The effects of intracellular and extracellular alkalinization on contractions of the isolated rat uterus

The effects of changing pH on a spontaneously active smooth muscle, the myometrium, is examined. We show, for the first time in any smooth muscle, that the frequency of contraction is greatly increased when intracellular pH is raised. Three weak bases, trimethylamine, diethylamine and ammonium, were used to raise intracellular pH (pH_i), at constant external pH, in isolated uteri of pregnant and non-pregnant rats. Each base increased spontaneous uterine contractile activity, particularly by raising the frequency, in a concentration-dependent manner. At the highest concentrations (40–50 mM) frequency was so increased that a maintained contraction resulted. Intracellular alkalinization during a high-K-maintained uterine contraction produced a small, but significant, fall in force. When external pH was increased, the results were greatly influenced by gestational state; in uteri from non-pregnant animals there was no effect whereas uteri from pregnant rats were found to be extremely sensitive to a raised external pH above 7.4; spontaneous contractions were reduced. In pregnant uteri, when both internal and external pH were elevated, spontaneous contractions were immediately reduced, thus the effects of external pH predominated. These findings may have significance in labour.     

Submaximal-exercise-induced impairment of human muscle to develop and maintain force at low frequencies of electrical stimulation

The aim of this study was to test the hypothesis that low intensity exercise-induced low frequency fatigue is caused by failure of excitation-contraction coupling. Changes in knee extension torque at 5, 10, 15, 20 and 50 Hz electrical stimulation of quadriceps muscle in ten healthy, young, male subjects were recorded during 20-min voluntary exercise followed by 60-min recovery. In seven of the ten subjects, changes in torque during 3 min of 10-Hz stimulation were recorded 2 min and 20 min after 20 min voluntary exercise. Exercise was performed at 30% of maximal voluntary contraction with a contraction plus relaxation period of 6 plus 4 s. Torque at 5, 10, 15, 20 and 50-Hz stimulation at the end of exercise was reduced to mean 91.0 (SEM 5.4)%, 68.7 (SEM 5.4)%, 67.2 (SEM 3.9)%, 66.5 (SEM 4.5)% and 74.7 (SEM 4.3)% of control values, respectively. During the first 30 s of the 3 min 10-Hz stimulation, torque was reduced in exercised muscle and increased in nonfatigued muscle. The reduction in torque was more marked 20 min after exercise than after 2 min. In conclusion, the pattern of depression and recovery of muscle force observed was in agreement with the hypothesis that the main cause of low intensity exercise-induced low frequency fatigue is an impairment of excitation-contraction coupling.     

Effects of different frequencies of transcutaneous electrical nerve stimulation on venous vascular reactivity

Transcutaneous electrical nerve stimulation (TENS) is a type of therapy used primarily for analgesia, but also presents changes in the cardiovascular system responses; its effects are dependent upon application parameters. Alterations to the cardiovascular system suggest that TENS may modify venous vascular response. The objective of this study was to evaluate the effects of TENS at different frequencies (10 and 100 Hz) on venous vascular reactivity in healthy subjects. Twenty-nine healthy male volunteers were randomized into three groups: placebo (n=10), low-frequency TENS (10 Hz, n=9) and high-frequency TENS (100 Hz, n=10). TENS was applied for 30 min in the nervous plexus trajectory from the superior member (from cervical to dorsal region of the fist) at low (10 Hz/200 μs) and high frequency (100 Hz/200 μs) with its intensity adjusted below the motor threshold and intensified every 5 min, intending to avoid accommodation. Venous vascular reactivity in response to phenylephrine, acetylcholine (endothelium-dependent) and sodium nitroprusside (endothelium-independent) was assessed by the dorsal hand vein technique. The phenylephrine effective dose to achieve 70% vasoconstriction was reduced 53% (P<0.01) using low-frequency TENS (10 Hz), while in high-frequency stimulation (100 Hz), a 47% increased dose was needed (P<0.01). The endothelium-dependent (acetylcholine) and independent (sodium nitroprusside) responses were not modified by TENS, which modifies venous responsiveness, and increases the low-frequency sensitivity of α1-adrenergic receptors and shows high-frequency opposite effects. These changes represent an important vascular effect caused by TENS with implications for hemodynamics, inflammation and analgesia.     

一氧化氮在休克大鼠离体淋巴管对P物质反应性中的作用

目的: 应用离体淋巴管灌流技术,观察一氧化氮(NO)在失血性休克(HS)大鼠离体淋巴管对P物质(SP)反应性双相变化中的作用。方法: Wistar雄性大鼠随机分为对照组(仅手术)和休克组(复制HS模型后分为shock 0.5 h、shock 2 h组)。在相应时点分离胸导管,制备淋巴管条,3 cmH₂O跨壁压下行离体灌流,应用一氧化氮合酶(NOS)工具药分别孵育shock 0.5 h和shock 2 h的淋巴管。分别给予从低到高浓度的SP,测量淋巴管收缩末期口径、舒张末期口径、收缩频率(CF)和被动管径,计算收缩幅度(CA)、泵流分数(FPF)和紧张指数(TI),以给予SP前后淋巴管的CF、TI、CA和FPF的差值ΔCF、ΔTI、ΔCA和ΔFPF评价淋巴管对SP的反应性。结果: NO供体L-Arg可显著降低shock 0.5 h淋巴管对多个SP浓度点的ΔCF、ΔTI与ΔFPF;可溶性鸟苷酸环化酶抑制剂ODQ可显著抑制L-Arg的作用,在某些SP浓度点上,使ΔCF、ΔTI和ΔFPF显著高于shock 0.5 h+L-Arg组,ΔCF和ΔFPF高于对照组水平。NOS抑制剂L-NAME可提高shock 2 h淋巴管对多个SP浓度点的ΔCF、ΔTI与ΔFPF,且高于对照组水平;shock 2 h淋巴管与L-NAME和磷酸二酯酶抑制剂氨茶碱(AP)同时孵育后,在SP为1×10^-8 mol/L和3×10^-8 mol/L时,AP显著抑制了L-NAME的作用,使ΔCF、ΔTI与ΔFPF明显降低。结论: NO参与了休克淋巴管反应性的双相调节,其机制可能是通过环鸟苷酸实现的。     

Effects of chronic diabetes mellitus on the electrical and contractile activities,45Ca2+ transport,fatty acid profiles and ultrastructure of isolated rat ventricular myocytes

The effects of chronic experimental diabetes on electrophysiological properties, contractile behavior,⁴⁵Ca²⁺ transport, fatty acid profiles and ultrastructural characteristics were studied in enzymatically dissociated ventricular myocytes. Diabetes was induced in rats by streptozotocin administration and animals were killed 8–10 weeks later. Myocytes from diabetic rats exhibited electrical behavior similar to that of myocytes from control rats, but their contractile properties were altered. Their sensitivity of the twitch contractions to various positive and negative inotropic agents (isoproterenol, norepinephrine, phenylephrine, acetylcholine, ouabain and veratridine) was greatly diminished. However, a part of the contractile response (the tonic, sustained contractions) were increased in the diabetic myocytes, indicating that the changes are not caused by a decreased sensitivity of myofilaments. Furthermore, the diabetic myocytes exhibited also significant decrease in total Ca²⁺ content. The fatty acid profile in the diabetic group was changed mainly in that there were slightly elevated levels of docosahexaenoic acid and diminished levels of palmitic acid. The ultrastructure of the diabetic myocytes was affected only slightly. These investigations offer for the first time a comprehensive picture of changes related to diabetic cardiomyopathy as they occur at the level of cardiomyocytes.     

Suppression of VMH-lesion induced reactivity and aggressiveness by electrical stimulation ventral to the anterior septum in the rat

Animals made vicious with bilateral ventromedial hypothalamic lesions had bipolar electrodes implanted unilaterally ventral to the anterior septum just lateral to the diagonal band of Broca or in the lateral septum. Four days later, the animals' reactivity and aggressiveness was evaluated 5 min before, during, and 5 min following 30 sec of stimulation at 20 μA (60 Hz, sine wave). Stimulation of the region ventral to the septum or the lateral septum suppressed reactivity and aggressiveness by almost 70% compared to pre- and poststimulation levels. Stimulated control animals with electrodes in the accumbens nucleus, the diagonal band of Broca or adjacent to the medial septum did not behave differently than unstimulated control animals. Further tests with stimulation of the region ventral to the anterior septum at the 20 μA level showed that the stimulation did not produce either self-stimulation or disruption of ongoing eating. Recordings of electrical activity following the stimulation showed afterdischarge in only one animal. These results are congruent with evidence from lesion studies that the region ventral to the anterior septum as well as lateral septum normally acts to suppress reactivity and aggressiveness in the rat.     

Family history of hypertension,exercise training,and reactivity to stress in rats

In this study we sought to assess the role of exercise training on blood pressure (BP) reactivity to tailshock stress in rats with varying family histories of hypertension. Exercise training consisted of swimming 90 min per day in isothermic water for either 2, 6, or 10 months, beginning at 2 months of age. Control subjects were age-matched and did not exercise daily. Rats with either zero (Wistar-Kyoto), 1 (borderline hypertensive), or 2 (spontaneously hypertensive) hypertensive parents were studied. At the appropriate age, femoral artery catheters were implanted and rats were studied at rest and in response to a 20-min stress session. Exercise training reduced basal BP, especially in rats with a positive family history that were exercised for the longest duration. Reactivity to stress was actually significantly enhanced in trained rats. Thus, these data do not support the reactivity hypothesis, but suggest several reasons why the literature has been so inconsistent. The discussion emphasizes the importance of basal, rather than phasic, BP responses resulting from exercise training. Research for this article was supported by National Institutes of Health (NIH) Grant No. HL19680 to James E. Lawler and NIH Grant No. HL34878 to Ronald H. Cox     

Discharge properties of identified cochlear nucleus neurons and auditory nerve fibers in response to repetitive electrical stimulation of the auditory nerve

Using the in vitro isolated whole brain preparation of the guinea pig maintained at 29°C, we intracellularly recorded and stained cochlear nucleus (CN) neurons and auditory nerve (AN) fibers. Discharge properties of CN cells and AN axons were tested in response to 50-ms trains of electrical pulses delivered to the AN at rates ranging from 100 to 1000 pulses per second (pps). At low stimulation rates (200–300 pps), the discharges of AN fibers and a large proportion of principal cells (bushy, octopus, stellate) in the ventral cochlear nucleus (VCN) followed with high probability each pulse in the train, resulting in synchronization of discharges within large populations of AN fibers and CN cells. In contrast, at high stimulation rates (500 pps and higher), AN fibers and many VCN cells exhibited "primary-like", "onset" and some other discharge patterns resembling those produced by natural sound stimuli. Unlike cells in the VCN, principal cells (pyramidal, giant) of the dorsal CN did not follow the stimulating pulses even at low rates. Instead, they often showed "pauser" and "build-up" patterns of activity, characteristic for these cells in conditions of normal hearing. We hypothesize that, at low stimulation rates, the response behavior of AN fibers and VCN cells is different from the patterns of neuronal activity related to normal auditory processing, whereas high stimulation rates produce more physiologically meaningful discharge patterns. The observed differences in discharge properties of AN fibers and CN cells at different stimulation rates can contribute to significant advantages of high- versus low-rate electrical stimulation of the AN used for coding sounds in modern cochlear implants.     

The response to ether anesthesia and to electric stimulation of glycolytic metabolites in a red and a white muscle of the rat

Summary Since ether anesthesia lowered ATP by 25% in red, but not in white muscle, and only when the spinal neurones were intact, we suggested that small or intermediate muscle units were activated under ether anesthesia [8].In order to prove this postulate, some glycolytic metabolites, known to rise under muscular activation, are studied in the white musculus adductor magnus and in the red musculus pyramidalis of the rat: glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate, fructose-1-6-diphosphate, -glycerophosphate, lactate, pyruvate, and dihydroxyacetone phosphate.The conditions compared are: Inactin (5-ethyl-5(methyl-propyl)-2-thiobarbituric acid)-anesthesia, diethyl ether anesthesia, and tetanic contraction under Inactin anesthesia.The histological assay with Sudan-black B staining shows 34.2±7.3% dark fibers in m. pyramidalis and 0.2±4.8% dark fibers in m. adductor magnus.Glucose-1-phosphate, fructose-1-6-diphosphate, and -glycerophosphate are elevated under ether anesthesia in both muscles versus Inactin anesthesia by 100–200%.Lactate in both muscles and pyruvate in the red muscle are slightly elevated under ether (by 40%) versus Inactin anesthesia.Under tetanic contraction the metabolites studied rise considerably in both muscles.As glycogen is lowered in rat muscle under ether [9], the present results suggest an activation of glycogen phosphorylase and of phosphofructokinase in both the red and the white muscle under ether anesthesia, which results in augmented glycolysis.The comparatively small increment of pyruvate and lactate in the presence of a high increment of -glycerophosphate under ether anesthesia is considered to indicate an asynchronous activation of fibers with unimpaired circulation and oxidative metabolism.     

Synaptic responses to mechanical stimulation in calyceal and bouton type vestibular afferents studied in an isolated preparation of semicircular canal ampullae of chicken

Summary Relationships between the response patterns of semicircular canal afferents to mechanical stimulation and the morphologies of their peripheral endings were investigated in an isolated preparation of the anterior semicircular canal ampulla of chicken, using a combination of electrical recording with intracellular injections of Lucifer Yellow CH. The hair bundle mechanical stimulus was applied in a diffuse manner by a glass rod vibrating in the nearby bathing medium. Two types of spike discharge patterns and postsynaptic potentials were recorded. One type was found exclusively in the bouton type afferent and demonstrated a phasic increase of firing frequency and transient depolarizing postsynaptic potentials at the beginning of mechanical stimulation. These synaptic potentials were also observed spontaneously and their amplitudes were increased by membrane hyperpolarization. The other type was found exclusively in afferents with calyceal endings and showed a tonic increase of spiking frequency and depolarizing DC postsynaptic potentials with superimposing AC responses at the frequency of the mechanical stimulation. Amplitudes of postsynaptic potentials were increased by hyperpolarization. Hair cells generated depolarizing DC transduction potentials superimposed with AC potentials at frequency of the mechanical stimulation. The spontaneous spike discharging patterns of afferent nerve fibres were classified either as a regular type (CV < 0.10) or as an irregular type (CV > 0.25) on the basis of coefficient of variation (CV) of interspike intervals. The spontaneous firing rate of regular units was higher than that of irregular units. Several membrane characteristics are different between these two types of afferent fibers; irregular units had short membrane time constants and fast spikes associated with clear spike-afterhyperpolarization. These features fit with the fact that irregular units tend to have phasic responses to mechanical stimulation while regular units typically have tonic responses. Irregular units had bouton endings with an average axonal diameter thicker than the regular units which had calix endings.     

The effects of oxytocin on the pattern of electrical propagation in the isolated pregnant uterus of the rat

 In the isolated pregnant myometrium of the rat, the pattern of propagation was investigated by recording simultaneously from 240 different extracellular sites while the contraction of the tissue was recorded isometrically. Analysis of all recorded electrograms allowed the two-dimensional spread of activity in the myometrium to be reconstructed. From these activation maps, the conduction velocities were measured in the longitudinal, oblique and transversal directions. At low concentrations (10^–9 and 5×10^–9 M), oxytocin significantly increased the frequency and duration of electrical bursts and the average spike intervals, without affecting the homogeneity of action potential propagation, concomitant with a significant increase in the amplitude of contractions. At high concentrations (10^–8 and 5×10^–8 M), oxytocin induced conduction blocks and the size of inexcitable areas was increased, concomitantly with an increase in muscle contractures. In contrast, the conduction velocities in the longitudinal, oblique and circular directions were not influenced by oxytocin at any concentrations. Received: 9 June 1998 / Received after revision: 14 September 1998 / Accepted: 23 September 1998     

Effect of beta adrenergic stimulation and blockade on cutaneous reactivity to histamine.

It has been previously demonstrated that iontophoresis of beta adrenergic agents will alter the size of immediate hypersensitivity skin tests. It was unclear whether this alteration was due to an effect on the dermal mast cell (inhibition of histamine release) or on the cutaneous vasculature (inhibition of capillary permeability). For this reason isoproterenol, propranolol, diphenhydramine as a positive control, and saline as a negative control were iontophoresed onto the forearm of 10 atopic and 10 nonatopic adult subjects. In order to bypass histamine release from mast cells the patients were then challenged directly with histamine by the "prick" technique. The size of the resultant wheals was noted. The data obtained allowed the following conclusions: (1) The atopic group responded to histamine with greater wheal size than the nonatopic group. (2) Iontophoresis of diphyenhydramine effectively reduced the magnitude of the histamine wheal in both groups. (3) Isoproterenol decreased the wheal size in both groups. (4) Propranolol increased the wheal size in only the nonatopic group. (5) The successful modulation of the histamine-induced wheal and flare indicated that these drugs, regardless of their effect on the dermal mast cell, exert a measurable effect on the target organ (vasculature).     

The differential effect of cooling on the responses of splenic capsular and vascular smooth muscle to nerve stimulation and noradrenaline

The responses of the capsular and vascular smooth muscle of the dog's spleen to splenic nerve stimulation and to infused noradrenaline have been studied in the isolated, blood-perfused preparation at 37°C, at 27°C and again after rewarming to 37°C. It was found that cooling per se had no effect on perfusion pressure but reduced splenic arterial blood flow, and caused no appreciable alteration in spleen volume. The increase in splenic flow resistance in response to nerve stimulation and noradrenaline was significantly greater at 27°C than at 37°C, but the concomitant reduction in spleen volume was significantly reduced.The enhanced effect of splenic nerve stimulation and noradrenaline on splenic flow resistance is discussed in terms of the relative contributions of an increased smooth muscle response and increased blood viscosity. The different effects of cooling on the responses of splenic vascular and capsular smooth muscle to nerve stimulation and noradrenaline are discussed in the context of the effect of cooling on other vascular and non-vascular smooth muscle.This work was supported by a grant from the Medical Research Council     

Effect of electrical cutaneous stimulation on the level of succinate dehydrogenase activation and changes in glutamatergic synaptic transmission in response to sensory stimulation

It is shown that the rise of succinate dehydrogenase activity in the hippocampus depends on the number of sensory stimuli presented before decapitation, which correlates with changes in the efficiency of glutamatergic synaptic transmission in hippocampal sections from the same animal. Electrocutaneous stimulation potentiates the activation of succinate dehydrogenase induced by sensory stimulation probably due to enhanced glutamate release. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 123, No. 4, pp. 404–407, April, 1997     

The effect of experimental frost-bite on the responses of the rabbit ear-artery to adrenergic and electrical stimulation

The aim of the present investigation was to study the effect of sub-zero temperatures on the adrenergic activated, smooth muscle-contraction of a peripheral blood-vessel. The central ear-artery of the rabbit was used for this purpose. The artery was stimulated to contract in vitro by activation of phentolamine sensitive, post-junctional, a-adrenoceptors by use of noradrenaline, or by noradrenaline released from noradrenergic nerves in the blood-vessel following electrical field stimulation. The effect of freezing the tissue in vivo for 15 min at sub-zero temperatures (–4, - 6 and – 9 ^oC) was studied in vitro. Exposure to – 4 and – 6 ^oC did not alter the apparent affinity (ED₆₀) of noradrenaline significantly, when measured immediately, or 2 or 6 days after exposure. The maximal response to noradrenaline was reduced by approximately 54, 74 and 100% following exposure to – 4 , – 6 and – 9 ^oC, respectively. The response was completely restored after 2 and 6 days of regeneration in vivo following exposure to – 6 ^oC, whereas the response after exposure to – 9 ^oC was restored by only about 8 and 30% after 2 and 6 days regeneration, respectively. The maximal response to electrical field stimulation, which was completely inhibited by tetrodotoxin and phentolamine, was reduced by approximately 92% after exposure for 15 min to –4 and – 6 ^oC, while it was completely inhibited after exposure to – 9 ^oC. The response was restored by only 15–20% following 2 and 6 days in vivo after exposure to – 6 ^oC. No regeneration of the contraction induced by the electrical stimulation was observed after 2 or 6 days following exposure to –9 ^oC. The results of the present study suggest that noradrenergic nerves in the central ear-artery of the rabbit are more sensitive to subzero temperatures than are the post-junctional, noradrenergic α-receptors and the smooth muscle of the blood-vessel. The damage induced by freezing appeared to be both time and temperature dependent and there was only limited restoration of the nervous function 6 days after severe freezing.     

The responses of pericruciate cortical neurones to distal forepaw electrical stimulation in the unanaesthetized,unrestrained cat

Summary Experiments were performed to examine the responses of cortical neurons in the pericruciate cortex to cutaneous afferent input from the distal forepaw. Ninty-nine cortical neurons responding to electrical stimulation of the forepaw were recorded from four cats. Their response latencies ranged from 6 to 23 ms. The units had cutaneous receptive fields which ranged in size from those restricted to one digit to those extending over the whole forelimb. They were recorded from area 4 and area 3. Intracortical microstimulation at the recording sites activated either the distal or proximal musculature of the forelimb. When the characteristics obtained from each recording site were examined as a group of features, a uniform population emerged which was significantly different from the rest of the sample. These units had 1) the shortest latency responses to distal forepaw electrical stimulation, 2) the shortest duration of evoked discharge, 3) the smallest distal cutaneous receptive fields. Such units were recorded at the border between areas 3 and 4, at sites which on microstimulation resulted in movements of the distal forepaw musculature.     

The contribution of adrenergic mechanisms to frequency potentiation and to paired stimulation in guinea pig isolated atrial tissue

Summary In order to establish whether adrenergic mechanisms are involved in frequency induced potentiation and in the positive inotropic response to paired stimulation, the effect of adrenergic drugs on both processes were studied in guineapig isolated left auricles. 1. Owing to the positive inotropic effect of noradrenaline and isoproterenol the relative increase in contractile force at rising frequencies proved less pronounced than in control experiments, although the absolute maximal force that developed was higher in presence of the sympathomimetic drugs. 2. Pretreatment of the guinea-pigs with high doses of reserpine did not impair both potentiation phenomena in the isolated organs. Surprisingly, frequency potentiation proved even slightly increased in the noradrenaline-depleted organs. 3. A low concentration of propranolol (10^–9 M) did not affect both potentiation phenomena. Propranolol, in such concentration (10^–6 M) that unspecific, quinidine-like effects occurred diminished both frequency potentiation and the response to paired stimulation. 4. The results suggest that adrenergic mechanisms do not play any significant role in both potentiation phenomena.