interstitial space among cross-striated muscle fibers and among smooth muscle cells of tubular (afferent and efferent) valves. Sometimes lymphocyte-like circulating MCs are revealed in the cavity of lymph heart. Circulating MCs are also present in the lymphatics located adjacent to the lymph hearts. In certain parts of the lymphatic walls MCs are in close adhesion to the mesothelial cells lining the lymphatic cavity. Our histochemical investigation revealed that both the resident and circulating MCs of the propulsative organs give a strongly positive reaction with alcian blue, but weakly red with safranin and weakly metachromatic with toluidine blue. The presence of population of circulating MCs in the frog suggests that there are differences in biology of MCs between lower and higher vertebrates.

Action of oxidative reactions in mitochondria on contractivity of heart muscle. Effects of Ni2+

Inotropic effect of Ni2+ on mitochondrial oxidative reactions were studied on myocardium preparations excised from the left frog ventricle and the rat heart mitochondria (RHM), respectively. In the presence of 10–200 μM Ni2+, the cardiac contraction amplitude increased in the dose-dependent manner. It has been found that Ni2+ is not toxic for RHM. The state 4 by Chance in the KCl medium was stimulated by 100 μM Ni2+. At the same time, Ni2+ did not affect the state 3 and the 2,4-dinitrophenol-stimulated respiration of RHM. Our findings allow suggesting that the Ni2+-induced increase in the cardiac contraction amplitude is affected by energy state of the rat cardiomyocytic mitochondria.

Lüttgau & Niedergerke; the classic study of calcium–sodium antagonism half a century on

Lüttgau & Niedergerke; the classic study of calcium–sodium antagonism half a century on

A comparative study of contractility of the heart ventricle in some ectothermic vertebrates

The purpose of this study was to analyze contractility of the heart ventricle in selected reptilian and amphibian species having the same ventricular excitation pattern. Systolic time intervals and indices of contractility of the heart ventricle were measured in anaesthetized frogs, snakes, and tortoises by use of polycardiography. The electromechanical delay was significantly shorter in tortoises compared with the other two species. The isovolumetric contraction time in frogs was approximately twofold longer than in reptiles. The pre-ejection period was the longest in frogs and the shortest in tortoises, whereas snakes were intermediate. The ejection time was slightly longer in tortoises compared with the other two species. The greatest isovolumetric contraction index and the smallest myocardial tension index corresponded to the frog and tortoise heart ventricle, respectively. The intrasystolic index in tortoises was significantly greater than in frogs, whereas quite similar to that in snakes. The frog ventricle had lower contractility compared with the reptilian one. Although ventricular contractility tended to be lower in snakes compared with tortoises, this difference was not statistically significant. Possible causes for these differences are discussed. We suppose a large variety in ventricular contractility among amphibian and reptilian species having the same ventricular activation pattern. This variety may be conditioned by heart anatomy, intracardiac shunting, lifestyles, and habitats. It can only be hypothesized that on the average, ventricular contractility is higher in reptiles compared with amphibians and in chelonians compared with snakes.

Diastolic Mechanical Properties of Vascular and Avascular Hearts

Background: In vertebrates, there are two kinds of myocardium, compacta and spongiosa, which are associated with blood supply systems i.e. coronary and sinusoidal circulation. To characterize the diastolic properties of these two types of ventricles, we analyzed the ventricular end-diastolic pressure-volume relationships (EDPVR) in rat and frog heart that include integrated expression of chamber geometry and passive material properties of myocardial wall.Methods: Pressure of rat left ventricule and frog ventricule was recorded to obtain EDPVRs under isovolumic contractions with increases of ventricular volume to ∼10 mmHg. The curvature changes of EDPVRs were described by non-linear function. (EDP = α•EDV6 + β).Results: Ventricular volumes were normalized by ventricular weights. The volumes from rat and frog ventricles that provided pressure of 10 mmHg were 0.6 and 2.5 mL/g respectively. EDPVRs from rat and frog showed common shape (see Figure). The values of α were 349 ± 39 and 0.677 ± 0.120 (n = 3) in rats and frogs respectively.Discussion: Frog spongy ventricles showed higher expandability than rat left ventricles composed of compact myocardium. Compact myocardium with coronary circulation might trade ventricular expandability in return for higher contractility.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Association between decreased intra-thoracic impedance and ventricular tachyarrhythmias

The increased risk of ventricular tachyarrhythmias (VT) in the congestive heart failure (CHF) population has been well described [ [1] Bigger Jr., J.T. Fleiss J.L. Kleiger R. Miller J.P. Rolnitzky L.M. The relationships among ventricular arrhythmias, left ventricular dysfunction, and mortality in the 2 years after myocardial infarction. Circulation. 1984; 69: 250-258 Crossref PubMed Scopus (1079) Google Scholar ]. The concept of mechanical–electrical feedback has been proposed as a potential mechanism for the observed clinical relationship between CHF and VT in multiple animal [ 2 Lab M.J. Mechanically dependent changes in action potentials recorded from the intact frog ventricle. Circ Res. 1978; 42: 519-528 Crossref PubMed Scopus (110) Google Scholar , 3 Franz M.R. Cima R. Wang D. Profitt D. Kurz R. Electrophysiological effects of myocardial stretch and mechanical determinants of stretch-activated arrhythmias. Circulation. 1992; 86: 968-978 Crossref PubMed Scopus (356) Google Scholar , 4 Hansen D.E. Craig C.S. Hondeghem L.M. Stretch-induced arrhythmias in the isolated canine ventricle. Evidence for the importance of mechanoelectrical feedback. Circulation. 1990; 81: 1094-1105 Crossref PubMed Scopus (253) Google Scholar , 5 Parker K.K. Lavelle J.A. Taylor L.K. Wang Z. Hansen D.E. Stretch-induced ventricular arrhythmias during acute ischemia and reperfusion. J Appl Physiol. 2004; 97: 377-383 Crossref PubMed Scopus (20) Google Scholar ] and computer [ 6 Healy S.N. McCulloch A.D. An ionic model of stretch-activated and stretch-modulated currents in rabbit ventricular myocytes. Europace. 2005; 7: 128-134 Crossref PubMed Scopus (39) Google Scholar , 7 Kohl P. Hunter P. Noble D. Stretch-induced changes in heart rate and rhythm: clinical observations, experiments and mathematical models. Prog Biophys Mol Biol. 1999; 71: 91-138 Crossref PubMed Scopus (228) Google Scholar ] models. Despite these reports, the dynamic relationship between pulmonary congestion/decompensated heart failure and VT in the clinical environment is not well understood. A new cardiac defibrillator/cardiac resynchronization therapy (CRT-D) system is capable of ambulatory monitoring of ventricular arrhythmias as well as intra-thoracic fluid using thoracic impedance. The system records a daily mean impedance value and calculates an index of net pulmonary fluid accumulation [ [8] Yu C.M. Wang L. Chau E. et al. Intrathoracic impedance monitoring in patients with heart failure: correlation with fluid status and feasibility of early warning preceding hospitalization. Circulation. 2005; 112: 841-848 Crossref PubMed Scopus (555) Google Scholar ]. An acute decrease in intra-thoracic impedance has been previously correlated with an increase in left ventricular filling pressure [ [8] Yu C.M. Wang L. Chau E. et al. Intrathoracic impedance monitoring in patients with heart failure: correlation with fluid status and feasibility of early warning preceding hospitalization. Circulation. 2005; 112: 841-848 Crossref PubMed Scopus (555) Google Scholar ]. We report a case of repeated VT episodes preceded by acutely lowered thoracic impedance.

Contractile recovery from acidosis in toad ventricle is independent of intracellular pH and relies upon Ca2+ influx

Hypercapnic acidosis produces a negative inotropic effect on myocardial contractility followed by a partial recovery that occurs in spite of the persistent extracellular acidosis. The underlying mechanisms of this recovery are far from understood, especially in those species in which excitation-contraction coupling differs from that of the mammalian heart. The main goal of the present experiments was to obtain a better understanding of these mechanisms in the toad heart. Hypercapnic acidosis, induced by switching from a bicarbonate-buffered solution equilibrated with 5% CO2 to the same solution equilibrated with 12% CO2, evoked a decrease in contractility followed by a recovery that reached values higher than controls after 30 min of continued acidosis. This contractile pattern was associated with an initial decrease in intracellular pH (pHi) that recovered to control values in spite of the persistent extracellular acidosis. Blockade of the Na+/H+ exchanger (NHE) with cariporide (5 micromol l-1) produced a complete inhibition of pHi restitution, without affecting the mechanical recovery. Hypercapnic acidosis also produced a gradual increase of diastolic and peak Ca2+i transient values, which occurred immediately after the acidosis was settled and persisted during the mechanical recovery phase. Inhibition of Ca2+ influx through the reverse mode of the Na+/Ca2+ exchanger (NCX) by KB-R (1 micromol l-1 for myocytes and 20 micromol l-1 for ventricular strips), or of L-type Ca2+ channels by nifedipine (0.5 micromol l-1), completely abolished the mechanical recovery. Acidosis also produced an increase in the action potential duration. This prolongation persisted throughout the acidosis period. Our results show that in toad ventricular myocardium, acidosis produces a decrease in contractility, due to a decrease in Ca2+ myofilament responsiveness, followed by a contractile recovery, which is independent of pHi recovery and relies on an increase in the influx of Ca2+. The results further indicate that both the reverse mode NCX and the L-type Ca2+ channels, appear to be involved in the increase in intracellular Ca2+ concentration that mediates the contractile recovery from acidosis.

Antimicrobial activity of the bufadienolides marinobufagin and telocinobufagin isolated as major components from skin secretion of the toad Bufo rubescens

The increase in the emergence of antibiotic-resistant microorganisms and difficult to treat infections caused by these pathogens stimulate research aiming the identification of novel antimicrobials. Skin secretion of amphibian contains a large number of biologically active compounds, including compounds that performance defense mechanisms against microorganisms. In the present work, two antimicrobial bufadienolides, telocinobufagin (402.1609 Da) and marinobufagin (400.1515 Da), were isolated from skin secretions of the Brazilian toad Bufo rubescens. The specimens were collected in Brasilia (Distrito Federal, Brazil), the skin secretions extracted by electric stimulation, and submitted to purification by RP-HPLC. The molecular structure and mass determination were done by 1H and 13C NMR and mass spectrometry data, respectively. The antimicrobial activity was performed by liquid growth inhibition against Staphylococcus aureus and Escherichia coli. The minimum inhibitory concentrations of telocinobufagin and marinobufagin were, respectively, 64.0 and 16.0 μg/mL for E. coli and both 128 μg/mL for S. aureus. Besides the antimicrobial activity both bufadienolides promoted an increase of the contraction force in isolated frog ventricle strips.

Effects of cardiac glycosides, phenylglyoxal (PGO) and ryanodine on contractile responses in skinned single fibers from frog ventricle

Effects of cardiac glycosides, phenylglyoxal (PGO) and ryanodine on contractile responses in skinned single fibers from frog ventricle

Indirect cardiotoxic activity of the caecilian Siphonops paulensis (Gymnophiona, Amphibia) skin secretion

The skin secretion of the caecilian S. paulensis has an indirect cardiotoxic effect. It induces a rapid blockage of electrical activity and subsequent diastolic arrest on in situ toad heart preparations. This action is not blocked by atropine and is therefore not mediated through a cholinergic mechanism. In addition, S. paulensis skin secretion is ineffective in inducing any response in isolated perfused toad heart assay, in the spontaneously beating isolated toad atria or in the electrically driven toad ventricle strip. These results, and the observation that S. paulensis skin secretion exhibits an hemolytic activity ([Schwartz, E. F., Schwartz, C. A., Sebben, A., Mendes E. G. (1997) Cardiotoxic and hemolytic activities on the caecilian Siphonops paulensis skin secretion. J. Venom. Anim. Toxins 3(1), 190]), suggest that the skin secretion cardiotoxicity could be mediated through an endogenous agent. The cardiotoxic action of S. paulensis skin secretion was investigated in isolated toad cardiac tissues in the presence of toad red blood cells (TRBC). In both atria and ventricle it evoked the same responses observed in the in situ heart. The potassium concentrations of the suspending media, as determined by atomic absorption spectroscopy were 9.5 and 11.7 times greater, respectively, in the presence of TRBC than in its absence. Given that increased levels of potassium also showed a negative inotropic effect in the isolated ventricle strip, the action of the skin secretion was attributed to the hemolytic activity, which causes an increase in K + concentration of the medium.

P-611 - Effects of phenylglyoxal (PGO) and cardiac glycosides, isoprenaline and ryanodine on contractile responses in single fibers from frog ventricle

P-611 - Effects of phenylglyoxal (PGO) and cardiac glycosides, isoprenaline and ryanodine on contractile responses in single fibers from frog ventricle

Dose-dependent reduction of cardiac transmembrane potential by high-intensity electrical shocks

Cardiac tissue dysfunction can result from high-intensity electrical shocks and is manifested as changes in transmembrane potential (Vm). Ten-millisecond shock pulses (SPs) of varying intensity and polarity were applied to frog ventricle in diastole, and Vm was quantified directly under the stimulating electrode by an optical method using voltage-sensitive dye. As SP intensities were increased, the shock-induced action potential (AP) plateau and AP amplitude (APAs) decreased sigmoidally toward 75-85% of the control AP amplitude (APAc) and zero, respectively. APAs was shifted toward lower current densities for anodal compared with cathodal SPs (half-maximal values 185 and 238 mA/cm2, respectively; P = 0.02). Recovery of APAs was marginally significant 1 s after SP delivery (P = 0.063). The peak change in Vm during SP (across all intensity levels) was -200% APAc for anodal and +125% APAc for cathodal pulses. In conclusion, we show that SP reduces APA in a sigmoidal fashion at strengths > 10-20 x diastolic threshold and is more deleterious for anodal polarities.

The effect of some peptides from the hibernating brain on Ca 2+ current in cardiac cells and on the activity of septal neurons

The effects of the peptides TSKYR and DY isolated from the brain of hibernating ground squirrels on Ca 2+ current were studied. TSKYR activated Ca 2+ current in frog auricle fibers and in single cells from frog ventricle whereas DY blocked Ca 2+ current in both preparations. In isolated rat and ground squirrel cardiocytes, TSKYR had no effect on Ca 2+ current, and DY increased it. In brain slices of rat, DY blocked the activity of medial septal neurons. TSKYR increased activity of septal neurons at the initial phase, which was followed by decrease of neuronal activity.

The reconstruction of dynamic 3D structure of biological objects using stereo microscope images

In this paper, we address the analysis of 3D shape and shape change in non-rigid biological objects imaged via a stereo light microscope. We propose an integrated approach for the reconstruction of 3D structure and the motion analysis for images in which only a few informative features are available. The key components of this framework are: 1) image registration using a correlation-based approach, 2) region-of-interest extraction using motion-based segmentation, and 3) stereo and motion analysis using a cooperative spatial and temporal matching process. We describe these three stages of processing and illustrate the efficacy of the proposed approach using real images of a live frog's ventricle. The reconstructed dynamic 3D structure of the ventricle is demonstrated in our experimental results, and it agrees qualitatively with the observed images of the ventricle.

A modification of receptor theory. 1956.

A modification of receptor theory. 1956.

P-463 - Effects of phenylglyoxal (PGO) and acetyl-strophanthidin(AS) on contractile responses in single fibers from frog ventricle

P-463 - Effects of phenylglyoxal (PGO) and acetyl-strophanthidin(AS) on contractile responses in single fibers from frog ventricle

Characterization of Adrenoceptor Types and Subtypes in American Bullfrogs Acclimated to Warm or Cold Temperature

While indirect evidence suggested that the responsiveness of frog adrenoceptors changes in response to temperature, direct measurement of adrenoceptor binding following acclimation to warm and cold temperatures had not been done. In the present study, the radioligands [3H]prazosin, [3H]RX821002, and [125I]cyanopindolol were used to label and quantify α1-, α2-, and β-adrenoceptors in bullfrogs acclimated to warm or cold environments. The number of α1-, α2-, and β-adrenoceptors in atrium, ventricle, and kidney membranes was not significantly different between warm- and cold-acclimated frogs. Characterization of receptor subtypes using pharmacological antagonists demonstrated that α2-adrenoceptors in frog spinal cord and kidney were of the same pharmacological subtype, which is similar to the mammalian α2A-subtype. The β-adrenoceptor in frog ventricle, atrium, and kidney was the β2-subtype. These results suggest that while the α1-, α2-, and β-adrenoceptor types have evolved in the frog, multiple subtypes of adrenoceptors are not necessary for physiological regulation in this species.