Developmental changes in dopamine modulation of the heart in the isopod crustacean Ligia exotica: reversal of chronotropic effect

Developmental changes in dopamine modulation of the heart were examined in the isopod crustacean Ligia exotica. The Ligia cardiac pacemaker is transferred from the myocardium to the cardiac ganglion during juvenile development and the heartbeat changes from myogenic to neurogenic. In the myogenic heart of early juveniles, dopamine affected the myocardium and caused a decrease in the frequency and an increase in the duration of the myocardial action potential, resulting in negative chronotropic (decrease in beat frequency) and positive inotropic (increase in contractile force) effects on the heart. Contrastingly, in the heart of immature adults just after juvenile development, dopamine caused effects of adult type, positive chronotropic and positive inotropic effects on the heart affecting the cardiac ganglion and myocardium. During the middle and late juvenile stages, dopamine caused individually a negative or a positive chronotropic effect on the heart. These results suggest that the chronotropic effect of dopamine on the Ligia heart is reversed from negative to positive in association with the cardiac pacemaker transfer from the myocardium to the cardiac ganglion during juvenile development.     

Developmental changes in heart photosensitivity of the isopod crustacean Ligia exotica

During juvenile development, the cardiac pacemaker of the isopod crustacean Ligia exotica is transferred from the myocardium to the cardiac ganglion of the neurogenic heart. In adult, light stimulus decreases the beat frequency of the heart. To elucidate developmental changes in the photosensitivity of the juvenile Ligia heart, we examined the effect of a light stimulus on the semi-isolated heart of juveniles at various developmental stages by the recording membrane potential of the myocardium. We also examined the effect of hyperpolarizing current injection into the myocardium, because this causes different effects on the beat frequency between myogenic and neurogenic hearts. In newly hatched juveniles, beat frequency decreased upon current injection but exhibited no response to white light. In contrast, 10 days after hatching, beat frequency did not change upon current injection, but decreased in response to white light. The heart photoresponse of juveniles was reversibly eliminated by application of tetrodotoxin, which changes the heartbeat from neurogenic to myogenic by suppressing cardiac ganglion activity. The proportion of juveniles exhibiting a heart photoresponse increased gradually up to 100% during the period between 3 and 10 days after hatching. The results suggest that the heart photoresponse of L. exotica appears in association with transfer of the cardiac pacemaker from the myocardium to the cardiac ganglion during juvenile development.     

Cardioacceleratory Neurons of the Isopod Crustacean, Ligia exotica: Visualization of Peripheral Projection onto the Heart Muscle

Innervation of the heart muscle by the cardioacceleratory neurons was morphologically and electrophysiologically examined in the isopod crustacean, Ligia exotica. Intracellular injection of neurobiotin into the first and second cardioacceleratory neurons (CA1 and CA2) revealed their peripheral axonal projections. Inside the heart, the CA1 and CA2 axons ran along the trunk of the cardiac ganglion. Finely arborized branches with many varicosities arose from the axon and projected over the heart muscle. Stimulation of either the CA1 or CA2 axon caused an overall depolarization in the muscle of a quiescent heart. The amplitude of the depolarization increased with increasing stimulus frequency. During stimulation, the membrane resistance of the heart muscle decreased. In a beating heart, the cardioacceleratory nerve stimulation caused multiple effects on the heart muscle activity and the heartbeat. The results suggest that the cardioacceleratory neurons of Ligia exotica regulate the amplitude of the heartbeat (inotropic effect) and the heart tonus (tonotropic effect) via the synaptic contacts on the heart muscle, while the heartbeat frequency (chronotropic effect) is regulated via the synapses on the cardiac ganglion neurons.     

Cardiac pacemaker mechanisms in the ostracod crustacean Vargula hilgendorfii

The heart of the ostracod crustacean Vargula hilgendorfii has a single intrinsic neuron that morphologically appears to innervate the myocardium. We, therefore, examined the heart activity electrophysiologically to determine whether the heartbeat is neurogenic. Each heartbeat is associated with a myocardial action potential composed of a spike potential followed by a plateau potential. The frequency of the action potential is not stable but changes successively over a wide range. The action potential is not preceded by a pacemaker potential and has an inflection in its rising phase. The myocardial cells couple electrically and fire almost simultaneously. The frequency of the action potential was unchanged by injection of depolarizing or hyperpolarizing current into the myocardium. However, slow oscillatory potentials appeared during the depolarization and its frequency was higher with increasing current intensity. Application of 1-microM tetrodotoxin (TTX) depolarized the myocardial membrane and completely prevented the action potential. During this depolarization, slow oscillatory potentials often appeared spontaneously. These results suggest that, although the myocardium has a property of conditional oscillator, the heartbeat is driven by the single cell cardiac ganglion that has both pacemaker and motor functions.     

Photosensitive neurogenic heart of the isopod crustacean Ligia exotica

The heart of animals is regulated through the central nervous system in response to external sensory stimuli. We found, however, that the adult neurogenic heart of the isopod crustacean Ligia exotica has photosensitivity. The beat frequency of the isolated heart decreased in response to a light stimulus. Magnitude of the response was stimulus intensity dependent and the heartbeat frequency decreased to less than 80% of the dark value during illumination of the white light with an intensity of 6.0 mW cm-2. The spectral sensitivity curve of the heart photoresponse peaked at a wavelength around 520 nm. In response to 530 nm monochromatic light, the relationship between light intensity and response magnitude was linear and the threshold intensity was 7.26 x 1012 quanta cm-2 s-1. Bursting activity of the cardiac ganglion, which is located in the heart and acts as the cardiac pacemaker deceased in frequency in response to illumination by white light. This fact suggests that the heart photoresponse of L. exotica results from the photosensitivity of the cardiac ganglion neurons. The photoresponse of the heart therefore contributes to regulation of cardiac output in addition to other regulatory systems.     

Aminergic modulation of the myogenic heart in the branchiopod crustacean Triops longicaudatus

Although crustaceans typically have a neurogenic heart, the primitive crustacean Triops longicaudatus has a myogenic heart with the heartbeat arising from the endogenous rhythmic activity of the myocardium. In the present investigation, the effects of six biogenic amines, epinephrine, norepinephrine, dopamine, octopamine, serotonin and histamine, on the myogenic heart of T. longicaudatus were examined. Epinephrine, norepinephrine, dopamine and octopamine accelerated the heartbeat, increasing both the frequency and amplitude of the action potential of the myocardium in a concentration dependent manner. The ability of epinephrine and norepinephrine to produce the acceleratory effects was more potent than that of dopamine and octopamine; the threshold concentrations of epinephrine and norepinephrine were approximately 10(-10) M and those of dopamine and octopamine approximately 10(-7) M. Serotonin weakly inhibited the heartbeat, decreasing both the frequency and amplitude of the myocardial action potential in a concentration dependent manner with a threshold concentration of approximately 10(-6) M. Histamine exhibited no effect on the heartbeat. The results provide the first evidence for direct effects of amines on the crustacean myocardium and suggest neurohormonal regulation of the myogenic heart in T. longicaudatus.     

Cardioregulatory nerves in the spider Eurypelma marxi Simon

The objective of this study was to locate nerves arising from the CNS that have a cardioregulatory function in the tarantula, Eurypelma marxi Simon. Ramifications of the paired abdominal nerve VIIIb merge with the cardiac ganglion within the first heart segment. Electrical stimulation of the branches of nerve VIIIb that connect with the cardiac ganglion produce changes in heartbeat rate and amplitude. Nerve cutting experiments indicate that no other cardioregulatory nerves are present. Both increases and decreases in heart activity can be produced upon electrical stimulation of nerve VIIIb on each side of the heart. Only one action potential associated with the response of each type could be recorded in each member of the nerve pair. Therefore, we conclude that there are two inhibitory and two acceleratory neurons that arise in the central nervous system to modulate heartbeat activity. The inhibitory effect becomes maximal at a stimulation frequency of 20-30 Hz and the accelerator effect at 30-40 Hz. The aftereffect of acceleratory nerve activity exceeds that of inhibitory nerve activity. When the inhibitor and accelerator are activated simultaneously, the inhibitor dominates. The regulatory nerves interact with neurons in the cardiac ganglion. During inhibition, the number of externally recorded spikes in each ganglionic burst is decreased. The rate and magnitude of the heartbeat are decreased concomitantly. Stimulation of the accelerator enhances electrical activity in the cardiac ganglion at the same time that the heartbeat rate and amplitude are increased.     

The effects of biogenic monoamines and related agonists and antagonists on the isolated,perfused branchial heart of sepia officinalis L. (cephalopoda)

1. The chronotropic and inotropic effects of biogenic monoamines were examined on the isolated and perfused branchial heart of the common cuttlefish Sepia officinalis (L.).2. Adrenaline, noradrenaline and dopamine caused concentration-dependent increases in pressure amplitude, dopamine being 100-fold less potent than adrenaline and noradrenaline. The catecholamines hardly affected frequency.3. Octopamine, histamine and GABA did not influence normal heartbeat.4. Serotonin was either ineffective or produced variable responses, whereby the efficacy of the substance was not graded to the concentrations applied. It is supposed that serotonin is not involved in branchial heart regulation.5. The actions of different adrenergic agonists and antagonists indicate the presence of a myocardial adrenoceptor which closely resembles the α₁-type.     

Mechanism for amine modulation of the neurogenic Limulus heart: evidence for involvement of cAMP

The role of cyclic nucleotides as intracellular second messengers mediating the excitatory chronotropic and inotropic actions of octopamine (OCT) and dopamine (DA) on the neurogenic Limulus heart was investigated. Tissue levels of cAMP, but not cGMP, were significantly increased in isolated cardiac ganglia and cardiac muscle following 10 min exposure to 10(-5) M OCT or 10(-5) M DA. In both tissues, OCT elicited larger increases in cAMP than did DA. Amine-induced cAMP accumulation in the cardiac ganglion and in the cardiac muscle was prevented by the alpha-adrenergic blocker phentolamine. The adenylate cyclase activator forskolin and the phosphodiesterase inhibitor IBMX produced amine-like chronotropic and inotropic effects when applied to the isolated heart preparation. However, the kinetics of the responses differed for the two agents. Additional pharmacological agents (RO-20-1724, papaverine, SQ 20,009, and 8-parachloro-phenylthio cAMP) also had amine-like effects but to a lesser extent. The chronotropic, but not inotropic, effects of OCT and DA were potentiated in the presence of IBMX. These data suggest that a cAMP-dependent mechanism underlies the excitatory effects of the neuromodulators OCT and DA on the Limulus heart.     

Amine modulation of the neurogenic Limulus heart

(1) The biogenic amines octopamine (OCT), dopamine (DA), epinephrine (E), and norepinephrine (NE) cause dose-dependent increases in both the rate and amplitude of contractions of the isolated Limulus heart-cardiac ganglion. Their relative ability to produce this excitation is OCT greater than DA approximately the same as E greater than NE. (2) The excitatory effects of all these amines are antagonized by the alpha-adrenergic blocker phentolamine and the dopaminergic antagonist haloperidol. The beta-adrenergic antagonist dichloroisoproterenol slightly reduces amine excitation, but is also a partial agonist. The beta-adrenergic antagonist propanolol, the alpha-blocker phenoxybenzamine, and the serotonin antagonist metergoline are ineffective. (3) In addition to their excitatory effects, DA and, to a lesser extent, NE initially reduce contraction rate and amplitude. (4) The transient inhibition is eliminated selectively by metergoline and is unaffected by the other antagonists. (5) The amines all increase the frequency of cardiac ganglion electrical bursting activity, whether ganglia are isolated or attached to cardiac muscle. Dopamine and NE also transiently inhibit the cardiac ganglion. (6) The amines do not alter myocardial resting tension, contractility, or membrane potential. (7) These amines appear to exert their modulatory effects on Limulus heart by altering the properties of the neurons which comprise its cardiac ganglion.     

Proctolin affects the activity of the cardiac ganglion, myocardium, and cardioarterial valves in Carcinus maenas hearts

The decapod crustacean heartbeat is initiated by the cardiac ganglion and is regulated by a variety of neuronal and hormonal inputs. In this paper we examine the effects of the peptide hormone proctolin which appears to have multiple sites of action in the shore crab, Carcinus maenas. To examine some of the potential sites of proctolin action we used three heart preparations: in situ intact and open hearts, and isolated hearts. We provide evidence in support of the hypothesis that proctolin affects cardiac activity at many levels. It acts at the cardiac ganglion to modulate burst rate and at the myocardium to alter contractile force. We calculated the relationship between contractility and ganglionic output of in situ hearts as the ratio of ventricular pressure or tension to amplitude of the electromyogram or intracellular excitatory junction potential. Large proctolin-induced changes in this ratio, which could not be accounted for by ganglionic output, membrane potential or input resistance suggest direct action on the myocardium. The greater increases in ventricular pressure than in tension in the in situ hearts may reflect proctolin-induced contraction of the cardioarterial valves. Finally, proctolin can possibly influence heart rate by action on the cardioregulatory nerves of the central nervous system. Accepted: 11 May 1998     

Heartbeat patterns during the postembryonic development of Drosophila melanogaster

Pulsations of the dorsal vessel were recorded in vivo during the whole postembryonic development of D. melanogaster, by means of a newly invented, pulse-light opto-cardiographic method. The young larvae of the 1st and 2nd instars submerged in the feeding medium exhibited extremely high rates of heartbeat, 7Hz at room temperature. These values are among the highest rates of heartbeat ever recorded in the animal kingdom. The fully grown larvae of the 3rd instar showed approximately half of the maximum heartbeat rate (3.5-4Hz), which became stabilized after pupariation to 2.5-2.7Hz.The larval heartbeat was always uni-directional, in the forward-oriented or anterograde direction and it was almost continuous. The slowly disintegrating, old larval heart used to beat at the constant frequency of 2.5-2.7Hz until complete cessation of all cardiac functions in 1-day-old puparium. In spite of the persisting constant heartbeat frequency, the transformation process of the larval heart was associated with successively decreasing amplitude of the systolic contractions and with the prolongation of the resting periods. The newly formed heart of the pupal-adult structure exhibited a qualitatively new pattern of heartbeat activity, which was manifested by periodic reversal of the heartbeat with the faster anterograde and slower retrograde phases. The frequencies of both of these reciprocal cardiac pulsations gradually increased during the advanced pharate adult period, reaching the values of 4-5Hz at the time of adult eclosion. Adult males and females also exhibited a perfect pattern of heartbeat reversal, with still very high rates of the anterograde heartbeat, in the range of 5-6Hz. In addition to the cardiac functions, we have recorded several kinds of extracardiac pulsations, which often interfered severely with the recordings of the heartbeat. There were strong, irregular extracardiac pulsations of a neurogenic nature (somatic muscles, oral armature) and relatively slow extracardiac pulsations of a myogenic nature (intestinal peristaltics, 0.2-0.3Hz). The extracardiac and cardiac pulsations were independent, their functions were not correlated. A possibility of creating new challenges in combination of molecular biology with the functional physiology of the heart have been discussed.     

Electrophysiology of the flounder heart (Platichthys flesus)—the effect of agents which modify transmembrane ion transport

1. A sucrose gap system was used to record action potentials and mechanical responses of flounder heart.2. Diltiazem eliminated mechanical responses and strongly inhibited the action potential plateau while nifedipine only slightly reduced cardiac contractions without significantly changing the action potential.3. Verapamil slightly hyperpolarized flounder heart but was without effect on either the action potential or mechanical activity except at very high concentrations.4. Lanthanum was ineffective at 2 mM on flounder heart, but manganese at 3 mM substantially inhibited electrical and mechanical responses accompanied by a small hyperpolarization. Substitution of manganese for calcium abolished all flounder cardiac activity.5. BAY K 8644 enhanced cardiac force and enhanced the action potential plateau while depolarizing the preparations. Calcium-free salines abolished heart contractions and the action potential plateau while the spike phase persisted.6. Low sodium salines enhanced while sodium-free salines abolished all heart activity as did tetrodotoxin above I μM. Tetrodotoxin abolished the action potential spike leaving only a small plateau phase.7. Substituting lithium for sodium hyperpolarized the heart, enhanced contractions and prolonged the action potential plateau. Ouabain enhanced cardiac activity and depolarized the heart but ferosemide was without effect on either electrical or mechanical activity.8. TEA at 6 mM had a modest positive inotropic effect and negative chronotropic effect on the heart while the action potential plateau phase was enhanced.9. These results indicate that extracellular sodium and calcium are crucial in flounder heart electrogenesis but such a major role for potassium could not be established.     

Localization of neurons, making projections via the postganglionic nerves of the stellate ganglion

Distribution of neurons, forming cardiac nerves of the cat stellate ganglion, has been investigated. The inferior cardiac nerve conducts inotropic influences to the heart. It is formed by the neurons localized in the caudal part of the ganglion. The caudal anastomosis conducts chronotropic influences to the heart. It is formed by the neurons localized in the inferior part of the ganglion and the ventral horn of the spinal nucleus and nucleus intercalatus. Axons of the preganglionic neurons pass through the ganglion and are not interrupted.     

Acceleratory nervous regulation of juvenile myogenic hearts in the isopod crustacean Ligia exotica

We examined regulation of the myogenic heart by two identified cardioacceleratory neurons (CA1, CA2) in early juveniles of the isopod Ligia exotica. Repetitive stimulation of either the CA1 or CA2 axon increased the frequency and plateau amplitude of the action potential and decreased the maximum hyperpolarization of the cardiac muscle. These effects were larger with increasing stimulus frequency. The rate of increase in the frequency caused by CA1 stimulation was significantly larger than that by CA2. No impulse activity of the cardiac ganglion was induced by acceleratory nerve stimulation. The frequency of the muscle activity was decreased by injection of a hyperpolarizing current into the muscle during stimulation of the acceleratory nerve. In a quiescent heart, acceleratory nerve stimulation caused an overall depolarization in the muscle membrane and the amplitude of the depolarization induced by CA1 stimulation was significantly larger than that by CA2. These results suggest that CA1 and CA2 neurons regulate the myogenic heart affecting directly the cardiac muscle; the CA1 neuron produces more potent effects than does the CA2 neuron.     

Heart Activity in the Crayfish Astacus astacus during Early Ontogenesis

Using a non-invasive method of recording of heart activity in crayfish Astacus astacus in early ontogenesis (1–9 months) and analysis of parameters of cycles of laser light cardiogram, it is shown that cardiac contraction rate (CCR) decreases with increases of weight and size of the animals. The range of changes of CCR parameters in air and in water is wider in larger crayfish of the same age, than in crayfish retarding from them in size and weight. This seems to allows the larger crayfish to be better adapt to environmental changes. It is shown that in crayfish, at change of environmental conditions, inotropic parameters of the cardiogram, amplitude of diastole and systole (DA and SA), change more, than chronotropic parameters, duration of diastole and systole (DD and SD). This may indicate that systems of regulation of inotropic parameters of the cardiac activity are the first to become mature in ontogenesis of the crayfish cardiovascular system; later, maturation of system of regulation of chronotropic parameters of the heart activity occurs. This is confirmed by results of experiments on adult crayfish. Analysis of correlations between parameters of cardiogram cycles in crayfish has shown that regardless of crayfish weight, higher correlation coefficient values are revealed between inotropic parameters of the heart activity cycles, than between chronotropic parameters. In larger crayfish, DD values are higher, than SD, whereas in stress, SD is longer than DD. During stress, the highest negative values of the correlation coefficient are revealed between CCR and DA, CCR and SA regardless of in which medium (air, water) the crayfish is placed.     

Role of the neuropeptide CCAP in Drosophila cardiac function

The heartbeat of adult Drosophila melanogaster displays two cardiac phases, the anterograde and retrograde beat, which occur in cyclic alternation. Previous work demonstrated that the abdominal heart becomes segmentally innervated during metamorphosis by peripheral neurons that express crustacean cardioactive peptide (CCAP). CCAP has a cardioacceleratory effect when it is applied in vitro. The role of CCAP in adult cardiac function was studied in intact adult flies using targeted cell ablation and RNA interference (RNAi). Optical detection of heart activity showed that targeted ablation of CCAP neurons selectively altered the anterograde beat, without apparently altering the cyclic cardiac reversal. Normal development of the abdominal heart and of the remainder of cardiac innervation in flies lacking CCAP neurons was confirmed by immunocytochemistry. Thus, in addition to its important role in ecdysis behavior (the behavior used by insects to shed the remains of the old cuticle at the end of the molt), CCAP may control the level of activity of the anterograde cardiac pacemaker in the adult fly. Expression of double stranded CCAP RNA in the CCAP neurons (targeted CCAP RNAi) caused a significant reduction in CCAP expression. However, this reduction was not sufficient to compromise CCAP's function in ecdysis behavior and heartbeat regulation.     

Purinergic regulation of rat heart function in ontogeny

The effect of exogenous ATP and its analogs on heart function was studied in 14–100-day-old rats. Extracellular purines had a positive chronotropic effect on the heart. Intravenous administration of exogenous ATP and its stable analogs induced a dose-dependent increase in heart rate depending on animal age. The analysis of isometric contraction of myocardial strips demonstrated a dose-dependent positive inotropic effect of ATP. The family and subtype of the P2 receptors realizing the positive chronotropic and inotropic effects were identified using selective agonists and blockers. P2X receptors demonstrated the highest sensitivity during early postnatal ontogeny. The age-related pattern of the receptor response to exogenous purines indicated the heterochronic maturation of P2X and P2Y receptors in the myocardium.     

Acceleratory Synapses on Pacemaker Neurons in the Heart Ganglion of a Stomatopod, Squilla oratoria

The pacemaker neurons of the heart ganglion are innervated from the CNS through two pairs of acceleratory nerves. The effect of acceleratory nerve stimulation was examined with intracellular electrodes from the pacemaker cells. The major effects on the pacemaker potential were an increase in the rate of rise of the spontaneous depolarization and in the duration of the plateau. The aftereffect of stimulation could last for minutes. No clear excitatory postsynaptic potential (EPSP) was observed, however. On high frequency stimulation, a small depolarizing response (the initial response) was sometimes observed, but the major postsynaptic event was the following slow depolarization, or the enhancement of the pacemaker potential (the late response). With hyperpolarization the initial response did not significantly change its amplitude, but the late response disappeared, showing that the latter has the property of the local response. The membrane conductance did not increase with acceleratory stimulation. The injection of depolarizing current increased the rate of rise of the spontaneous depolarization, but only slightly in comparison with acceleratory stimulation, and did not increase the burst duration. It is concluded that the acceleratory effect is not mediated by the EPSP but is due to a direct action of the transmitter on the pacemaker membrane.     

Myocardial Depolarizing Response to Glutamate in the Myogenic Heart of the Branchiopod Crustacean Triops longicaudatus

Fine structure of the heart and the effects on the heartbeat of some transmitter candidates in crustacean cardioregulatory system were examined in the myogenic heart of the branchiopod crustacean Triops longicaudatus. Electron microscopy revealed that, in each myocardial cell, myofibrils are confined in the part facing the epicardium and intercalated disks are present between the myofibrillar regions of adjacent myocardial cells. No neural elements were found in the heart, suggesting lack of extrinsic cardioregulatory nerves from the central nervous system. Gamma aminobutyric acid and acetylcholine produced no detect-able changes in the myogenic activity of the heart at concentrations up to 10(-3) M, respectively. Glutamate induced a depolarizing membrane response in the cardiac muscle with a threshold concentration of approximately 1x10(-5) M. The amplitude of the depolarizing response was concetration-dependent and saturated at approximately 1x10(-4) M. The myogenic activity of the heart increased in frequency with glutamate of less than approximately 3x10(-5) M. With higher dose of glutamate, action potential adaptation occurred in the cardiac muscle and the heart exhibited a systolic arrest.