Effect of He-Ne laser irradiation on the functional activity of smooth muscle cells in the portal vein]

Irradiation of the rat portal vein's fragments with the He-Ne laser for 3, 5 and 10 minutes reduced the fragments tone by half. Frequency of phasic and tonic contractions did not change, their amplitude, however, increased by neatly 40% as compared with the initial level. The NO synthase blocker N-nitro-L-arginine administered prior to the irradiation had no effect on the above parameters. The data obtained suggest that the decrease of the vessel tone is due to production of the EDRF and cGMP. The increase in the amplitude of phasic and tonic contractions of the vein's smooth muscle cells is associated with an increased Ca++ entry in each contraction cycle.     

Circadian inputs influence the performance of a spiking, movement-sensitive neuron in the visual system of the blowfly.

Long-term extracellular recordings from a spiking, movement-sensitive giant neuron (H1) in the third optic ganglion of the blowfly Calliphora vicina (L.) revealed periodic endogenous sensitivity fluctuations. The sensitivity changes showed properties typical of an endogenous circadian rhythm. This was true for the responses in reaction to intensity changes of visual patterns as well as for the responses elicited by pattern movement. For these two types of stimuli, the circadian fluctuations were comparable, but the envelope in the case of responses to movement was more robust. A circadian fluctuation in responses to movement is, therefore, present at the level of single elementary movement detectors. The tonic activity of the neuron was also shown to be under circadian control. In constant darkness (DD) the fluctuation was circadian, whereas in constant light it was not. The subjective light-dark (LD) transitions in the tonic activity in DD closely followed the LD transitions in the holding cages initially; that is, there was low activity at night and high activity during the daytime. The sensitivity fluctuations in response to visual stimuli led the tonic spike activity fluctuations by several hours.     

Effects of pressure stimulation of the body surface on posture and vestibulospinal reflexes

The effects of pressure stimulation of the body surface on postural activities as well as on the response gain of limb extensors to natural stimulation of labyrinth receptors were investigated in intact, as well as in decerebrate cats. In intact, unanesthetized cats, slight pressure applied symmetrically to the body surface at the chest level decreased the tonic activity of the axial (neck) and limb extensor musculature, as well as the proprioceptive reflexes induced by passive flexion of the limbs. The positive supporting reaction caused by pressure applied to the pad of the foot was also depressed. If the cats were suspended in the air by their nape, slight pressure applied to the upper part of the body greatly reduced the tonic contraction of the forelimb extensors to linear acceleration after downward movement of the animal, a response which can be attributed to stimulation of macular receptors located in the sacculus. Moreover, the prominent myotatic reflexes which occurred in all four limbs as soon as the animal touched the floor were greatly depressed, as shown by the fact that the forelimbs displayed only a slight tonic contraction of the extensor musculature during landing, while the hindlimbs collapsed under the weight of the body. In precollicular decerebrate cats there was a good postural activity in all four limbs. Moreover, the multiunit EMG activity of the medial head of the triceps brachii responded to roll tilt of the animal (at 0.15 Hz, +/- 10 degrees) leading to selective stimulation of labyrinth receptors. These responses, characterized by an increased EMG activity during side-down tilt and a decreased activity during side-up tilt, were related to animal position and not to velocity of animal displacement, and are thus attributable to stimulation of macular, utricular receptors. Slight pressure applied to the chest greatly decreased not only the postural activity of the limbs, but also the amplitude of EMG modulation and then the gain in the first harmonic component of the multiunit EMG responses of the triceps brachii to animal tilt. This reduced gain was due, in particular, to a reduced number of motor units being recruited during labyrinth stimulation, although a reduced modulation of firing rate of the active motor units should not be ruled out. However, no changes in the phase angle of the responses were observed.(ABSTRACT TRUNCATED AT 400 WORDS)     

Voltage dependent activation of tonic contraction in cardiac myocytes.

Contractions of isolated single myocytes of guinea pig heart stimulated by rectangular depolarizing pulses consist of a phasic component and a voltage dependent tonic component. In this study we analyzed the mechanism of activation of the graded, sustained contractions elicited by slow ramp depolarization and their relation to the components of contractions elicited by rectangular depolarizing pulses. Experiments were performed at 37 degrees C in ventricular myocytes of guinea pig heart. Voltage-clamped myocytes were stimulated by the pulses from the holding potential of -40 to +5 mV or by ramp depolarization shifting voltage within this range within 6 s. [Ca2+]i was monitored as fluorescence of Indo 1-AM and contractions were recorded with the TV edge-tracking system. Myocytes responded to the ramp depolarization between -25 and -6 mV by the slow, sustained increase in [Ca2+]i and shortening, the maximal amplitude of which was in each cell similar to that of the tonic component of Ca2+ transient and contraction. The contractile responses to ramp depolarization were blocked by 200 microM ryanodine and Ca2+-free solution, but were not blocked by 20 microM nifedipine or 100-200 microM Cd2+ and potentiated by 5 mM Ni2+. The responses to ramp depolarization were with this respect similar to the tonic but not to the phasic component of contraction: both components were blocked by 200 microM ryanodine, and were not blocked by Cd2+ or Ni2+ despite complete inhibition of the phasic Ca2+ current. However, the phasic component but not the tonic component of contraction in cells superfused with Ni2+ was inhibited by nifedipine. Both components of contraction were inhibited by Ca2+-free solution superfused 15 s prior to stimulation. CONCLUSIONS: In myocytes of guinea pig heart the contractile response to ramp depolarization is equivalent to the tonic component of contraction. It is activated by Ca2+ released from the sarcoplasmic reticulum by the ryanodine receptors. Their activation and inactivation is voltage dependent and it does not depend on the Ca2+ influx by the Ca2+ channels or reverse mode Na+/Ca2+ exchange, however, it may depend on Ca2+ influx by some other, not yet defined route.     

Respiratory-related bronchial rhythmic constrictions in the dog with extracorporeal circulation.

Respiratory-related bronchial rhythmic contraction was quantitatively analyzed in eight paralyzed dogs. The caliber of the fifth-generation bronchus was continuously measured as the pressure (Pbr) of a balloon-tipped catheter under the condition of complete immobilization due to extracorporeal oxygenation. Pbr changed rhythmically in synchrony with phrenic nerve activity (PNA) bursts. Rhythmic bronchial constriction started at 1.4 +/- 0.49 (SD) s after onset of PNA, reached a maximum level at 2.8 +/- 1.6 s after termination of PNA, and then decreased exponentially with a time constant of 6.9 +/- 2.5 s. When the respiratory rate of dogs increased at hypercapnia, the various bronchial contractions fused to behave like a tonic contraction. The rhythmic component of this contraction was separated and quantitatively analyzed. Each rhythmic Pbr amplitude linearly increased with increases in PNA amplitude, whereas the end-expiratory Pbr level was not significantly changed. Bilateral efferent nerve transection did not decrease the end-expiratory Pbr level. In response to electric stimulation of efferent nerve fibers, the bronchus did not maintain tonic contraction. We concluded that vagally mediated commands contract bronchial smooth muscle only intermittently and that most of bronchial resting tension may thus be attributed to the summation of rhythmic contractions.     

Potential-dependent calcium channels in rabbit jejunum

Potential-dependent calcium channels have been studied in the isolated rabbit jejunum. A biphasic response was observed, a transient and rapid contraction followed by partial relaxation and a sustained contraction attaining a plateau state. These are similar to the phasic and tonic responses observed in the isolated smooth muscles of other species. Both the responses are susceptible to blockade by the calcium antagonists bepridil, diltiazem, nifedipine, PN 200-110 (isradipine), and verapamil. Two calcium pools or the presence of two channels affecting the two responses are proposed.     

Seasonal changes in the effects of arginine vasotocin and stretch on Anolis uterine contractions in vitro

We determined the effects of acute stretch on spontaneous and arginine vasotocin (AVT)-driven contractions of the Anolis carolinensis uterus in vitro. Whole uteri from reproductively inactive females (October) were placed in a bath of oxygenated 32 degrees C Anolis "Ringer's." Two initial tensions were utilized, 1.5 g or 15 g, the latter being an estimate of the tension on the wall of a uterine compartment. Uteri were then exposed to either saline or AVT (50 ng/ml), and spontaneous or AVT-driven contractions were recorded for 20 min with the use of a strain gauge and physiograph. A similar experiment was performed on uteri from reproductively active females in the summer (June). Our results indicate that the effects of acute stretch and AVT on uterine contractility were qualitatively similar in summer and fall. That is, AVT induced a tonic contraction; stretch decreased the duration of the tonic contraction; the saline-treated uteri exhibited spontaneous rhythmic contractions; AVT increased the amplitude of the rhythmic contractions, but only at the lower tension; there were no effects of AVT on the timing (contraction interval, duration, rest interval) of the rhythmic contractions; and stretch increased the frequency of the rhythmic contractions. Season greatly influenced the magnitude of these contractile phenomena. Uteri tested during the breeding season exhibited greater distensibility, an increase in the amplitude and duration of the AVT-driven tonic contraction, and an increase in the frequency of both spontaneous and AVT-driven rhythmic contractions because of a decrease in both contraction duration and rest interval.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enteric opioid neurons modulate the basal tone of the isolated puppy ileum

We studied the role of enteric opioid neurons in the spontaneous motility of the longitudinal muscle in the isolated puppy ileum. Regular fluctuations in tone that rose above and returned to the basal level occurred at an interval of 4.7 +/- 0.3 min. Naloxone (10(-8) and 10(-7) M) reduced the spontaneous tonic contraction by 42.6 +/- 11.6% (p less than 0.02) and 77.0 +/- 3.6% (p less than 0.001), respectively. Tetrodotoxin (3.1 X 10(-7) M) and atropine (10(-7) M) terminated the fluctuations. Met- and Leu-enkephalins (10(-9)-10(-8) M) caused tonic contraction which was abolished by tetrodotoxin and atropine. The contractile response produced by transmural electrical stimulation was reduced by naloxone (10(-7) M). This response was also abolished by atropine and tetrodotoxin. These results suggest that enteric opioid neurons are spontaneously active and might operate, at least in part, to raise the basal tone of the longitudinal muscle in the puppy ileum through a cholinergic excitatory mechanism.     

Effects of the membrane potential level on serotonin-induced contraction of the pulmonary artery smooth muscle in rabbits]

The effects of changes in membrane potential level on the electrical and contractile responses induced by serotonin (10(-6) mol/l) were investigated in muscle strips from rabbit main pulmonary artery using sucrose-gap technique. In spite of the fact that serotonin-induced depolarization did not exceed the threshold level for development of contraction, it was followed by a strong tonic contraction. Nearly a half of this contraction could be relaxed by an electrotonic hyperpolarization of the membrane. A week preliminary depolarization of the muscle cells resulted in an increase while a strong depolarization--in dramatic decrease of serotonin-induced contraction. Nifedipine effectively blocked potassium-induced, but not serotonin induced contraction. We suggest that in addition to voltage-operated and receptor operated Ca channels in vascular smooth muscle cell membrane there is a separate class of nifedipine-insensitive Ca channels operated by both serotonin receptor and membrane potential.     

Fluctuations in tension during contraction of single muscle fibers.

We have searched for fluctuations in the steady-state tension developed by stimulated single muscle fibers. Such tension "noise" is expected to be present as a result of the statistical fluctuations in the number and/or state of myosin cross-bridges interacting with thin filament sites at any time. A sensitive electro-optical tension transducer capable of resolving the expected fluctuations in magnitude and frequency was constructed to search for the fluctuations. The noise was analyzed by computing the power spectra and amplitude of stochastic fluctuations in the photomultiplier counting rate, which was made proportional to muscle force. The optical system and electronic instrumentation together with the minicomputer software are described. Tensions were measured in single skinned glycerinated rabbit psoas muscle fibers in rigor and during contraction and relaxation. The results indicate the presence of fluctuations in contracting muscles and a complete absence of tension noise in eith rigor or relaxation. Also, a numerical method was developed to simulate the power spectra and amplitude of fluctuations, given the rate constants for association and dissociation of the cross-bridges and actin. The simulated power spectra and the frequency distributions observed experimentally are similar.     

Effects of agonists and antagonists of rhyanodine receptors on potassium contractures in twitch and tonic frog skeletal muscle fibers

A comparative analysis of the effects of the concentrations of Ca2+ in external medium and the inhibitor (dantrolene) and activator (4-chloro-m-cresol) of rhyanodine-sensitive Ca2+ channels of carcoplasmic reticulum on the characteristics of potassium contracture in frog twitch and tonic skeletal muscles has been performed. It was shown that the duration of contracture in tonic muscles is not restricted by the presence of Ca2+, as distinct from twitch muscles. Dandrolene does not practically affect the contractile responses of tonic fibres, and the concentration of cresol eliciting the contracture for tonic fibres is substantially higher (1 mM) than for twitch fibers (0.25 mM). In twitch fibers, the potassium contracture activated in the presence of cresol is comparable in amplitude and dynamics with the contracture under control conditions, and in tonic fibers a summing of responses without relaxation after the washing of excessive potassium is observed. This suggests that, in twitch fibers, the influx of Ca2+ can directly create the concentration sufficient for the maintenance of contraction, and in tonic fibers its involvement is mediated through the Ca(2+)-dependent activation of the beta-isoform of rhyanodine-sensitive channels.     

Endothelium-independent and -dependent contractions induced by endothelin-1 in canine basilar arteries

Endothelium-dependence of contractile responses to endothelin-1 was examined in isolated canine basilar arteries. Within 2 hrs after mounting tissue preparations, endothelin-1 (10(-9) M) caused a monophasic tonic contraction that developed very slowly and was sustained in intact and endothelium-removed arteries. More than 5 hrs after tissue mounting, endothelin-1 (10(-9) M) caused a biphasic contraction consisting of phasic and tonic components in intact arteries, and caused a monophasic tonic contraction in endothelium-removed arteries. This phasic component was significantly decreased by aspirin (5 x 10(-5) M,), OKY-046 (10(-5) M) (a TXA2 synthetase inhibitor) and ONO-3708 (10(-8) M) (a TXA2 antagonist). The present experiments demonstrate that endothelin-1 causes an endothelium-independent tonic contraction and an endothelium-dependent phasic contraction in canine basilar arteries, and suggest that TXA2 plays a role as an endothelium-derived contracting factor.     

Ultradian Rhythms in Arousal-The Problem of Masking

Studies utilizing widely different experimental techniques provided evidence that there are spontaneous ultradian cycles in arousal during the waking state. These comprised of cyclic fluctuations between increased and decreased sleep propensity with a periodicity of about 1.5 hr. Being of relatively low amplitude, these cycles are vulnerable to masking effects by a variety of experimental conditions. Masking can be exerted by varying the tonic level of arousal, by coexisting slow ultradian components which are particularly prominent during the second half of the day, or by some specific experimental conditions. Furthermore, increased sleepiness was shown to enhance the slow ultradian components and suppress the 1.5-hr cycles in EEG indices of arousal on the one hand, and to emphasize the 1.5-hr cycles in motor activity and reaction time performance on the other hand. Much more attention should be paid to the problem of masking of ultradian cycles in arousal. Recognizing the sources and reasons for masking will ad vance our knowledge of the characteristics of these cycles and their function.     

Effect of chronic intermittent exposure to AM radiofrequency field on responses to various types of noxious stimuli in growing rats

There are several reports of altered pain sensation after exposure (from a few minutes to hours in single or repeated doses for 2-3 weeks) to electromagnetic fields (EMF) in adults. The commonly utilized noxious stimulus is radiant heat. The nociceptive responses are known to be influenced by characteristics of stimulus, organism, and environment. We studied the pattern of nociceptive responses to various noxious stimuli in growing rats exposed to radiofrequency field (73.5 MHz amplitude modulated, 16 Hz power density 1.33 mw/cm(2), SAR = 0.4 w/kg) for 45 d (2 h/d). Threshold current for stimulation of nociceptive afferents to mediate motor response of tail (TF), vocalization during stimulus (VD), and vocalization after discharge (VA); the withdrawal latency of tail (TFL) and hind paw (HPL) to thermal noxious stimulus and tonic pain responses were recorded in every rat. The TFL was not affected, HPL was decreased (p < 0.01), and the thresholds of TF and VD were not affected, while, that of VA was significantly decreased. The tonic pain rating was decreased (p < 0.01). A decrease in the threshold of VA (p < 0.01) is indicative of an increase in the emotional component of the response to the phasic pain, whereas a decrease in the pain rating indicates analgesia in response to the tonic pain. The results of our study suggest that chronic (45 d), intermittent (2 h/d) amplitude modulated RF field exposure to the peripubertal rat increases the emotional component of phasic pain over a basal eaualgesic state, while late response to tonic pain is decreased. The data suggest that amplitude modulated RF field differentially affects the mechanisms involved in the processing of various noxious stimuli.     

Comparative actions of the neuropeptides leucopyrokinin and periplanetin CCI on the visceral muscle systems of the cockroaches Leucophaea maderae and Periplaneta americana

1. The effects of two structurally-related peptides, leucopyrokinin (LPK) and periplanetin CC-I (CCI), on contractile activities of visceral muscle systems were compared in the two cockroaches from which these peptides were originally isolated.2. LPK elicited consistent proctolin-like responses on the hindgut, foregut, oviduct and heart of the Madeira cockroach, Leucophaea maderae, with increases in both amplitude and frequency of contraction. CCI, on the other hand, elicited a mostly tonic response on these tissues.3. For the American cockroach, Periplaneta americana, the responses elicited by LPK and CCI were tonic in nature.4. With the exception of the response of the L. maderae hindgut and heart to LPK, threshold levels for either LPK or CCI on all other tissues of both roaches were considerably higher (10–100 times greater) than those for proctolin on the same tissues.5. The maximum response to any concentration of LPK or CCI on the foregut and oviduct of L. maderae and that on the foregut and hindgut of P. americana never reached more than 60% of the maximum contraction achieved with proctolin.     

cAMP dependence of Ca2+ entry during agonist-induced contractions of the uterine smooth muscles

Possible involvement of cAMP-dependent mechanisms in the development of both phasic and tonic contractions induced by oxytocin — OT (25 nM and 25 µM, respectively), as well as of KCl-induced contracture, was studied on the myometrium of estradiol-dominated rats using the myometrial strips with suppressed spontaneous mechanical activity. The intracellular cAMP level was modulated by furosemide that had been previously shown to decrease cAMP content in the rat myometrium tissue. When added to the medium in the pulse mode together with 25 nM OT, furosemide (0.02 mM) increased contraction amplitude by 224%, whereas higher, 0.2 and 20 mM, furosemide concentrations suppressed the response by 286% or totally removed it, respectively. Being present in the bath permanently, 0.2 mM furosemide progressively decreased the amplitude of OT-induced phasic contractions. Under such conditions, 0.02 mM furosemide exerted biphasic effect on the responses, so that the initial enhancement was replaced by the progressive inhibition. Dibutyryl-cAMP (dbcAMP) at a proper concentration restored the responsiveness of the tissue to OT in the presence of furosemide in the saturating concentration. Contractile responses induced by 25 µM OT comprised both phasic and tonic components. In a Ca²⁺-free medium, the OT-induced contractions seemed to be associated with Ca²⁺ release from intracellular stores. Permanent presence of furosemide in the CaCl₂-containing medium inhibited OT-induced responses in the same manner as omission of Ca²⁺ from the medium, i.e., furosemide did not affect the responses caused by Ca²⁺ release but inhibited those mediated via acceleration of the Ca²⁺ influx. The furosemide-sensitive component of responses to OT was combined with a persistent contraction caused by KCl depolarization; there was a moderate decrease in amplitude of the KCl-induced contracture due to furosemide action. The decrease could be prevented by dbcAMP addition. It is suggested that both voltage-gated and receptor-operated Ca²⁺ entries induced by OT are regulated by cAMP-dependent protein kinases, while Ca²⁺ extrusion into the extracellular space does not depend on the intracellular cAMP.Neirofiziologiya/Neurophysiology, Vol. 26, No. 1, pp. 54–60, January–February, 1994.     

Voltage responses to tones of outer hair cells in the basal turn of the guinea-pig cochlea: significance for electromotility and desensitization.

Voltage responses were recorded from outer hair cells (OHCS) in the basal coil of the guinea-pig cochlea in response to tones at frequencies above the characteristic frequency (CF) presented together with a 100 Hz tone at 80 dB or 85 dB sound pressure level (SPL). The amplitude and polarity of voltage responses to a 100 Hz, 85 dB SPL tone were altered when presented together with tones at frequencies above CF according to the frequency and level of the high-frequency tone, OHC phasic (ac) (greater than 500 microV) but not tonic (dc) voltage responses were elicited by the high-frequency tone. Thus the responses of OHCS to low-frequency tones can be altered when presented together with a high-frequency tone without an apparent dc change in membrane potential. Recordings were made from an OHC during cochlear desensitization through exposure to an intense tone. The maximum voltage response to high-level low-frequency tones remained unchanged, although the OHC response to high-frequency tones became less sensitive to low-level stimuli and more linear as a function of level. It is suggested that desensitization is associated with a change in the mechanical properties of the cochlea, possibly associated with the OHCS themselves, and not with inactivation of the transducer channels. The amplitude of the OHC ac voltage response was measured at neural threshold, and the consequences of these measurements on hair cell electromotility are considered.     

Uterine motility in the reptile Anolis carolinensis: interactive effects of tension, prostaglandins, calcium, and vasotocin

Uteri of Anolis carolinensis exhibited spontaneous rhythmic contractions in vitro. Addition of arginine vasotocin (AVT) caused an immediate, strong, tonic contraction followed by rhythmic contractions with the same frequency as spontaneous contractions but of a greater amplitude. At low tension (1.5 g) the AVT-induced tonic contraction was blocked by low dose of indomethacin, suggesting that it is influenced by calcium rather than prostaglandins (PGs). An increase in tension (from 1.5 to 15 g) reduced the duration of the AVT-induced tonic contraction; this stretch-induced decrease was also blocked by indomethacin. Stretch also decreased the duration of the rhythmic contractions, but this stretch effect was not inhibited by indomethacin. The rest interval between rhythmic contractions was decreased by PGF2alpha and PGE2, and indomethacin or stretch blocked these PG effects. Indomethacin, AVT, or stretch alone did not affect PGF2alpha secretion from AVT-treated uteri. Stretch also reduced PGF2alpha secretion from AVT-treated uteri, an effect inhibited by indomethacin.     

Influence of ryanodine receptor agonist and antagonist on development of potassium contracture in phasic (twitch) and tonic fibers of frog skeletal muscle

We compared the influence of external calcium and the inhibitor (dantrolene) and activator (4-chloro-m-cresol) of ryanodine-sensitive Ca channels of the sarcoplasmic reticulum on the characteristics of potassium contracture in phasic and tonic frog skeletal muscle fibers. The duration of contracture in tonic fibers, as contrasted to the phasic ones, is not limited by the presence of Ca²⁺. The tonic contractile response is virtually indifferent to dantrolene and is much less sensitive to chlorocresol than the phasic one (1 mM vs. 0.25 mM). In phasic fibers, the K⁺ contracture on the chlorocresol background is quite similar in amplitude and dynamics to that in control, whereas tonic fibers exhibit response summation without relaxation upon removal of excessive K⁺. One can suggest that in phasic fibers the Ca²⁺ influx can directly create a level sufficient to sustain contraction, while in tonic fibers its effect is mediated by Ca-dependent activation of the beta isoform of the ryanodine-sensitive channel.     

The effects of H2O2 on electromechanical activity of the ileum longitudinal muscle

The effects of H2O2 on electrical and mechanical activity of the longitudinal layer from the guinea-pig ileum were studied using sucrose-gap technique and the influence of H2O2 on ionic current was investigated in single smooth muscle cells by the patch-clamp method. In most of the preparations tested, the spontaneous activity observed was composed of slow waves with superimposed action potentials (APs). Both were resistant to tetrodotoxin and atropine. H2O2 (1 mmol/l) evoked sustained 3-5 mV membrane depolarisation, doubled the amplitude of the slow waves and increased their frequency, augmented the APs and reduced their splitting. These changes were accompanied with significant contraction, which had an amplitude comparable to that of the tonic component of 50 mmol/l K+-induced contraction. Calcium-free solution caused membrane depolarisation, reduction of the slow wave amplitude and frequency, disappearance of APs and decreased the mechanical tension of the preparations. Application of H2O2 (1 mmol/l) into the zero-calcium bath solution recovered the APs, which was accompanied by a low amplitude contraction. H2O2 (up to 1 mmol/l) increased the L-type calcium current (I(Ca)) both under conventional whole-cell patch-clamp configuration and under amphotericin-perforated patches by 16 +/- 3%. These data demonstrated that contractile response of the ileum longitudinal smooth muscle preparation evoked by H2O2 was mainly due to the enhanced electrical activity.