Accumulation of cardiolipin and lysocardiolipin in fibroblasts from Tangier disease subjects

Tangier disease (TD) is an inherited disorder of lipid metabolism characterized by very low high density lipoprotein (HDL) plasma levels, cellular cholesteryl ester accumulation and reduced cholesterol excretion in response to HDL apolipoproteins. Molecular defects in the ATP binding cassette transporter 1 (ABCA1) have recently been identified as the cause of TD. ABCA1 plays a key role in the translocation of cholesterol across the plasma membrane, and defective ABCA1 causes cholesterol storage in TD cells. Not only cholesterol efflux, but also phospholipid efflux was shown to be impaired in TD cells. By use of thin layer chromatography, high performance liquid chromatography and time-of-flight secondary ion mass spectrometry, we characterized the cellular phospholipid content in fibroblasts from three homozygous TD patients. The cellular content of the major phospholipids was not found to be significantly altered in TD fibroblasts. However, the two phospholipids cardiolipin and lysocardiolipin, which make up minute amounts in normal cells, were at least 3-5-fold enriched in fibroblasts from TD subjects. A structurally closely related phospholipid (lysobisphosphatidic acid) has recently been shown to be enriched in Niemann-Pick type C, another lipid storage disorder. Altogether these data may indicate that the role of these phospholipids is a regulatory one rather than that of a bulk mediator of cholesterol solubilization in sterol trafficking and efflux.

Non-herbal nutritional supplements-the next wave: a comprehensive review of risks and benefits for the C-L psychiatrist

The continuing popularity of complementary medicine has led to the frequent appearance of new products in the marketplace. Non-herbal supplements are now a popular choice for patients seeking relief from a variety of medical conditions. As with herbal medicines, there are concerns about the safety of these products in those with physical illness. Clearly, consultation-liaison psychiatrists will encounter patients using non-herbal products or inquiring about them. This article seeks to provide knowledge about the risks and benefits of non-herbal supplements that consultation-liaison psychiatrists are likely to encounter.

Modulation of presynaptic inhibition and disynaptic reciprocal Ia inhibition during voluntary movement in spasticity

The aim of the study was to investigate whether impaired control of transmission in spinal inhibitory pathways contributes to the functional disability of patients with spasticity. To this end, transmission in the pathways mediating disynaptic reciprocal Ia inhibition and presynaptic inhibition was investigated in 23 healthy subjects and 20 patients with spastic multiple sclerosis during ankle dorsiflexion and plantar flexion. In healthy subjects, but not in spastic patients, the soleus H reflex was depressed at the onset of dorsiflexion (300 ms rise time, 20% of maximal voluntary effort). At the onset of plantar flexion, the soleus H reflex was more facilitated in the healthy subjects than in the patients. The H reflex increased more with increasing level of tonic plantar flexion and decreased more with dorsiflexion in the healthy subjects than in the spastic patients. Transmission in the disynaptic Ia reciprocal inhibitory pathway from ankle dorsiflexors to plantar flexors was investigated by conditioning the soleus H reflex by previous stimulation of the common peroneal nerve (conditioning-test interval 2-3 ms; stimulation intensity 1.05 times the motor response threshold). At the onset of dorsiflexion, stimulation of the common peroneal nerve evoked a significantly larger inhibition than at rest in the healthy subjects but not in the spastic patients. At the onset of plantar flexion the inhibition decreased in the healthy subjects, but because only weak inhibition was observed at rest in the patients it was not possible to determine whether a similar decrease occurred in this group. There were no differences in the modulation of inhibition during tonic plantar flexion and dorsiflexion in the two populations. Presynaptic inhibition of Ia afferents terminating on soleus motor neurones was evaluated from the monosynaptic Ia facilitation of the soleus H reflex evoked by femoral nerve stimulation. Femoral nerve facilitation was decreased at the onset of dorsiflexion and increased at the onset of plantar flexion in the healthy subjects and patients, but the changes were significantly greater in the healthy subjects. There was no difference between the two populations in the modulation of presynaptic inhibition during tonic plantar flexion and dorsiflexion. It is suggested that the abnormal regulation of disynaptic reciprocal inhibition and presynaptic inhibition in patients with spasticity is responsible for the abnormal modulation of stretch reflexes in relation to voluntary movement in these patients. Lack of an increase in reciprocal inhibition and presynaptic inhibition at the onset of dorsiflexion may be responsible for the tendency to elicitation of unwanted stretch reflex activity and co-contraction of antagonistic muscles in patients with spasticity.

The effect of baclofen on the transmission in spinal pathways in spastic multiple sclerosis patients

OBJECTIVES

To measure the effect of baclofen on the transmission in different spinal pathways to soleus motoneurones in spastic multiple sclerosis patients.

METHODS

Baclofen was administered orally in 14 and intrathecally in 8 patients. H(max)/M(max), presynaptic inhibition by biceps femoris tendon tap of femoral nerve stimulation, depression of the soleus H-reflex following previous activation of the Ia afferents from the soleus muscle (i.e. postactivation depression), disynaptic reciprocal Ia inhibition of the soleus H-reflex and the number of backpropagating action potentials in primary afferents, which may be a sign of presynaptic inhibition, were examined.

RESULTS

Baclofen depressed the soleus H(max)/M(max) ratio significantly following oral and intrathecal baclofen. None of the two tests of presynaptic inhibition, or the postactivation depression or the disynaptic reciprocal Ia inhibition of the soleus H-reflex were affected by baclofen administration. Also the action potentials of the primary afferents were unchanged during baclofen administration.

CONCLUSIONS

The antispastic effect of baclofen is not caused by an effect on the transmitter release from Ia afferents or on disynaptic reciprocal Ia inhibition. One possible explanation of the depression of the H-reflex by baclofen is suggested to be a direct depression of motoneuronal excitability.

High expression of MHC I in the tibialis anterior muscle of a paraplegic patient

A long-term paraplegic man presented exclusively (>99%) myosin heavy chain I (MHC I) in the tibialis anterior muscle (TA). This was coupled to a slow speed of contraction, a high resistance to fatigue, and a rapid resynthesis of phosphocreatine after an electrically evoked fatiguing contraction when compared with the TA muscles of 9 other paraplegic individuals. In contrast, the MHC composition of his vastus lateralis, gastrocnemius, and soleus muscles was that expected of a muscle from a spinal cord injured individual. This information may be of clinical importance in terms of the expected morphological and functional adaptations of skeletal muscle to different types of electrical stimulation therapy.

Amplitude of the maximum motor response (Mmax) in human muscles typically decreases during the course of an experiment

It was shown that the amplitude of the soleus Mmax and Hmax responses decreases in the course of long-lasting H-reflex studies. The peak-to-peak amplitudes of the Mmax and Hmax responses in the soleus muscle (and the Mmax in the tibialis anterior muscle and small hand muscles) were measured repeatedly for 1-3 h in 20 subjects. 3-5 Mmax responses and 5-10 Hmax responses were elicited about every 3 min while the subject was at rest. Decreases in the soleus Mmax response of up to 50.5% (mean 20.5% SEM 2.2) and of the soleus Hmax of up to 49.7% (mean 19.1% SEM 3.7) in relation to the amplitudes measured at the beginning of the experiment were seen in 17 subjects. In 3 subjects no Mmax amplitude decrease was seen. The maximum decrease was reached between 10 and 100 min (mean 44.2 min SEM 4.3). An Mmax amplitude decrease was also seen in the tibialis anterior muscle and in two small hand muscles. In some subjects the decrease of the Mmax response seemed to be initiated by the infrequent supramaximal stimulations. The possible causes for this amplitude reduction, as well as the methodological consequences of these findings for H-reflex studies and fatigue studies, are briefly discussed.

[Diagnosis of polyneuropathies]

The accurate diagnosis of peripheral neuropathy is important with respect to the therapeutic possibilities and limitations, which are especially relevant in immune-mediated polyneuropathies. These polyneuropathies may be axonal or demyelinating and have an acute or chronic course, and they may be difficult to distinguish from non-treatable neuropathies on clinical grounds. Efforts have been made to establish clinical, neurophysiological, morphological, biochemical, immunological and molecular biological criteria to attain specific diagnosis. This has shown heterogeneity not only within the treatable neuropathies, which may have implications for the treatment. It has also been shown that hereditary or diabetic polyneuropathy may have features which respond to immunosuppressive treatment. Molecular biology studies have revealed markers for the diagnosis of hereditary neuropathy, and have in some instances also delineated the gene product.

Changes in transmission across synapses of Ia afferents in spastic patients

The transmission across synapses of Ia afferents on spinal motor neurons was investigated in 30 healthy subjects and 25 spastic multiple sclerosis patients. Slow passive stretch (17 degrees/s of the soleus muscle evoked a pronounced depression of the soleus Hoffmann reflex (H-reflex) lasting for more than 10 s in the healthy subjects. This depression was less pronounced and had a shorter duration in the spastic patients. A tap applied to the biceps femoris tendon also produced an inhibition of the soleus H-reflex, which was larger in the healthy subjects than in the spastic patients. This inhibition only lasted for 300-400 ms. Finally, stimulation of the femoral nerve (FN) produced a facilitation of the soleus H-reflex, which was larger in the spastic patients than in the healthy subjects. The inhibition of the H-reflex evoked by the biceps femoris tendon tap is known to be caused by presynaptic inhibition of the Ia afferents, which mediate the reflex. The facilitation of the soleus H-reflex produced by FN stimulation has also been shown to be influenced by changes in presynaptic inhibition. The increased facilitation from the FN and the decreased inhibition from the biceps femoris tendon tap onto the soleus H-reflex in spastic patients are thus both compatible with a deficient presynaptic inhibition in these subjects. The long lasting depression of the reflex evoked by a previous slow stretch of the soleus muscle is most likely caused by a decrease of the probability of transmitter release from the Ia afferents. The decrease of this depression in spastic patients suggests that mechanisms other than presynaptic inhibition may contribute to changes in the efficiency of transmission across the synapses of Ia afferents in spastic patients and thus contribute to the exaggeration of stretch reflexes seen in these patients.

Central control of reciprocal inhibition during fictive dorsiflexion in man

The size of the soleus Hoffmann reflex (H-reflex) was measured in six healthy human subjects before and after transmission in the common peroneal nerve (CPN) was blocked reversibly by local injection of lidocaine. It was found that the H-reflex at rest increased after the block. When the subjects attempted to perform a dorsiflexion while the CPN was blocked ("fictive dorsi flexion"), the soleus H-reflex was strongly depressed. Stimulation of the CPN proximal to the block elicited a short-latency inhibition of the soleus H-reflex, which was probably mediated by reciprocal Ia interneurones. This inhibition never increased during dorsiflexion relative to rest prior to the CPN block, but after the block a significant increase in inhibition was seen during fictive dorsiflexion in three subjects. Stimulation of the femoral nerve (FN) elicited a short-latency monosynaptic Ia facilitation of the soleus H-reflex. This facilitation was found to decrease during dorsiflexion relative to rest before the block as well as during fictive dorsiflexion after the block. The decrease in the H-reflex during fictive dorsiflexion demonstrates that although an increased Ia-afferent feedback via the gamma-loop may contribute to reciprocal inhibition when transmission in the CPN is intact, a noticeable, centrally mediated inhibition may occur in the absence of this feedback. It is suggested that this inhibition is caused by central facilitation of interneurones mediating disynaptic Ia inhibition as well as interneurones mediating presynaptic inhibition of Ia afferents.

Central control of disynaptic reciprocal inhibition in humans

The disynaptic pathway from muscle spindle Ia afferents to motoneurones of the antagonist muscle is one of the best studied pathways in the spinal cord. Early animal studies--mainly in the cat--have provided a detailed knowledge of the pathway itself and of the integration of segmental and supraspinal convergence at the interneuronal level. Although this knowledge was used to formulate hypotheses on the function of the pathway during natural movements, the reduced animal preparation limited the possibilities of testing these ideas. However, such information has more recently been obtained from human subjects by using indirect electrophysiological techniques. In most of these experiments the disynaptic Ia inhibition was demonstrated as a short-latency depression of a monosynaptic test reflex (H-reflex) following a conditioning stimulation of the antagonist nerve. Changes in the size of this depression during voluntary tasks were then taken as evidence of a central regulation of the pathway. It has for example been demonstrated in this way that the brain regulates the Ia inhibitory interneurones in parallel with their corresponding motoneurones during extension-flexion movements, but not during co-contraction of antagonistic muscles. The importance of the central control of the pathway has also been emphasized by the finding of a disordered regulation of its activity in patients with lesions of the brain. This may possibly contribute to the inappropriate co-contraction of antagonistic muscles observed in some of these patients. It seems reasonable to expect that this kind of experiment in the future may contribute significantly to the knowledge of the central control of spinal motor mechanisms.

Disynaptic reciprocal inhibition of ankle extensors in spastic patients

The soleus Hoffmann-reflex (H-reflex) was conditioned by a preceding stimulation of the common peroneal nerve in 74 healthy control subjects and 39 patients with spasticity in the lower extremities due to multiple sclerosis. At a conditioning-test interval of 1-3 ms a decrease of the size of the soleus H-reflex was seen in the healthy subjects. The decrease was most likely caused by disynaptic reciprocal Ia inhibition (Crone et al., 1987). In the spastic patients a similar short-latency inhibition was rarely seen. On the contrary, in several patients a facilitation was seen at a conditioning-test interval of 3-4 ms. A short-latency inhibition as pronounced as in healthy subjects was seen in four patients. These four patients did not differ from the other patients regarding the degree of spasticity or any other clinical parameter. However, they all used an external peroneal nerve stimulator daily as a walking aid. It is suggested that the lack of short-latency reciprocal inhibition reflects a deficient control of the interneurons which mediate this inhibitory spinal mechanism between antagonistic muscles in man. This might contribute to the pathophysiology of spasticity and it might be related to the frequent occurrence of co-contraction of functionally antagonistic muscles during gait in spastic patients. The existence of a pronounced reciprocal inhibition in patients receiving frequent stimulation of the peroneal nerve may suggest that regular activation of peripheral nerves is of importance for the maintenance of the activity in spinal pathways.

Reciprocal inhibition in man

Reciprocal inhibition is the automatic antagonist alpha motor neurone inhibition which is evoked by contraction of the agonist muscle. This so-called natural reciprocal inhibition is a ubiquitous and pronounced phenomenon in man and must be suspected of playing a major role in the control of voluntary movements. The spinal pathways underlying this inhibitory phenomenon were studied. The disynaptic reciprocal Ia inhibitory pathway between the tibial anterior muscle and the soleus alpha motor neurones was identified and described in man. It was shown that the inhibition can be evoked in most healthy subjects at rest, but the degree of inhibition varies considerably from one subject to another. It was concluded that it corresponds to the disynaptic reciprocal Ia inhibitory pathway which has been extensively described in animal experiments. The disynaptic reciprocal inhibition was shown to increase during the dynamic phase of a dorsiflexion movement of the foot, but not during the tonic phase. However, when the peripheral afferent feedback from the contracting muscle was blocked by ischaemia, an increase of the inhibition was revealed also during the tonic phase of the dorsiflexion. The concealment of this increase during unrestrained peripheral feedback from the muscle was thought to be due to the post-activation depression mechanism; a mechanism which was described further and which probably involves reduced transmitter release at Ia afferent terminals as a result of previous activation of these afferent fibers. Hence the hypothesis was supported that alpha motor neurones and the corresponding inhibitory interneurones, which project reciprocal inhibition to the antagonist motor neurones, are activated in parallel during voluntary contraction of agonist muscles. An additional reciprocal inhibitory mechanism, the long latency reciprocal inhibition, was described between the tibial anterior muscle and the soleus alpha motor neurones. It was shown to be evoked by group I afferent activity and it was seen at a conditioning-test interval of 3-6 msec. It was initiated by supraspinal pathways and it was seen only during dorsiflexion of the foot. The pathway underlying this inhibitory mechanism is unknown, but it was suggested that it was mediated by a propriospinal pathway. The possible contribution to reciprocal inhibition of presynaptic inhibition of soleus Ia afferent fibers was studied by an indirect method. It was concluded that this presynaptic inhibition was increased during even slight dorsiflexion of the foot and that the increase was mainly dependent upon the peripheral afferent input from the contracting muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

H-reflexes are smaller in dancers from The Royal Danish Ballet than in well-trained athletes

The size of the maximal H-reflex (Hmax) was measured at rest and expressed as a percentage of the maximal M-response (Mmax) in 17 untrained subjects, 27 moderately trained subjects, 19 well-trained subjects and 7 dancers from the Royal Danish Ballet. The Hmax/Mmax was significantly larger in the moderately and well-trained subjects than in the untrained subjects but smaller in the ballet dancers. It is therefore suggested that both the amount and the type of habitual activity may influence the excitability of spinal reflexes.

Central facilitation of Ia inhibition during tonic ankle dorsiflexion revealed after blockade of peripheral feedback

Recent studies have reported that no increase of the disynaptic reciprocal inhibition can be observed during tonic voluntary dorsiflexion of the foot as compared to rest, when the size of the control H-reflex is kept constant. Other studies have, however, shown that a voluntary contraction evokes a strong and long-lasting depression of the synaptic transmission from Ia afferents to motoneurones, most likely secondary to activation of these afferents during the contraction (post-activation depression). It was thought that this effect could also interfere with the demonstration of a central facilitation of the reciprocal inhibition during movement. The amount of disynaptic Ia reciprocal inhibition from the pretibial flexors to the soleus H-reflex was therefore estimated in normal human subjects at rest and during voluntary tonic dorsiflexion before, during and after blocking the peripheral feedback from the investigated muscles. It was observed that the reciprocal inhibition measured during dorsiflexion increased during occlusion of the blood supply to the leg, reaching a maximum of inhibition after 30 min of ischaemia. After release of the ischaemia the inhibition gradually decreased to its pre-ischaemic level. It is therefore suggested that the brain facilitates transmission in the Ia disynaptic reciprocal pathway during tonic voluntary dorsiflexion of the foot, but that this facilitation is normally not observed due to a post-activation depression following the peripheral feedback activation during the movement.

Sensitivity of monosynaptic test reflexes to facilitation and inhibition as a function of the test reflex size: a study in man and the cat

In parallel experiments on humans and in the cat it was investigated how the sensitivity of monosynaptic test reflexes to facilitation and inhibition varies as a function of the size of the control test reflex itself. In man the monosynaptic reflex (the Hoffmann reflex) was evoked in either the soleus muscle (by stimulation of the tibial nerve) or the quadriceps muscle (by stimulation of the femoral nerve). In the decerebrate cat monosynaptic reflexes were recorded from the nerves to soleus and medial gastrocnemius muscles; they were evoked by stimulation of the proximal ends of the sectioned L7 and S1 dorsal roots. Various excitatory and inhibitory spinal reflex pathways were used for conditioning the test reflexes (e.g. monosynaptic Ia excitation, disynaptic reciprocal inhibition, cutaneous inhibition, recurrent inhibition, presynaptic inhibition of the Ia fibres mediating the test reflex). It was shown that the additional number of motoneurones recruited in a monosynaptic test reflex by a constant excitatory conditioning stimulus was very much dependent on the size of the test reflex itself. This dependency had the same characteristic pattern whatever the conditioning stimulus. With increasing size of the test reflex the number of additionally recruited motoneurones first increased, then reached a peak (or plateau) and finally decreased. A similar relation was also seen with inhibitory conditioning stimuli. The basic physiological factors responsible for these findings are discussed. Finally, the implications for the interpretation of experiments in man with the H-reflex technique are considered.

News From the Alveoli

Recent studies show that the alveolar epithelium performs solute-coupled fluid transport in the direction from the alveolar spaces to lung interstitial fluid. Na+-K+-ATPase plays a prime role for assuring the "dry" character of the alveoli.

Methodological implications of the post activation depression of the soleus H-reflex in man

A long lasting inhibition (greater than 8 s) of the soleus Hoffmann reflex (H-reflex) was evoked by a preceding soleus H-reflex, by a brief voluntary ankle flexor or extensor muscle contraction or by a tap applied to the Achilles tendon. The time course of this long lasting inhibition was similar in all these cases, suggesting that the same spinal mechanism is involved. Furthermore, it was shown that the post-activation depression may interfere with the determination of inhibitory or facilitatory effects on the H-reflex. It is stressed that when the onset of inhibitory or facilitatory effects on the soleus H-reflex is to be determined in relation to start of an ankle movement, either very long stimulus intervals (greater than 8 s) must be used, or the onset must be determined in relation to a reference value of the soleus H-reflex, which may be influenced by the long lasting inhibitory effect, but not yet by the succeeding muscle contraction.

Spinal mechanisms in man contributing to reciprocal inhibition during voluntary dorsiflexion of the foot

1. The inhibition of the soleus Hoffmann reflex (H reflex) during voluntary dorsiflexion of the foot--henceforth referred to as 'natural' reciprocal inhibition--was found to be initiated 50 ms before the onset of the EMG activity in the tibialis anterior muscle and to increase gradually during a ramp-and-hold dorsiflexion. There was a positive correlation between strength of tonic dorsiflexion and amount of 'natural' reciprocal inhibition. 2. The change of activity in the disynaptic and a long-latency group Ia inhibitory pathway and the change in presynaptic inhibition of the Ia fibres mediating the soleus H reflex were tested separately during ramp-and-hold dorsiflexion as well as during tonic dorsiflexion of the foot, and the results were compared with the development of the 'natural' reciprocal inhibition of the unconditioned soleus H reflex. 3. The disynaptic group I inhibition of soleus motoneurones was increased, as compared to rest, during the dynamic phase of a ramp-and-hold dorsiflexion movement, but the inhibition generally did not increase during tonic dorsiflexion of the foot. 4. The long-latency group I inhibition was seen only during dorsiflexion of the foot. It appeared around 50 ms before tibial anterior EMG activity and there was a positive correlation between strength of tonic dorsiflexion and amount of this long-latency inhibition. 5. Presynaptic inhibition of Ia afferents terminating on soleus motoneurones was estimated by an indirect method. The increase of presynaptic inhibition started soon after the onset of the ramp-and-hold dorsiflexion, and gradually became more pronounced during the ramp phase. The amount of presynaptic inhibition was positively correlated with strength of tonic dorsiflexion. 6. It is concluded that all investigated mechanisms may contribute to the 'natural' reciprocal inhibition and it seems that the different pathways are used differentially during different types of movement.

Growth of colorectal carcinoma cells: regulation in vitro by gastrin, pentagastrin and the gastrin-receptor antagonist proglumide

The growth-regulating effects of pentagastrin, gastrin and the gastrin-receptor antagonist proglumide were investigated in three established cell lines derived from human colorectal carcinomas in vitro and after transplantation into nude mice. In vitro a significant increase of cell growth in the SW 403 cell line incubated with pentagastrin or gastrin was observed. In the Lovo cell line this effect was only detected after synchronization of cell growth. Pentagastrin and gastrin had no effect on the growth of the Ls 174 T cell line. Proglumide reduced cell proliferation in all three cell lines as well as in the L929S cell line derived from fibroblasts, which served as control. After transplantation into nude mice all tumor cell lines increased, Lovo and Ls 174 T as undifferentiated tumor, SW 403 as differentiated. Pentagastrin increased and proglumide decreased growth in SW 403 tumors, whereas no effect was observed on Ls 174 T and Lovo tumors. We therefore conclude that growth of some colorectal carcinomas is regulated by gastrin, but that the effect of proglumide is unspecific rather than related to blockage of gastrin receptors. The growth-regulating effect of gastrin could be due to tumor differentiation.

Cellular effects of beta-adrenergic and of cAMP stimulation on potassium transport in rat alveolar epithelium

Alveolar fluid absorption is greatly enhanced by cAMP and by beta-adrenergic agonists via an increase in Na+ transport. Little is known about K+ homeostasis under these circumstances. We studied K+ transport across alveolar epithelium in isolated perfused rat lungs stimulated either by dibutyryl-cAMP or isoproterenol. K+ fluxes and the apparent permeability of 86Rb across the epithelium (alveoli to plasma) were interpreted according to a model involving two types of cells, B and L, distinguished by the location of Na+-K+-ATPases (basal and luminal). Water is considered to be absorbed by B cells in a solute-coupled process energized by a basolateral Na+-K+-ATPase that is stimulated by isoproterenol and cAMP. K+ transport out of the alveoli is due to the activity of a Na+-K+-ATPase located in the apical membrane of L cells. In the present study net transport rate of K+ was -0.5 +/- 0.15 nmol/s, n = 20 (out of alveoli) in control conditions. When the epithelium was stimulated by dibutyryl-cAMP (10(-4) mol/l) net absorption of K+ reversed to net 'secretion' into alveoli (3.2 +/- 0.31 nmol/s), fluid absorption was not stimulated. K+ 'secretion' was abolished by apical Ba2+, indicating it was due to opening of apical K+ channels. Basolateral ouabain reversed net K+ 'secretion' to net absorption indicating that K+ entry into alveoli was dependent on activity of B cell basolateral Na+-K+-ATPase (masking simultaneous K+ removal by apical L cell Na+-K+-pump). When larger concentrations of dibutyryl-cAMP (10(-3) mol/l) or when isoproterenol were used to stimulate the epithelium there was a tripling of fluid absorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Maintained changes in motoneuronal excitability by short-lasting synaptic inputs in the decerebrate cat

1. During investigation of the tonic stretch reflex in the unanaesthetized decerebrate cat we observed that a short train of impulses in Ia afferents from the soleus muscle (or its synergists) may cause a prolonged activity in the soleus muscle as judged by EMG and tension recordings. This excitability increase, which outlasted the stimulus train, could stay virtually constant during long periods (even minutes), but could be terminated at any time by a train of impulses in, for example, the peroneal nerve. 2. Gradation of the strength of stimulation and the duration of the train of impulses show that the amount of maintained excitability increase depends-within some limits-on the total amount of Ia impulses. 3. In paralysed preparations a short train of impulses in Ia afferents from any part of the triceps surae, caused a maintained increase of the efferent activity in the nerves to triceps surae and a maintained increase of the triceps surae monosynaptic test reflex. These experiments demonstrate the existence of a central mechanism (in the spinal cord and/or the brain stem), which is responsible for the maintained excitability increase seen in motoneurones to the homonymous and synergic muscles. 4. In acute spinal preparations it was not possible to demonstrate any long-lasting excitability increase by a train of Ia impulses. Following intravenous administration of the serotonin precursor 5-hydroxytryptophan, mimicking the tonic activity of these pathways in the decerebrate state, it was again possible to elicit the long-lasting excitability increase by a train of impulses in Ia afferents. A subsequent I.V. injection of methysergide (a serotonin receptor blocker) abolished the long-lasting excitability increase. This set of experiments demonstrates that the basic mechanism responsible for the maintained excitability increase is located at segmental level, and involves serotonergic systems. 5. It was demonstrated that activation of several ipsilateral and crossed reflex pathways by trains of impulses in cutaneous or high-threshold muscle afferents could trigger a maintained excitability increase of those motoneurone pools which were activated by the stimulation. Trains of stimuli to facilitatory regions in the brain stem could also cause a long-lasting excitability increase of motoneurones. Furthermore, activation of all reflex pathways which mediate postsynaptic inhibition to a motor nucleus (including recurrent inhibition via Renshaw cells) could terminate the prolonged excitability increase of that particular motor nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Presynaptic inhibition of sympathetic fibers participating in vasodilatation in response to K+-induced contraction of frog skeletal muscle

Experiments were performed on an autoperfused transparent frog muscle (m. cutaneus pectoris) with the purpose of elucidating possible mechanisms of functional hyperaemia. The diameter of a primary arteriole was followed before and after a K+-induced contracture lasting 20 s. The vasodilatation following this period of activity was expressed as the diameter change relative to the maximal possible diameter increase. The results emphasize adenosine as an important substance participating in vasodilatation in active skeletal muscle, its effect possibly being presynaptic (prejunctional) inhibition of sympathetic vasoconstrictor fibers to arteriolar smooth muscle (sympathetic uncoupling), in addition to the well-known direct effect (relaxation) on vascular smooth muscle cells. The presence of a strong resting sympathetic tone was demonstrated by local application of phentolamine (7.1 X 10(-5) M) that led to a large diameter increase. The purinoceptor blocking agent, 8-phenyltheophylline (8-PTP) invariably attenuated post-contraction vasodilatation, the adenosine transport inhibitor dipyridamole (10(-5) M) increased the hyperaemia response. Lack of sympathetic arteriolar tone during hyperaemia was demonstrated by the absence of a dilatory effect of phentolamine applied in the post-contraction period. Conversely, blockage of purinoceptors by 8-PTP during and after the contracture allowed sympathetic discharge to continue as verified by application of phentolamine, now leading to further vasodilatation. We suggest that presynaptic inhibition of sympathetic nerve endings by adenosine participates in vasodilatation in frog skeletal muscle.

Apical sodium-sugar transport in pulmonary epithelium in situ

The presence of an apical sodium-coupled transport system for D-glucose in lung alveolar epithelial cells has been demonstrated in lungs instilled with Ringer's fluid and perfused with either blood or Ringer's fluid (Basset et al. (1987) J. Physiol. 384, 325-345). The direction of transport is from alveoli towards interstitium. The characteristics of the system were evaluated in similar preparations by use of sugar analogues such as alpha-methyl-glucopyranoside, 2-deoxyglucose, 3-O-methylglucose and L-glucose. The main finding was the presence of a transport system for alpha-methylglucopyranoside and 2-deoxyglucose in the apical cell membrane. This system was unaffected by phloretin. Both alpha-methylglucopyranoside and 2-deoxyglucose transports were inhibited by phloridzin and by the presence of glucose (10(-2) mol.l-1). Competition was demonstrated between D-glucose and alpha-methylglucopyranoside or 2-deoxyglucose, but not for 3-O-methylglucose or L-glucose. 3-O-Methylglucose was cleared as slowly as L-glucose. The results comply partly with those known from intestinal epithelium and kidney proximal tubular epithelium, but the handling of 3-O-methylglucose was different. The relative transport rates of Na+ and glucose are compatible with a Na+: glucose coupling ratio larger than one.

Potassium transport across rat alveolar epithelium: evidence for an apical Na+-K+ pump

1. Experiments were performed on rat lungs into which various solutions were instilled whilst the lungs were perfused with either whole blood or Ringer solution. Instillation of ion-free glucose solution led to a net flux of fluid and ions into the alveolar spaces. K+ ions entered faster than Na+ ions and reached a concentration about twice that in the perfusate. Ouabain in the perfusate (basolateral side) prevented the rise in alveolar K+ concentration above that in the perfusate, indicating a transcellular pathway. Ba2+ in the instillate (apical side) hindered the entry of K+ into alveoli, suggesting the presence of apical K+ channels. 2. When Ringer solution was instilled, K+ was continuously removed from the alveoli and the K+ concentration in the instillate remained constant or decreased slightly depending on the rate of fluid absorption. The net K+ efflux from alveoli to blood was 0.23 pmol/(cm2 s). When Ba2+ was added to the instillate the net K+ efflux increased to 0.36 pmol/(cm2 s). Apical ouabain reversed the K+ flux resulting in a net K+ flux of 0.19 pmol/(cm2 s) into the alveoli. This suggests the presence of an Na+-K+-ATPase located in the apical membrane of some alveolar cells. 3. The K+ transport from instillate (Ringer solution) to perfusate was traced by means of 86Rb which was added to the instillate. Ouabain in the instillate did not affect fluid absorption but reduced the apparent 86Rb permeability by 50% although the paracellular permeability (estimated with [3H]mannitol) was unaffected. This also indicates the presence of an apical Na+-K+-ATPase. When ouabain was added to the perfusate, the apparent 86Rb permeability doubled. These findings indicate that recirculation of 86Rb (and K+) occurs due to the activity of both apical and basolateral Na+-K+-ATPases. 4. When ouabain was placed on both sides of the epithelium, preventing transcellular transport, the passive 86Rb permeability was 10.3 x 10(-8) cm/s (assuming an alveolar surface area of 5000 cm2). This value agrees with the passive permeabilities for mannitol, Na+ and Cl- suggesting that the paracellular pathway acts as a water-filled neutral channel. 5. We conclude that K+ is 'secreted' into the alveoli and is also removed from the alveoli, both processes being energized by Na+-K+-ATPases placed on the basolateral and apical sides, respectively. It is likely that two functionally different cell types exist in the alveolar membrane. One type ('B cell') has a Na+-K+-ATPase located at the basolateral membrane and K+ channels situated luminally.(ABSTRACT TRUNCATED AT 400 WORDS)

cAMP and beta-adrenergic stimulation of rat alveolar epithelium. Effects on fluid absorption and paracellular permeability

The absorption of fluid (bicarbonate-buffered Ringer with 10 mmol/l glucose) instilled into rat lungs is a Na+-coupled process that takes place through two apical transport systems: an amiloride-sensitive Na+ transport and a Na+-glucose co-transport. Fluid absorption in isolated, perfused rat lungs and the permeability to 3H-mannitol of alveolar epithelium were studied in control conditions and during stimulation of the alveolar epithelium by cAMP or isoproterenol. cAMP led to a threefold increase in the rate of fluid absorption and to an increase in the paracellular permeability. A similar response was found following beta-adrenergic stimulation obtained with isoproterenol in the perfusate. The increase in fluid transport was due to enhancement of the amiloride-sensitive component of Na+ transport. The Na+-glucose co-transport which accounts for about 60% of fluid absorption in control conditions was depressed, possibly as a consequence of a depolarization of the apical alveolar cell membrane. Fluid absorption was reduced by 40% by apical amiloride (10(-4) mol/l) in control lungs and to an even larger extent in isoproterenol-stimulated lungs; it was completely abolished by amiloride in cAMP stimulated lungs. Since the Na+-glucose co-transport was still operative, this suggests that a secretory process was triggered. This was confirmed in experiments in which both kinds of transport were inhibited with a combination of amiloride and glucose-free Ringer. In these conditions fluid balance was zero in unstimulated lungs whilst fluid entry into alveoli was observed in isoproterenol and cAMP stimulated lungs.