The effect of He-Ne laser radiation on myocardium mechanical activity in rats

In isolated papillary muscles, a 5-minute irradiation with the He-Ne-laser Shuttle-1 enhances the maximal strength of isometric contraction and acceleration of relaxation. In physiological mode of mechanical loads, the irradiation with the laser red light enhances the myocardium contractability at all final systolic lengths with simultaneous enhancement of the isometric relaxation velocity at great systolic lengths and a deceleration of the relaxation at lesser lengths. Under the He-Ne-laser effect, restoration of rhythm-inotropic relationships occurred in the myocardium.     

Effect of vanadate and of removal of extracellular Ca2+ and Na+ on tension development and 45Ca efflux in rat and frog myocardium

Vanadate in the range 0-5 mM has positive inotropic effects on myocardial strips of frog and to a lesser extent on those of rat. Inhibiting the sarcolemmal Na+, Ca2+ exchange by a solution free of Ca2+ and Na+ caused a drop in 45Ca efflux and a transient increase in resting tension. These effects were more expressed for the frog than for the rat myocardium, which suggests that the Na+ for Ca2+ exchange across the cell membrane is more important in the frog than in the rat myocardium. A subsequent addition of vanadate at 2 or 5 mM had no effect on 45Ca efflux, while it increased the resting tension. This increase was higher for the frog than for the rat myocardium. These results suggest that the inotropic effects of vanadate may be due to an effect on membrane-bound Ca2+-ATPase.     

Mechanisms of the interaction of neurotransmitter systems

Interaction between different neurotransmitter systems has been revealed on various objects--the myocardium, identified, intact and internally perfused isolated neurons of molluscs. In frog myocardium, the inhibitory effect of adrenaline on cholinergic response may be simulated by theophylline and cholera toxin, i.e. the substances which indirectly increase intracellular content of cAMP. Another interaction reaction--inhibition of the response to adrenaline by acetylcholine--may be reproduced by imidazole, which decreases cAMP content due to activation of phosphodiesterase. Two types of interaction between serotonin and acetylcholine were revealed in the identified neurons of the snail Helix pomatia. In some of the neurons, serotonin increases acetylcholine depolarization, whereas in other ones decreases the latter. Both the increase and the decrease of responses to acetylcholine may be reproduced by theophylline. On intracellularly perfused neurons of Lymnaea stagnalis, modulation of acetylcholine responses of cell by biogenic amines was observed, the effect being induced by the drugs added not only to the surface membrane, but to intracellular medium as well.     

Peptides from the N-terminal domain of chromogranin A (vasostatins) exert negative inotropic effects in the isolated frog heart

The negative inotropic effects of synthetic peptides derived from the N-terminus of chromogranin A (CgA) were studied in an avascular model of the vertebrate myocardium, the isolated working frog heart (Rana esculenta). The peptides were frog and bovine CgA(4-16) and CgA(47-66), and bovine CgA(1-40) with (CgA(1-40SS)) and without an intact disulfide bridge (CgA(1-40SH)). Under basal cardiac conditions, four of the peptides caused a concentration-dependent negative inotropism that was comparable to the negative inotropy reported for human recombinant vasostatin I (CgA(1-78)) and bovine CgA(7-57). By comparison of the structural characteristics of the bovine and frog sequences with their minimally effective concentrations ranging from 68 to 125 nM of peptide, the results were consistent with the natural structure (CgA(17-38SS)) being essential for the negative inotropism. In addition, the partial sequences of the frog and bovine vasostatin I were effective in counteracting the characteristic positive inotropism exerted by isoproterenol (1 nM) at minimally effective concentrations ranging from 45 to 272 nM. Taken together, these results extend the first evidence for a cardiosuppressive role of the N-terminal domain of chromogranin A known for its co-storage with catecholamines in the sympathoadrenal system of vertebrates.     

An evidence for presynaptic excitatory alpha 2-adrenergic receptors in frog myocardium

This study was undertaken to determine the effects of clonidine on sympathetic neurotransmission in frog myocardium. In the electrically driven ventricular strips of frog heart, clonidine was found to be ineffective on contractility. However, clonidine increased the positive inotropic responses to transient additional stimulations. This effect of clonidine was antagonized by yohimbine, an alpha 2-adrenergic receptor antagonist. Clonidine did not change the positive inotropic effects of exogenously applied noradrenaline. These results suggest that clonidine facilitates sympathetic neurotransmission in frog myocardium via an action on alpha 2-adrenergic receptors located on sympathetic nerve terminals.     

Arterial perfusion of frog tongue for intracellular recording of taste cell receptor potential

The frog tongue was perfused through its artery with a Ringer solution using a peristaltic pump, and a method was developed to record stable intracellular receptor potentials of taste cells. Perfusing at 0.05 ml/min with a Ringer solution containing 5% dextran did not cause tongue edema, but perfusing at the same rate with Ringer without dextran caused edema. After perfusion at 0.05 ml/min with 100 mM K Ringer, the membrane potential of taste cells gradually decreased and reached a constant level in about 30 min, indicating that the intercellular fluid of the tongue could be replaced within this time period. While the artery of the frog tongue was perfused at 0.05 ml/min with Ringer containing 5% dextran, intracellular receptor potentials of taste cells elicited by four basic taste stimuli (1 M NaCl, 10 mM quinine-HCl (Q-HCl), 1 mM acetic acid and 1 M galactose) were similar to those obtained from the control taste cells under normal blood flow.     

Influence of lithium upon the intracellular potential of frog skin epithelium.

The effect of Li upon the intracellular potential of frog skin (Rana esculenta) was investigated. In the range between 1 and 25 mM Li in the epithelial bathing solution, a semilogarithmic linear relationship between [Li] and intracellular potential under short circuit conditions was obtained. The intracellular potential at all [Li] is quantitatively sufficient to explain the previously reported accumulation of Li in the intracellular space of the frog skin epithelium (Leblanc, G. 1972. Pfluegers Arch. 337:1) on the basis of a passibe entrance step at the outer border. A reduction of the intracellular potential by Li is also observed in the presence of 6 mM Na in the epithelial bathing solution. Consequences regarding the mechanism of uptake of Na across the outer border of the frog skin are discussed.     

The State of Water in Polarized and Depolarized Frog Nerves: A Proton Magnetic Resonance Study

The high resolution proton magnetic resonance spectrum of the sciatic nerve of the frog was studied in both the polarized and depolarized states. Paramagnetic salts were introduced into the system in order to separate the signals from the intra- and extracellular environments. It was determined that about 65% of the proton signal from the nerve trunk was accounted for by the intracellular environment in the polarized nerve trunk and that this percentage decreased to about 34% in the depolarized case.

The temperature dependence of the line widths of the intracellular proton signal was studied. The enthalpy and entropy of activation for proton exchange between the intra- and extracellular environments were found to be 11.1 kcal/mole and -17.1 cal/deg-mole respectively. The pseudo-first-order rate constant for proton exchange between the intra- and extracellular environments was determined at 20°C and shown to agree with the measured permeability coefficients of similar cells.

Data are presented which indicate that the pseudo-first order rate constant for proton exchange between the two environments decreases upon depolarization of the nerve trunk and that the proton spin-spin relaxation time of the protons of intracellular water decreases significantly with depolarization.

These results indicate a possibly quite important role of water in neural phenomena.

     

Calcium-dependent chloride transient currents in the immature oocyte of the frog, Rana esculenta

Transient currents of chloride were studied in the plasma membrane of immature frog oocyte in voltage clamp conditions. The transients appeared to be activated by an influx of Ca2+ from the external medium. The mechanism leading to a surge of intracellular Ca2+ concentration needed at least 30 sec before full recovery. It was inhibited by substituting Ba2+ for Ca2+ in the external medium, or in the presence of La3+, Co2+ and Cd2+, or when external Na+ was replaced by Li+. Verapamil proved ineffective. The data suggest that an intracellular system of Ca-activated Ca-release is present in the frog oocyte, which can be primarily activated by membrane hyperpolarization via an influx of Ca2+ through non-selective channels.     

Mitochondrial respiratory control in the myocardium

The heart muscle has proved to be a practical model for studying respiratory control in intact tissues. It also demonstrates that control at the level of the respiratory chain is augmented by metabolic control at the substrate level as exemplified by the very narrow range of changes in the redox state of the mitochondrial NADH/NAD couple even during extensive changes in ATP and oxygen consumption. The behaviour of mitochondria when isolated can largely be duplicated in the intact myocardium. Moreover, the high intracellular concentrations of enzymes, coenzymes and adenine nucleotides create conditions of high reaction rates, enabling the formation of a near equilibrium network of certain main pathways. This equilibrium network in connection with metabolic regulation of the hydrogen pressure upon the matrix NADH/NAD pool is a prerequisite for the regulation of cellular respiration at a high efficiency of energy transfer. Experimentation on the intact myocardium also seems to be capable of resolving some of the uncertainties about prevailing mechanisms for the regulation of cellular respiration.     

The participation of the cAMP intracellular signal system in the olfactory transduction of camphor and amyl alcohol]

In the frog isolated olfactory epithelium, the cAMP intracellular signal system was shown to take part in olfactory transduction of amyl alcohol but not camphor.     

Identification of a major enzyme for the synthesis and hydrolysis of cyclic ADP-ribose in amphibian cells and evolutional conservation of the enzyme from human to invertebrate

Cyclic ADP-ribose (cADPR), a metabolite of NAD(+), is known to function as a second messenger for intracellular Ca(2+) mobilization in various vertebrate and invertebrate tissues. In this study, we isolated two Xenopus laevis cDNAs (frog cd38 and cd157 cDNAs) homologous to the one encoding the human cADPR-metabolizing enzyme CD38. Frog CD38 and CD157 are 298-amino acid proteins with 35.9 and 27.2 % identity to human CD38 and CD157, respectively. Transfection of expression vectors for frog CD38 and CD157 into COS-7 cells revealed that frog CD38 had NAD(+) glycohydrolase, ADP-ribosyl cyclase (ARC), and cADPR hydrolase activities, and that frog CD157 had no enzymatic activity under physiological conditions. In addition, when recombinant CD38 and frog brain homogenate were electrophoresed on an SDS-polyacrylamide gel, ARC of the brain homogenate migrated to the same position in the gel as that of frog CD38, suggesting that frog CD38 is the major enzyme responsible for cADPR metabolism in amphibian cells. The frog cd38 gene consists of eight exons and is ubiquitously expressed in various tissues. These findings provide evidence for the existence of the CD38-cADPR signaling system in frog cells and suggest that the CD38-cADPR signaling system is conserved during vertebrate evolution.     

Sodium Ions in the Electromechanical Coupling System of Myocardium and Skeletal Muscles of the Frog Rana temporaria

The role of the transsarcolemmal Na⁺ gradient in providing phasic contraction of myocardium and skeletal muscles of the common frog Rana temporaria was studied. It was shown that a decrease of the gradient by means of total or partial substitution of Na⁺ for Ch⁺ or Li⁺ produced a tissue-specific reduction of the isometric tension developed by the muscles as well as of the maximum rate of its development. The functional mechanisms of use of the Na⁺-gradient for intracellular mobilization of activator of the muscle contraction, Ca²⁺ ions, are considered, and the experimental evidences for significance of this gradient increase to provide intensification of the process of activation of the discrete (single, rhythmic) contraction of vertebrate phasic muscles are presented. The revealed differences between the studied muscles reflect adaptive rearrangement levels of ionic mechanisms of the electromechanical coupling system in these muscles, which are achieved in the course of evolution of their contractile function.     

Sodium-free contractures in frog myocardium damaged by catecholamines

1. Sodium-free contractures were studied in myocardial strips from R. pipiens with extracellular sodium (Na+o) replaced by choline chloride and extracellular calcium (Ca2+o) varied with EGTA-buffer. Normal myocardium was compared with that damaged by adrenaline (ADR) or isoproterenol (ISO). 2. Frog myocardium, damaged by in vivo injections of catecholamines, remained relaxed when exposed to Na+/Ca2+-free solutions. Only in 2 out of 18 experiments were small contractures observed after several hours. 3. Addition of KCN to the Na+/Ca2+-free solution caused small contractures after several hours in 7 out of 10 experiments. 4. The time to maximum Na+-free contractures was correlated to Ca2+o in a dose-dependent manner, but not influenced by catecholamine-induced myocardial damage. 5. Cell injury in the frog heart after in vivo injections of catecholamines does not affect the sarcolemmal Na+/Ca2+-exchange and is not associated with passive leakage of Ca2+ from the extracellular to the intracellular space.     

Is the change in intracellular pH during fatigue large enough to be the main cause of fatigue?

The intracellular pH of frog sartorius muscles exposed to an extracellular pH 8.0 (25 mM HCO3-, 1% CO2) was 6.9-7.1. Following a fatiguing stimulation period (one tetanic contraction per second for 3 min), the intracellular pH was 6.5-6.7. When similar experiments were repeated with frog sartorius muscles exposed to pH 6.4 (2mM HCO3-, 1% CO2), the intracellular pH was 6.8-6.9 at rest and 6.3-6.4 following fatigue. So, in both experiments the intracellular pH decreased by 0.4-0.5 pH unit during fatigue. When the CO2 concentration of the bathing solution was increased from 1 to 30%, the intracellular pH of resting muscles decreased from 7.0 to 6.2-6.3. Although the effect of CO2 on the intracellular pH was greater than the fatigue effect, the decrease in tetanic force with CO2 was less than 40%, while during fatigue the tetanic force decreased by at least 70%. Therefore in frog sartorius muscle the decrease in tetanic force during fatigue exceeds the decrease that is expected from just a change in intracellular pH.     

Oscillations and chaos behind predator-prey invasion: mathematical artifact or ecological reality?

A constant dilemma in theoretical ecology is knowing whether model predictions corrspond to real phenomena or whether they are artifacts of the modelling framework. The frequent absence of detailed ecological data against which models can be tested gives this issue particular importance. We address this question in the specific case of invasion in a predator-prey system with oscillatory population kinetics, in which both species exhibit local random movement. Given only these two basic qualitative features, we consider whether we can deduce any properties of the behaviour following invasion. To do this we study four different types of mathematical model, which have no formal relationship, but which all reflect our two qualitative ingredients. The models are: reaction-diffusion equations, coupled map lattices, deterministic cellular automata, and integrodifference equations. We present results of numerical simulations of the invasion of prey by predators for each model, and show that although there are certain differences, the main qualitative features of the behaviour behind invasion are the same for all the models. Specifically, there are either irregular spatiotemporal oscillations behind the invasion, or regular spatiotemporal oscillations with the form of a periodic travelling ''wake'', depending on parameter values. The observation of this behaviour in all types of model strongly suggests that it is a direct consequence of our basic qualitative assumptions, and as such is an ecological reality which will always occur behind invasion in actual oscillatory predator-prey systems.     

Influence of lithium upon the intracellular potential of frog skin epithelium

Summary The effect of Li upon the intracellular potential of frog skin (Rana esculenta) was investigated. In the range between 1 and 25mm Li in the epithelial bathing solution, a semilogarithmic linear relationship between [Li] and intracellular potential under short circuit conditions was obtained. The intracellular potential at all [Li] is quantitatively sufficient to explain the previously reported accumulation of Li in the intracellular space of the frog skin epithelium (Leblanc, G. 1972.Pfluegers Arch. 337:1) on the basis of a passive entrance step at the outer border. A reduction of the intracellular potential by Li is also observed in the presence of 6mm Na in the epithelial bathing solution. Consequences regarding the mechanism of uptake of Na across the outer border of the frog skin are discussed.     

Derivation of the Macroscopic Intracellular Conductivity of Deformed Myocardium on the Basis of Microstructure Analysis

Biophysics - A model of changes in the intracellular conductivity of the myocardium due to its deformation was developed. Macroconductivities were derived using the microstructure-based model...