bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcium dependency of the endothelium‐dependent hyperpolarization in smooth muscle cells of the rabbit carotid artery.
Authors: Chen G F , Suzuki H
Published: December 2014

1. In smooth muscle cells of the rabbit carotid artery, ACh (greater than 10(‐8) M) generated a hyperpolarization with two components (transient followed by sustained), only in the tissues with an intact endothelium. There were no detectable changes in the membrane potential, as elicited by ACh (up to 10(‐5) M) in tissues with no endothelium or in the presence of atropine (10(‐6) M). 2. Reduction of [Ca2+]o inhibited the sustained component which was not apparent in [Ca2+]o below 0.16 mM. In Ca2+‐free (EGTA‐containing) solution, the generation of the transient component of the hyperpolarization remained sustained but with a substantially reduced amplitude. 3. Procaine (greater than 10(‐6) M) inhibited the ACh‐induced hyperpolarization in a concentration‐dependent manner, and at a concentration of procaine (10(‐3) M) which caused substantial depolarization of the membrane, no detectable change was elicited by ACh. 4. Caffeine (10(‐6)‐10(‐3) M) produced a transient hyperpolarization, independent of the presence or absence of the endothelium, and inhibited the sustained component of the ACh‐induced hyperpolarization more so than the initial component. 5. A23187 (greater than 10(‐8) M) hyperpolarized the smooth muscle membrane in a concentration‐dependent manner, and this hyperpolarization was not generated in Ca2+‐free solution or in the absence of endothelial cells. 6. In intact tissues, pre‐treatment with A23187 resulted in a reduction of the subsequently generated ACh‐induced hyperpolarization, in an irreversible manner. 7. It would thus appear that in the rabbit carotid artery, the endothelium‐dependent hyperpolarization induced by ACh has Ca2+‐dependent and Ca2+‐independent components, and each may be related to the increase in endothelial [Ca2+]i by release from the intracellular store and by influx from the extracellular medium, respectively. The increased [Ca2+]i would trigger a release of an endothelium‐derived hyperpolarizing factor (EDHF) from the endothelial cells.
Motor‐unit force potentiation in adult cats during a standard fatigue test.
Authors: Gordon D A , Enoka R M , Stuart D G
Published: December 2014

1. The purpose of this study was to examine the time course of tetanic force during a standard fatigue test and to distinguish between the appearance of potentiation and fatigue among the four motor‐unit types of a cat hindlimb muscle. 2. Motor units of the tibialis posterior muscle in the adult cat were assigned to four categories (i.e. types S, FR, FI, FF) based on conventional criteria (Burke, Levine, Tsairis & Zajac, 1973). The mean (+/‐ S.D.) time course of peak force was constructed for each motor‐unit type and, within each type, for those units that potentiated (a greater than 3% increase in peak force compared to the initial value) and those that did not potentiate. 3. The average time courses of force differed between motor‐unit types. There was, however, considerable variability within each motor‐unit type. For the same relative force output, the forces exerted by slow‐twitch units were less variable than those exerted by fast‐twitch units. In addition, the variability among slow‐twitch units was relatively constant during the fatigue test while variability among fast‐twitch units either increased or decreased with time. 4. For a given motor‐unit type, the average time course of force did not depend on whether force in each tetanus was expressed as a peak value, an average peak value, or a force‐time integral. 5. Some motor units within each type exhibited potentiation. Most of the variability in the time course of the peak force for each motor‐unit type could be accounted for by the potentiating units. Motor units that exhibited only force decline (i.e. fatigue), regardless of unit type, had less variable time courses of peak force. Since potentiation was transient in some unit types, it was assumed that at least two opposing processes (i.e. fatigue and potentiation) occurred simultaneously in these units (see also, Krarup, 1981; Rankin, Enoka, Volz & Stuart, 1988; Garner, Hicks & McComas, 1989). 6. It is concluded that the expression of force potentiation throughout a fatiguing regimen is variable among motor units and that this is not related to conventional motor‐unit types. This dissociation suggests that the mechanisms that form the basis for the conventional distinction between motor‐unit types are different from those which lead to force potentiation.
Differential effects of hypoxia upon contractions evoked by potassium and noradrenaline in rabbit arteries in vitro.
Authors: Marriott J F , Marshall J M
Published: December 2014

1. A study has been made on isolated sections of rabbit femoral, renal and saphenous arteries of the effects of graded hypoxia (reducing bath PO2 from 110 mmHg, normoxia, to 55, 23 and 6 mmHg) upon contractile responses evoked by noradrenaline (NA) and KCl to 80% of maximum. 2. Potassium‐evoked contractions were not affected by moderate hypoxia but were reduced in all vessels to 70‐80% of the control response in normoxia, by exposure to either PO2 23 or 6 mmHg. Potassium‐evoked contractions were virtually abolished by Ca2(+)‐free Krebs solution and greatly reduced by verapamil (10 microM), indicating that they relied upon influx of extracellular Ca2+. 3. By contrast, NA‐evoked contractions were reduced in a graded fashion in all vessels by exposure to graded levels of hypoxia and at PO2 6 mmHg they were significantly more reduced than K(+)‐evoked contractions. Noradrenaline‐evoked contractions of femoral arteries were most affected, being reduced to 80% of control at PO2 55 mmHg, and to 28% and 6% of control at PO2 23 and 6 mmHg respectively. Contractions in renal arteries were least affected, being reduced to only 47% of control at PO2 6 mmHg. 4. Noradrenaline‐evoked contractions were reduced, but not abolished, in Ca2(+)‐free Krebs solution. In normoxia, they reached 42%, 35% and 25% of control responses in the presence of Ca2+ in femoral, renal and saphenous arteries respectively. The Ca2(+)‐free responses of the femoral and saphenous arteries were significantly different, indicating that the femoral arteries were least dependent and saphenous most dependent on influx of extracellular Ca2+ for contraction. 5. Contractions evoked by NA in Ca2(+)‐free Krebs solution were not significantly affected by PO2 55 mmHg. Those evoked in saphenous arteries were not affected by more severe hypoxia, but in renal arteries they were significantly reduced at PO2 23 mmHg, while in femoral arteries they were significantly reduced both at PO2 23 and at PO2 6 mmHg. 6. Verapamil produced changes similar to Ca2+ withdrawal. Contractions evoked by NA in the presence of verapamil were affected by hypoxia in a similar way to those evoked in the absence of Ca2+. 7. These results indicate that the inhibition of contraction induced by hypoxia is not simply dependent upon inhibition of Ca2+ influx. Instead, we propose that receptor‐operated rather than voltage‐operated processes are particularly vulnerable, there being inhibition of the components of contraction which are dependent on receptor‐operated Ca2+ influx and release of intracellular Ca2+.
Regulation of rat nerve blood flow: role of epineurial alpha‐receptors.
Authors: Kihara M , Low P A
Published: December 2014

1. Transperineurial arterioles connect the extrinsic (epineurial) and the intrinsic (endoneurial) microvasculatures. Our goal was to determine whether the extrinsic system regulated nerve blood flow locally and whether subperineurial and centrifascicular endoneurial nerve blood flows were regulated differentially. 2. The local application of noradrenaline resulted in a dose‐dependent reduction of nerve blood flow in subjacent endoneurium. Asymptotes of 78.8 and 76.3% vasoconstriction were recorded for subperineurial and centrifascicular endoneurial nerve blood flow, respectively, indicating near‐complete closure of capillaries. 3. Near‐identical concentrations required to generate 50% vasoconstriction (EC50) and asymptotes are suggestive of the fact that the two areas are not differentially regulated. 4. Local vasoconstriction cannot be due to a systemic effect of noradrenaline since a significant decrease in nerve blood flow occurs despite undetectable increases in plasma noradrenaline and mean blood pressure, or decrease in contralateral sciatic nerve blood flow. 5. There are small and statistically non‐significant reductions of the compound muscle action potential and conduction velocity in the sciatic‐tibial nerve following nerve ischaemia. 6. These findings suggest that epineurial arterioles control regional nerve blood flow and are primarily responsible for its regulation in subjacent endoneurial tissue.
The physiological basis of the minimally distinct border demonstrated in the ganglion cells of the macaque retina.
Authors: Kaiser P K , Lee B B , Martin P R , Valberg A
Published: December 2014

1. The minimally distinct border method involves setting the relative radiances of two adjacent, differently coloured fields until the border between them is minimally distinct. At these radiance settings, the two fields are found to be of equal luminance. The task shares with flicker photometry all the requirements of a photometric method. 2. We have recorded responses of macaque ganglion cells to such borders moved back and forth across the receptive field; the size of the luminance step across the border was systematically varied. 3. Phasic ganglion cells gave transient responses to such borders, consisting of an increase or decrease in firing rate depending on direction of luminance contrast and cell type (on‐ or off‐centre). Tonic ganglion cells gave sustained responses dependent on chromatic contrast across the border. 4. An analysis of phasic cell responses showed a minimum near equal luminance, suggesting their signal could readily support the minimally distinct border task. We could not devise a scheme whereby tonic cells could support the task. 5. Spectral sensitivity of phasic cells, determined from their minima, closely resembled the 10 deg luminous efficiency function, as required of a mechanism underlying the psychophysical performance. 6. For phasic cells, the minimum was independent of movement speed, and hence of eye movement velocity under natural viewing conditions. 7. Proportionality, additivity and transitivity are found psychophysically with the minimally distinct border method. All these properties were also exhibited by phasic cell responses. 8. Residual responses were present in individual phasic cells to equal‐luminance borders, probably due to a non‐linearity of M‐ and L‐cone summation. The amplitude of residual response depended on the wavelengths on either side of the border, and was zero for pairs of lights lying along a tritanopic confusion line. These residual responses could be correlated with residual border distinctness at equal luminance as reported psychophysically. 9. There was some variability in spectral sensitivity among phasic cells, and this could be described in terms of variability in weighting of the middle‐ and long‐wavelength cone inputs to each cell. With equal‐luminance borders, the residual response of the phasic cell population will thus be made up of the residual responses from individual cells and a contribution due to variation in spectral sensitivity among cells. 10. The responses of phasic ganglion cells thus form the physiological substrate of psychophysical performance on the minimally distinct border task. These cells also provide a residual signal to equal‐luminance borders which correlates with residual distinctness.(ABSTRACT TRUNCATED AT 400 WORDS)
A quantitative study of the central projection patterns of unmyelinated ventral root afferents in the cat.
Authors: Häbler H J , Jänig W , Koltzenburg M , McMahon S B
Published: December 2014

1. The ventral roots of the spinal cord contain a large number of unmyelinated primary afferent neurones. There is some controversy, however, about the function of these fibres and the route of their central projection. Here we have used electrophysiological techniques to quantify the central projection patterns of these neurones in the segment S2 of adult chloralose‐anaesthesized cats. 2. A total of 1185 single unmyelinated units were recorded in small filaments isolated from intact and de‐efferented ventral roots or intact dorsal roots of the segment S2 in nineteen cats. The projection patterns of these neurones were tested using supramaximal electrical stimulation of the pelvic and pudendal nerve (the main tributaries of the spinal nerve of this segment) and of the segmental companion root (dorsal or ventral as appropriate). 3. The principal finding of this study is that 85% of unmyelinated afferent axons in the ventral root are direct and exclusive projections. They constitute a separate class of afferents which is only capable of transmitting information from the periphery via the ventral roots. However, the proportion of these fibres that enter the central nervous system is unknown and it seems likely that some of them peter out as they approach the spinal cord and end blindly. The functional role of such afferents remains obscure. 4. For the remaining 15% of unmyelinated ventral root afferents, a projection into the segmental dorsal root was found. The majority of those fibres (about two‐thirds) are primary afferent neurones innervating the pia mater. Some of these units had a small spot‐like receptive field and responded to mechanical stimuli such as pressure and stretch of the root. They did not have axon projections in a peripheral nerve. 5. A few (5%) unmyelinated ventral root fibres are collateral branches of normal primary afferents projecting through the dorsal root. These trifurcating neurones are a small population which make up only some 0.5% of all dorsal root ganglion cells. The functional significance of this population too is unknown. 6. For none of the fibres that projected into both dorsal and ventral root was there positive evidence for the existence of looping axons that merely make a detour into one of the roots. Although the existence of loops cannot completely be excluded, our evidence suggests that they can constitute at most 5% of the unmyelinated ventral root afferents.
Activation of neurohypophysial vasopressin release by Ca2+ influx and intracellular Ca2+ accumulation in the rat.
Authors: Shibuki K
Published: December 2014

1. Isolated rat neurohypophyses were stimulated electrically in an in vitro perifusion system. A Ca2(+)‐sensitive microelectrode was placed in the centre of each neurohypophysis and [Ca2+]o decrease evoked by the stimulation were determined. 2. In neurohypophyses injected with Fura‐2 AM (acetoxymethyl ester), increases and decreases in fluorescence excited at 340 and 380 nm, respectively, were evoked by stimulation. The time course of the fluorescence changes was similar to that of [Ca2+]o decreases, suggesting that the [Ca2+]o changes mirrored [Ca2+]i increases. 3. Calcium influx into neurosecretory axons and terminals was estimated as the difference in [Ca2+]o decrease rates immediately before and after train pulse stimulation. 4. Vasopressin release from the neurohypophysis, measured by specific radioimmunoassay, was facilitated by stimulation in parallel with a parameter of [Ca2+]o decrease multiplied by Ca2+ influx. 5. The O2 consumption rate, estimated as rate of PO2 decrease in the tissue, was facilitated by stimulation in parallel with [Ca2+]o decreases. 6. Possible calcium‐dependent mechanisms of vasopressin release, and the energy‐dependent step of the release by Ca2+, are discussed.
Properties of enzymatically isolated skeletal fibres from mice with muscular dystrophy.
Authors: Head S I , Stephenson D G , Williams D A
Published: December 2014

1. Single intact muscle fibres were enzymatically isolated from the skeletal muscles of the dystrophic mouse 129/ReJ dy/dy and were subjected to a range of physiological interventions. 2. Electrophysiological measurements, diffusion of injected dyes (Lucifer Yellow), microdissection and general appearance in the light microscope have shown that the majority of skeletal fibres isolated from the soleus and extensor digitorum longus (EDL) of adult dystrophic mice (10‐14 weeks old) had gross morphological abnormalities. These abnormalities ranged from simple branching of the fibre to interconnections of many fibre branches which form a complex syncitium. 3. Segments from fibres of normal appearance and from fibres with morphological deformities were chemically skinned with Triton X‐100 and activated in Ca2(+)‐ and Sr2(+)‐buffered solutions. The different characteristics of the Ca2(+)‐ and Sr2(+)‐activation curves were also used to identify the fibre type. 4. Gross morphological abnormalities were observed both in fibres which had predominantly slow‐twitch and fast‐twitch characteristics. 5. A new group of fibres was found to exist in the soleus muscle of dystrophic animals and represented about 18% of the entire soleus fibre population. This group of fibres had predominantly fast‐twitch characteristics and some of these fibres were also grossly malformed. 6. The activation characteristics of individual branches from the same complex syncitium were similar, indicating that the contractile and regulatory proteins were of one type in one syncitium. 7. Chemically skinned segments from malformed fibres which included a major deformity between the points of attachment were generally unable to sustain near‐maximal forces. 8. The proportion of malformed fibres which remained intact decreased markedly after prolonged tetanical stimulation of the intact muscle. This strongly suggests that malformed fibres are also functionally weak and prone to progressive damage when stimulated within the intact muscle. 9. The presence in large proportions of fibres with gross morphological abnormalities may explain the symptoms of severe and progressive muscle weakness and muscle loss which are apparent in the 129/ReJ dy/dy mice and possibly even in the human dystrophies such as Duchenne muscular dystrophy.
Effect of lowered extracellular pH on Ca2(+)‐dependent K+ currents in type I cells from the neonatal rat carotid body.
Authors: Peers C
Published: December 2014

1. The whole‐cell configuration of the patch‐clamp technique was used to record K+ currents from type I cells enzymatically dispersed from the neonatal rat carotid body. The current‐voltage (I‐V) relationship for the K+ currents showed a prominent, outward shoulder at test potentials of between +10 and +30 mV. 2. The shoulder of the I‐V curve could be enhanced by raising extracellular Ca2+ concentration or by bath application of 5 microM‐Bay K 8644. It could also be suppressed by bath application of 100 microM‐Cd2+ or 5 microM‐methoxyverapamil (D600), indicating that a large component of the K+ current in these cells was activated by an influx of Ca2+ through its own channels during cell depolarization. 3. Potassium currents were also reversibly suppressed by 8 nM‐charybdotoxin but unaffected by 100 nM‐apamin, suggesting that the Ca2(+)‐dependent K+ current was carried through large or intermediate conductance Ca2(+)‐activated K+ channels. 4. Lowering the pH of the bathing medium from 7.40 to 7.00 reversibly reduced the K+ current amplitudes, and suppressed the shoulder normally seen in the I‐V relationship. This effect was enhanced in the presence of 5 microM‐Bay K 8644 and abolished in the presence of 5 microM‐D600. 5. It is concluded that the Ca2(+)‐dependent K+ channels of type I carotid body cells are selectively suppressed by extracellular acidity. Possible mechanisms underlying this effect, and its role in excitation of the carotid body are discussed.
Regulatory pathways for the stimulation of canine tracheal ciliary beat frequency by bradykinin.
Authors: Wong L B , Miller I F , Yeates D B
Published: December 2014

1. The effects of bradykinin, a potent inflammatory nanopeptide, on tracheal ciliary beat frequency in vivo were investigated using barbiturate‐anaesthetized beagles. Tracheal ciliary beat frequency was measured using heterodyne mode correlation analysis laser light scattering, a technique that does not require surgical intervention. 2. Aerosolized 10(‐5) M‐bradykinin in 0.9% saline administered for 3 min to eight barbiturate‐anaesthetized beagles stimulated tracheal ciliary beat frequency from the baseline of 5.3 +/‐ 0.1 Hz to a maximum of 16.6 +/‐ 2.0 Hz, 8 min after aerosol delivery, and ciliary beat frequency remained above baseline for the following 35 min. 3. Intravenously injected hexamethonium bromide, ipratropium bromide or indomethacin did not change baseline tracheal ciliary beat frequency. That down‐regulation of ciliary beat frequency below baseline values was not observed with either the neural or the cyclooxygenase blocking agents suggests that neither of these pathways is involved in the maintenance of the observed basal ciliary beat frequency. 4. Bradykinin‐induced stimulation of tracheal ciliary beat frequency is blocked by hexamethonium bromide, ipratropium bromide or indomethacin. These data suggest that the stimulation of ciliary beat frequency by bradykinin acts through both cellular cyclooxygenase and parasympathetic pathways in series.
On the presynaptic action of baclofen at inhibitory synapses between cultured rat hippocampal neurones.
Authors: Harrison N L
Published: December 2014

1. (‐)Baclofen reduces inhibitory postsynaptic potentials (IPSPs) and the associated synaptic currents (IPSCs) at inhibitory GABAergic synapses between cultured rat hippocampal neurones. The reversal potential for the IPSC is unaltered. 2. The effect of (‐)baclofen is concentration dependent; the EC50 for (‐)baclofen is approximately 5 microM. 3. Statistical analyses of the amplitude fluctuations of the IPSC in the presence of (‐)baclofen suggested a presynaptic location for the depression of synaptic transmission by (‐)baclofen. In control experiments, lowering extracellular Ca2+ produced similar effects. (‐)Baclofen has no detectable postsynaptic actions in these cultured neurones. 4. Phaclofen (0.2‐0.5 mM) increases IPSC amplitude but does not significantly block the depressant effect of (‐)baclofen on synaptic transmission. 5. The effect of (‐)baclofen is not blocked by pertussis toxin pre‐treatment. 6. It is concluded that (‐)baclofen acts presynaptically to reduce the release of GABA. The mechanism by which release is reduced may involve a phaclofen‐insensitive GABAB receptor.
Serotonin‐mediated inhibitory postsynaptic potential in guinea‐pig prepositus hypoglossi and feedback inhibition by serotonin.
Authors: Bobker D H , Williams J T
Published: December 2014

1. Intracellular recordings were made from neurones of the nucleus prepositus hypoglossi (PH) in slices of guinea‐pig brain. Focal stimulation evoked an inhibitory postsynaptic potential (IPSP) that was typically 10‐25 mV in amplitude and 1 s in duration. The IPSP reversal potential showed a Nernstian dependence on the external potassium concentration ([K+]o). 2. Spiperone blocked the IPSP with an IC50 of 40 nM, while ketanserin and (‐)sulpiride had no effect. Cocaine (1 microM) prolonged the IPSP half‐duration by 157%, and increased the amplitude by 28%. 3. 5‐Hydroxytryptamine (5‐HT, serotonin) hyperpolarized PH cells with an EC50 of 8.5 microM in control, and 135 nM in cocaine (10 microM). 8‐Hydroxy‐2‐(di‐n‐propylamino)‐tetralin (8‐OH‐DPAT) also hyperpolarized PH cells with an EC50 of 16 nM, although the maximal effect was only 81% of the maximum 5‐HT hyperpolarization. Spiperone produced a parallel, right shift of the 5‐HT concentration‐response curve; Schild analysis gave a Kd of 10 nM. Application of 5‐HT to neurones voltage‐clamped near their resting potential (about ‐55 mV) caused an outward current and an increase in membrane conductance. 4. The amplitude of the IPSP was reversibly decreased by non‐hyperpolarizing concentrations of 5‐HT and by the 5‐HT1 receptor agonists 1‐(m‐trifluoromethylphenyl)piperazine (TFMPP) and 1‐(3‐chlorophenyl)piperazine (mCPP). The IC50 values for the latter two compounds were 50 nM and 1.5 microM, respectively; the maximal effect was a 90% inhibition. Neither compound affected the membrane potential nor changed the hyperpolarization induced by 5‐HT. Quipizine competitively antagonized TFMPP with an estimated Kd of 165 nM. 5. When trains of stimuli were applied, an inhibition of the IPSP was observed following the first stimulus. At a frequency of 1 Hz, the inhibition was approximately 75%. This frequency‐dependent ‘run‐down’ of the IPSP was markedly attenuated by pre‐treatment with TFMPP (1 microM). 6. It is concluded that the IPSP in PH cells is caused by 5‐HT acting on 5‐HT1A receptors to activate a potassium conductance. The release of 5‐HT can be inhibited by activation of a presynaptic 5‐HT1D receptor. This presynaptic receptor appears to be at least partly responsible for the run‐down phenomenon, and may be involved in the physiological regulation of 5‐HT synaptic transmission.
M1 and M2 muscarinic receptors mediate excitation and inhibition of guinea‐pig intracardiac neurones in culture.
Authors: Allen T G , Burnstock G
Published: December 2014

1. The effects of muscarine upon intracardiac neurones cultured from ganglia within the atria and interatrial septum of the newborn guinea‐pig heart were studied using intracellular recording techniques. 2. Muscarine applied to the neuronal soma typically produced a biphasic change in membrane potential which consisted of a small hyperpolarization followed by a depolarization. In addition, muscarine (0.01‐10 microM) inhibited the calcium‐dependent, after‐hyperpolarization (AHP) and greatly increased the number of action potentials that could be evoked by a given depolarizing current. 3. The hyperpolarization was associated with a decrease in input resistance and it reversed to become a depolarization at a potential of ‐86.5 mV. This response was antagonized by 4‐diphenylacetoxy‐N‐methyl‐piperidine (4‐DAMP; 100 nM) and AF‐DX 116 (500 nM), but was unaffected by pirenzepine (0.1‐5 microM). 4. Two types of slow depolarization were observed in the presence of muscarine. The most common was associated with an increase in input resistance in the potential range ‐70 to ‐40 mV. Pirenzepine (100 nM) selectively antagonized this response, 4‐DAMP (100 nM) similarly antagonized the response, but was non‐selective. AF‐DX 116 (0.5‐5 microM) showed no antagonist effect. The less common depolarization (5% of cells) had a long latency and was associated with a decrease in input resistance. 5. Muscarine reduced the duration of the action potential and inhibited the AHP. Cadmium chloride (100 microM) mimicked these actions of muscarine. Application of muscarine immediately following a train of action potentials did not inhibit the AHP, suggesting that muscarine did not directly inhibit the calcium‐activated potassium current (IK(Ca)). Muscarine‐induced depression of the slow AHP was antagonized by 4‐DAMP (100 nM) but was not antagonized by either pirenzepine (0.1‐0.5 microM) or AF‐DX 116 (0.5‐5 microM). 6. It is concluded that the muscarine‐induced depolarization of guinea‐pig intracardiac neurones results from reduction of a potassium conductance similar to the M‐conductance, through activation of M1 muscarinic receptors. The hyperpolarization results from an increase in potassium conductance, through activation of M2 muscarinic receptors.
Anaerobic energy production and O2 deficit‐debt relationship during exhaustive exercise in humans.
Authors: Bangsbo J , Gollnick P D , Graham T E , Juel C , Kiens B , Mizuno M , Saltin B
Published: December 2014

1. Eight subjects performed one‐legged, dynamic, knee‐extensor exercise, first at 10 W followed by 10 min rest, then at an intense, exhaustive exercise load (65 W) lasting 3.2 min. After 60 min recovery, exercise was performed for 8‐10 min each at 20, 30, 40 and 50 W. Measurements of pulmonary oxygen uptake, heart rate, blood pressure, leg blood flow, and femoral arterial‐venous differences of oxygen content and lactate were performed as well as determination of ATP, creatine phosphate (CP) inosine monophosphate (IMP) and lactate concentrations on biopsy material from the quadriceps muscle before and immediately after the intense exercise, and at 3, 10 and 60 min into recovery. 2. Individual linear relations (r = 0.95‐1.00) between the power outputs for submaximal exercise and oxygen uptakes (leg and pulmonary) were used to estimate the energy demand during intense exercise. Pulmonary and leg oxygen deficits determined as the difference between energy demand and oxygen uptake were 0.46 and 0.48 l (kg active muscle)‐1, respectively. Limb and pulmonary oxygen debts (oxygen uptake during 60 min of recovery ‐ pre‐exercise oxygen uptake) were 0.55 and 1.65 l (kg active muscle)‐1, respectively. 3. During the intense exercise, muscle [ATP] decreased by 30% and [CP] by 60% from resting concentrations of 6.2 and 22.4 mmol (kg wet wt)‐1, respectively, and [IMP] increased to 1.1 mmol (kg wet wt)‐1. Muscle [lactate] increased from 2 to 28.1 mmol (kg wet wt)‐1, and the concomitant net lactate release was 14.8 mmol (kg wet wt)‐1 or about 1/3 of the total net lactate production. During recovery 70% of the accumulated lactate was released to the blood, and the nucleotides and CP returned to about 40 and 85% of pre‐exercise values at 3 and 10 min of recovery, respectively. 4. Total reduction in ATP and CP (and elevation of IMP) during the intense exercise amounted to 16.4 mmol ATP (kg wet wt)‐1, which together with the lactate production accounted for 83.1 mmol ATP (kg wet wt)‐1. In addition 6‐8 mmol ATP (kg wet wt)‐1 are made available related to accumulation of glycolytic intermediates including pyruvate (and alanine). Estimated leg oxygen deficit corresponded to an ATP production of 94.7 mmol ATP kg‐1; this value included 3.1 mmol kg‐1 related to unloading of HbO2 and MbO2.(ABSTRACT TRUNCATED AT 400 WORDS)
Kinetics of the conductance evoked by noradrenaline, inositol trisphosphate or Ca2+ in guinea‐pig isolated hepatocytes.
Authors: Ogden D C , Capiod T , Walker J W , Trentham D R
Published: December 2014

1. Guinea‐pig hepatocytes respond to noradrenaline (NA, 5‐10 microM) with a large membrane conductance increase to K+ and Cl‐. The response has a long initial delay (range 2‐30 s). Following the delay, the K+ conductance (studied in Cl(‐)‐free solutions) rises quickly to a peak in 1‐2 s and is maintained in the continued presence of NA, though often with superimposed oscillations of conductance. The roles of intracellular Ca2+ and D‐myo‐inositol 1,4,5‐trisphosphate (InsP3) in this complex response have been investigated by rapid photolytic release of intracellular Ca2+ (from Nitr5‐Ca2+ buffers) or InsP3 from ‘caged’ InsP3. 2. A rapid increase of intracellular [Ca2+] produced an immediate membrane conductance increase which rose approximately exponentially to a new steady level, consistent with a direct activation of Ca2(+)‐dependent ion channels. 3. Following a pulse of InsP3, conductance rose after a brief delay (range 70‐1500 ms) which was shortest at high [InsP3] or if the initial cytosolic [Ca2+] had been raised above normal levels. The maximum conductance produced by InsP3 was similar in each cell to the peak recorded with NA and could be evoked by InsP3 concentrations of 0.5‐1 microM. 4. The rates of rise of conductance increased with InsP3 concentration in the range 0.25‐12.5 microM (range 10‐90%, rise times 90‐1000 ms), indicating that InsP3‐evoked Ca2(+)‐efflux from stores increases with InsP3 concentration in this range. 5. Photochemically released InsP3 and Ca2+ activate at physiological concentrations the same membrane conductances as NA. The results indicate that the long initial delay in NA action occurs prior to or during generation of InsP3. The mechanism of the delay and the subsequent apparently all‐or‐none conductance increase during NA action are discussed in terms of the high co‐operativity in InsP3 and Ca2+ actions and an additional positive feedback step. 6. Evidence was found of a negative interaction between [Ca2+] and InsP3‐evoked Ca2+ release. The time course of the recovery of InsP3‐evoked Ca2+ release following a rise of cytosolic [Ca2+] suggests that this interaction may be important in regulating oscillatory responses of [Ca2+] during hormonal stimulation of guinea‐pig hepatocytes.
Prolonged muscle vibration reducing motor output in maximal voluntary contractions in man.
Authors: Bongiovanni L G , Hagbarth K E , Stjernberg L
Published: December 2014

1. We observed in a previous study on the human foot dorsiflexor muscles that the fatigue‐induced decline in motor output during sustained maximal voluntary contractions (MVCs) was temporarily counteracted during the initial phase of superimposed high‐frequency (150 Hz) muscle vibration, whereas prolonged muscle vibration seemed to accentuate the fatigue‐induced decline in gross EMG activity and motor unit firing rates. A more extensive investigation of this late effect of muscle vibration on MVCs was performed in the present study. 2. Prolonged periods of superimposed muscle vibration caused a reduction of EMG activity, motor unit firing rates and contraction force in both intermittent and sustained MVCs. This vibration‐induced effect had the following main characteristics: (i) it developed slowly during the course of about 1 min of sustained vibration and subsided within 10‐20 s after the end of vibration; (ii) it was much more pronounced in some subjects than in others (not age‐dependent) and it was accentuated by preceding muscle exercise; (iii) it affected primarily the subject's ability to generate and/or maintain high firing rates in high‐threshold motor units. 3. Since the effect developed while vibration at the same time exerted a tonic excitatory influence on the alpha‐motoneurone pool (as evidenced by the presence of a tonic vibration reflex) it is argued that the vibration‐induced suppression of motor output in MVCs probably does not depend on alpha‐motoneurone inhibition, but on a reduced accessibility of these neurones to the voluntary commands. It is suggested that contributing mechanisms might be vibration‐induced presynaptic inhibition and/or ‘transmitter depletion’ in the group Ia excitatory pathways which constitute the afferent link of the gamma‐loop.
Inward rectification in neonatal rat spinal motoneurones.
Authors: Takahashi T
Published: December 2014

1. Inward rectifying currents were recorded, using tight‐seal, whole‐cell voltage‐clamp methods, from motoneurones visually identified in thin slices of neonatal rat spinal cord. 2. When motoneurones were hyperpolarized from holding potentials near the resting potential (‐60 to ‐70 mV), a slow inward‐going current was recorded. After the hyperpolarizing command pulses, inward tail currents were recorded. Amplitudes of the inward current at the end of hyperpolarizing pulses as well as those of the tail current increased non‐linearly with the membrane hyperpolarization, showing an inward rectification in the current‐voltage relation. 3. Neither the amplitude nor the kinetics of the inward rectifying current (IIR) was appreciably affected by replacement of extracellularly Ca2+ with Mg2+ combined with the application of tetrodotoxin (1 microM), tetraethylammonium (30 mM), and 4‐aminopyridine (4 mM). The current was relatively resistant to Ba2+, being only slightly suppressed at 2 but not at 0.2 mM. However, it was completely and reversibly abolished by Cs+ (2 mM). 4. When the external K+ concentration was raised, IIR was augmented. However, the activation curve of IIR constructed from relative tail current amplitudes in high K+ solutions was indistinguishable from that in normal solution. The chord conductance of IIR at various membrane potentials was similar for both normal and high K+ solutions. Thus the whole‐cell conductance of inward rectification in motoneurones depends on the membrane potential but not appreciably on the external K+ concentration ([K+]o). 5. The reversal potential of IIR was estimated by measuring the tail currents. In standard solution ([K+]o = 3 mM), the reversal potential was about ‐44 mV. Increasing [K+]o shifted the reversal potential toward positive potentials by 22 mV for a tenfold change in potassium concentration. 6. A fivefold reduction in the external Na+ concentration shifted the reversal potential of IIR in a negative direction by about 7 mV, suggesting that Na+ may carry part of IIR. A fivefold reduction in external Cl‐ concentration shifted the reversal potential by about 2 mV but in a negative direction, the opposite of the expected shift in the Cl‐ equilibrium potential. 7. When external Cl‐ was substituted with isethionate or gluconate, IIR was markedly and reversibly suppressed. 8. It is concluded that in spinal motoneurones, IIR is carried by both K+ and Na+ ions and that external Cl‐ might be required to maintain the inward rectifier current.
The regulation of ATP‐sensitive K+ channel activity in intact and permeabilized rat ventricular myocytes.
Authors: Nichols C G , Lederer W J
Published: December 2014

1. In isolated rat heart ventricular myocytes exposed to 2 mM‐cyanide in the presence of 10 mM‐2‐deoxyglucose (complete metabolic blockade), there is a time‐dependent increase in ATP‐sensitive potassium (KATP) channel activity. The increase in KATP channel activity accompanies the decline of twitch amplitude. Channel activation and decline of the twitch amplitude precede the development of a ‘rigor’ contracture. 2. We measured KATP channel activity in permeabilized cells using the open‐cell attached (O‐C‐A) patch configuration (by establishing a cell‐attached patch and then permeabilizing the cell by exposure to saponin). The apparent ATP dependence of KATP channel activity could be described by a sigmoid curve with ki, ATP (ATP concentration required for half‐maximum inhibition of channel activity) = 122 microM and H (Hill coefficient) = 1.225. 3. In the O‐C‐A patch configuration, 10 mM‐creatine phosphate (CrP) decreased the apparent ki, ATP from 122 microM to about 10 microM, and the maximal activity (in zero ATP) was decreased to about 30% of the maximal activity in the absence of CrP. 4. In isolated inside‐out (I‐O) patches, ATP inhibited KATP channel activity at much lower [ATP] than in the O‐C‐A patch configuration (ki, ATP = 25 microM, H = 2). CrP was without effect on I‐O patches. 5. These results are consistent with the hypothesis that the difference in the ATP dependence of KATP channel activity in the O‐C‐A and I‐O patch configurations arises because of ATP consumption in the O‐C‐A patch configuration. The results suggest that hydrolysis of ATP to ADP by endogenous ATPases leads to the development of gradients of [ATP] and [ADP] between the bath and the ‘inside’ of the open cell. By re‐phosphorylating ADP, CrP is able to dissipate these gradients, revealing the ‘true’ ATP dependence of channel activity, which is the same as that in the I‐O patch configuration. 6. In order to estimate the contribution of KATP channel activity to the rat cardiac action potential at different [ATP] we have made the following measurements. Using electrodes of resistance 2‐8 M omega the density of KATP channels was 10.3 +/‐ 0.1 channels per patch (n = 162).(ABSTRACT TRUNCATED AT 400 WORDS)
An intracellular study of grafted and in situ preoptic area neurones in brain slices from normal and hypogonadal mice.
Authors: Hodgkiss J P , Kelly J S
Published: December 2014

1. Intracellular recordings have been obtained from forty‐one preoptic area (POA) neurones at times up to 14 months after they were grafted into the third ventricle of the mouse. Thirty‐one neurones were in grafts from hypogonadal (hpg) mice in which a reversal of the hypogonadism was seen (responders), six were in grafts from hpg mice in which no such reversal occurred (non‐responders) and four were in grafts from normal mice. 2. The grafted neurones had a mean resting potential (Em) of ‐57 mV, a mean apparent input resistance (Rm) of 136 M omega and a mean membrane time constant (tau m) of 7.7 ms. The slopes of the current‐voltage (I‐V) relations were linear. Approximately a quarter of neurones in responders fired action potentials spontaneously either singly or in bursts. Such activity could underlie the release of gonadotrophin hormone‐releasing hormone (GnRH) which is known to occur from such grafts. 3. Two types of response were seen when these neurones were depolarized to firing threshold from Em, in one group a single action potential was discharged; in the other group one or more action potentials arising from a transient, slowly rising and falling depolarization (low‐threshold response, LTR) was recorded. Some cells in the former category exhibited a LTR when depolarized from a potential more negative than Em. 4. The commonest response to stimulation of the median eminence in responders was an EPSP either alone or in combination with an IPSP. Antidromic action potentials were seen in four neurones and in two of these cells excitatory synaptic inputs could be demonstrated when the host hypothalamus adjacent to the graft was stimulated. It is suggested that these responses may represent activation of an afferent input from the host to neurones in the graft. 5. The morphology of neurones in POA grafts was determined by intrasomatic injection of horseradish peroxidase (HRP). A variety of profiles were seen and although some neurones extended over distances of up to 635 microns and branched extensively only one appeared to enter the host tissue at the ventrolateral edge of the graft. 6. A comparison was made between grafted POA neurones and cells in the medial preoptic area (MPOA), a region which constituted a significant component of the grafted tissue. No significant difference was noted between neurones in the graft and neurones in the MPOA in terms of their passive membrane properties. With regard to the active properties MPOA neurones could also be classified according to whether or not a LTR was elicited when the neurone was depolarized from Em. The major difference between the grafted neurones and those in the MPOA lay in the proportion of cells which exhibited a LTR under such conditions, being significantly greater in the latter group.
Modulation of Ca2+ transients and contractile properties by beta‐adrenoceptor stimulation in ferret ventricular muscles.
Authors: Okazaki O , Suda N , Hongo K , Konishi M , Kurihara S
Published: December 2014

1. The mechanism of modulation of Ca2+ transients and contraction by beta‐adrenoceptor stimulation was studied in ferret ventricular muscles using aequorin to measure intracellular Ca2+. 2. Peaks of tension and light transients were increased by isoprenaline (10(‐9) ‐ 5 x 10(‐7) M) which also abbreviated their time courses. 3. Time‐to‐peak tension was significantly shortened by 5 x 10(‐9) M‐isoprenaline and time‐to‐peak light was abbreviated by 10(‐9) M‐isoprenaline. 4. The time for the light to decay was shortened at 10(‐9) M‐isoprenaline. However, a higher concentration of isoprenaline (10(‐8) M) was required for significant shortening of the half‐relaxation time (TR50). 5. When isoprenaline was removed and beta‐blocker (bupranolol, 1 microM) was applied, the time course of the light transients recovered but the time course of relaxation did not recover. 6. The relationship between [Ca2+]i and tension in tetanic contraction produced in the presence of ryanodine (5 microM) was shifted to the right by isoprenaline (10(‐8) M). This was recovered by the replacement of isoprenaline with bupranolol (1 microM). 7. Isoprenaline (10(‐7) M) added to the solution containing 20 mM [Ca2+]O and Bay K 8644 (1 microM), which produced maximal tension, caused a large light signal and enhancement of the initial phasic tension in tetanic contraction. However, the replacement of isoprenaline with bupranolol after immersing the preparation in 20 mM [Ca2+]O solution with Bay K 8644 and isoprenaline, did not significantly change the tension level, although the light signal decreased. Similar results were obtained in the ventricular muscle of young rats. 8. These results suggest that the dose dependence of modulation of the contractile element and sarcoplasmic reticulum (SR) by beta‐adrenoceptor stimulation differs, and that additional factors, other than the faster Ca2+ uptake by SR and the decrease in Ca2+ sensitivity of the contractile element, might be involved in the shortening of the half‐relaxation time by beta‐adrenoceptor stimulation. In addition, beta‐adrenoceptor stimulation does not produce a marked change in the maximal tension level.
Effects of carbonic anhydrase inhibitors on contraction, intracellular pH and energy‐rich phosphates of rat skeletal muscle.
Authors: Geers C , Gros G
Published: December 2014

1. The effects of carbonic anhydrase inhibitors on contractile parameters, intracellular pH (pHi) and energy‐rich phosphates were studied in isolated rat soleus and extensor digitorum longus (EDL) muscles. 2. The muscles were incubated either in Ringer solutions (95% O2/5% CO2 = control) or in solutions to which one of the inhibitors, 5 X 10(‐4) M‐chlorzolamide or 10(‐2) M‐NaCNO, had been added. Muscles were stimulated directly and contracted under isometric conditions. 3. Compared with control muscles, both inhibitor‐treated muscles showed a significantly decreased tetanic force and an increased half‐relaxation time of twitches and tetani. Chlorzolamide increased time‐to‐peak in both muscles. Cyanate decreased isometric twitch force in both muscles. 4. Both inhibitors decreased pHi in both muscles; chlorzolamide by 0.1 unit, cyanate by 0.4 unit in soleus and by 0.8 unit in EDL. 5. Chlorzolamide increased the concentrations of creatine and inorganic phosphate (Pi) in soleus (the effect of chlorzolamide was not studied in EDL). Cyanate caused these same changes in soleus as well as EDL and in addition decreased the concentrations of ATP and phosphocreatine in soleus and EDL. 6. In muscles acidified by either low external HCO3‐ (2 mM) or by elevated PCO2 (30% CO2 in the gas phase) in the bath, decreases in isometric force and increases in half‐relaxation time of tetani were observed. In addition there were increases in muscle Pi. These effects were more pronounced with 30% CO2 than with 2 mM‐HCO3‐. 7. Neither acidifying solutions prolonged either half‐relaxation time or time‐to‐peak of twitches. 8. We conclude that carbonic anhydrase inhibition exerts its effect (a) on isometric tension at least partly via an elevated Pi (perhaps in combination with lowered pHi); (b) on the half‐relaxation time of tetani by means of lowered pHi and elevated concentration of Pi; (c) on relaxation and time‐to‐peak of twitches by some unknown mechanism, neither directly by a change in pHi nor in Pi.