bluuebunny/crossref_metadata_2025 huggingface dataset:
Potassium and chloride conductances in rat Leydig cells: effects of gonadotrophins and cyclic adenosine monophosphate.
Authors: Duchatelle P , Joffre M
Published: December 2014

1. The effects of gonadotrophins (luteinizing hormone and human chorionic gonadotrophin) and cyclic AMP on ionic conductances were investigated using the tight‐seal whole‐cell recording technique in Leydig cells freshly isolated from nature rat testis by enzymatic treatment. 2. In resting cells, the predominant ionic conductance is a voltage‐dependent K+ conductance resembling the delayed rectifier K+ conductance of T‐lymphocytes. This conductance is characterized by: (1) a time‐dependent inactivation for potentials more positive than +20 mV, (2) a reversal potential near ‐65 mV, (3) a sensitivity to intracellular Cs+, and (4) a sensitivity to extracellular TEA and 4‐aminopyridine. 3. A Cl‐ conductance is also present resembling the Cl‐ background conductance in squid axons and heart cells. In resting cells, this conductance contributes only a small component of the total outward current obtained with depolarizing pulses. 4. Gonadotrophins (human chorionic gonadotrophin, porcine luteinizing hormone and ovine luteinizing hormone) have little effect on the K+ conductance. They transiently increase a Cl‐ conductance after a delay of up to 30 s. This response does not occur if the hormones are applied late in the whole‐cell recording. Gonadoliberine (GnRH) does not affect the Cl‐ or K+ conductance. 5. Internal cyclic AMP (100 microM) mimics all these effects while internal application of a GTP‐ATP mixture induces a similar response, which is, however, sustained rather than transient. 6. The Cl‐ conductance was studied quantitatively with a GTP‐ATP internal solution. This conductance is activated by depolarizing voltage steps to test potentials of ‐40 mV or more. Under these conditions, the instantaneous current observed as soon as the depolarizing pulse is applied displays outward rectification and reverses near ECl. During the pulses, a strong inactivation is observed for potentials greater than +40 mV. This conductance is independent of external and internal calcium. 7. It is concluded that the gonadotrophins act through a cyclic AMP‐dependent process to activate a Cl‐ conductance. This conductance is different to the hyperpolarization‐activated Cl‐ conductance and the calcium‐activated Cl‐conductance also present in the membrane of resting cells.
Synaptic excitation of inhibitory cells by single CA3 hippocampal pyramidal cells of the guinea‐pig in vitro.
Authors: Miles R
Published: December 2014

1. In simultaneous recordings from pairs of neurones in hippocampal slices from guinea‐pigs, single action potentials fired by CA3 pyramidal cells could initiate inhibitory postsynaptic potentials (IPSPs) in nearby pyramidal cells. 2. The latencies of these IPSPs could be as short as 3 ms. However, they were mediated disynaptically via chemical, excitatory synapses, since inhibitory coupling was suppressed by an excitatory amino acid antagonist. 3. The properties of excitatory synapses made onto inhibitory cells were examined to assess the basis for this strong coupling. Inhibitory cells were identified either by showing that they inhibited another cell or by their characteristic firing pattern. 4. Excitatory postsynaptic potentials (EPSPs) elicited by single pyramidal cell action potentials had a mean amplitude of 1‐4 mV and a time to peak of 1.5‐4 ms. In most cases they decayed with a time constant similar to that of the inhibitory cell membrane. 5. EPSP amplitude increased with hyperpolarization of the postsynaptic membrane. Membrane polarization had little effect on EPSP shape. 6. EPSPs fluctuated in amplitude and transmission sometimes failed, suggesting transmission was quantal and that few quanta were released. 7. When presynaptic cells were made to fire bursts of action potentials, EPSPs in inhibitory cells were initially potentiated. 8. EPSPs could cause inhibitory cells to fire. The interval between pre‐ and postsynaptic spikes could be as short as 2.5 ms and the probability of spike transmission could be as high as 0.6. Some inhibitory cells which received feedback excitation were also excited in feedforward fashion by mossy fibre stimuli. 9. One pyramidal cell could activate several disynaptic inhibitory pathways terminating on another pyramidal cell. This suggests that excitatory synapses made by pyramidal cell axon collaterals onto inhibitory cells are divergent. 10. This strong, divergent excitation of inhibitory cells ensures recurrent inhibition is sufficiently widespread, rapid and potent to control the spread of activity by recurrent excitatory connections between CA3 pyramidal cells.
Reflex coronary vasodilation evoked by chemical stimulation of cardiac afferent vagal C fibres in dogs.
Authors: Clozel J P , Pisarri T E , Coleridge H M , Coleridge J C
Published: December 2014

1. Veratridine injected into the coronary circulation stimulates afferent vagal endings in the heart to evoke bradycardia and systemic hypotension (Bezold‐Jarisch reflex, coronary chemoreflex) and coronary vasodilation. We have examined certain features of the reflex coronary vasodilator response in anaesthetized dogs. 2. When the circumflex coronary artery was perfused at constant pressure (100 mmHg), injection of veratridine (0.3 micrograms kg‐1) into the anterior descending artery decreased blood pressure and heart rate, and increased circumflex blood flow by 54%; when heart rate was kept constant, circumflex flow increased by 57%. The increase in circumflex flow was reduced 63% by atropine, and finally abolished by phentolamine. 3. During severe coronary underperfusion (perfusion pressure 45 mmHg), veratridine still increased coronary flow by 35%, an increase amounting to 24‐64% of the coronary vascular reserve. Flow increased in all layers of the myocardium, but the relative distribution of flow between subendocardial and subepicardial layers was unaltered. 4. Veratridine stimulates both mechanosensitive and chemosensitive cardiac endings. Stimulating chemosensitive afferents selectively by injecting capsaicin (1.5 micrograms kg‐1) into the anterior descending artery decreased blood pressure and heart rate, and increased circumflex flow by 50% (and by 36% when heart rate was kept constant). 5. In ten of fifteen dogs, veratridine and capsaicin still evoked coronary vasodilatation when vagal A fibres were blocked selectively by cooling to 7.5 degrees C, the increase in coronary flow averaging 45% of that at 37 degrees C. All responses were abolished by cooling to 0 degrees C. 6. We conclude that coronary vasodilatation can be evoked by selective stimulation of cardiac chemosensitive vagal C fibres, although the coronary vasodilation of the veratridine‐induced Bezold‐Jarisch reflex may be due to stimulation of both mechanosensitive and chemosensitive C fibres. We speculate that during periods of coronary underperfusion ischaemic stimulation of chemosensitive vagal C fibres evokes a reflex dilatation of the coronary vascular bed that supplements the dilatation dependent upon autoregulatory mechanisms.
Voltage‐dependent currents in isolated cells of the frog retinal pigment epithelium.
Authors: Hughes B A , Steinberg R H
Published: December 2014

1. Retinal pigment epithelial (RPE) cells were isolated enzymatically from bullfrog retinae. The patch‐clamp technique was employed to investigate whole‐cell currents under voltage‐clamp conditions. 2. Isolated RPE cells were columnar or cuboidal in form, often with long processes protruding from the apical surface. Distinct apical and basal membrane domains were maintained for several hours following isolation. 3. The mean membrane capacitance was 62 pF. The resting potential averaged ‐30 mV, but it was as high as ‐75 mV in some cells. 4. Three voltage‐dependent currents were observed: a time‐independent and inwardly rectifying current and two time‐dependent outwardly rectifying currents that had distinct kinetic properties. 5. Voltage pulses from a holding potential of ‐70 mV to potentials ranging from ‐30 to ‐120 mV produced membrane currents that were essentially time independent. The I‐V relationship in this voltage range depended on the resting potential. It was usually inwardly rectifying in cells with resting potentials negative to about ‐50 mV, but tended to be linear in cells with more positive potentials. Three observations strongly suggested that the inwardly rectifying current is carried by K+. First, increasing the extracellular K+ concentration [( K+]) from 2 to 112 mM shifted the zero‐current potential of the I‐V relationship in the positive direction from an average value of ‐60 mV to 0 mV. Second, the addition of the K+ channel blockers Ba2+ (2 mM) or Cs+ (5 mM) to the extracellular solution inhibited a major component of the inwardly rectifying current. Finally, the reversal potential (Vr) of the Ba2(+)‐sensitive current averaged ‐90 mV, near the K+ equilibrium potential (EK). 6. In approximately 50% of the cells, depolarizing voltage pulses to potentials more negative than ‐30 mV evoked an outward current that resembled the delayed rectifier present in other non‐excitable cells. It activated with sigmoidal kinetics in less than 100 ms following a brief delay and then declined exponentially with a time constant of approximately 1 s. The peak chord conductance associated with this current was half‐maximal at +14 mV. Several observations indicated that this outwardly rectifying current is carried primarily by K+: its Vr closely matched EK over a wide range of extracellular [K+]; it was inhibited 80% by exposure to the K+ channel blockers 4‐aminopyridine (1 mM) and tetraethylammonium (20 mM); and it was abolished by intracellular dialysis with a K(+)‐free solution.(ABSTRACT TRUNCATED AT 400 WORDS)
Characteristics of chloride currents activated by noradrenaline in rabbit ear artery cells.
Authors: Amédée T , Large W A , Wang Q
Published: December 2014

1. Responses to noradrenaline were studied in isolated rabbit ear artery cells with the nystatin method of whole‐cell patch‐clamp recording. With this technique it was possible to obtain reproducible responses to noradrenaline which was not possible with traditional whole‐cell recording. 2. With NaCl as the major constituent of the bathing solution (potassium‐free pipette and external solutions) the reversal potential (Er) of the noradrenaline‐evoked current was about 0 mV. When external chloride was replaced by thiocyanate, iodide, nitrate and bromide, Er was shifted to more negative potentials which indicates that a chloride conductance increase contributes to the current activated by noradrenaline. 3. When sodium was substituted by Tris, N‐methyl‐D‐glucamine, choline or barium, Er of the noradrenaline‐evoked current did not alter. This result suggests that a cation conductance is not implicated in the response to noradrenaline recorded with the nystatin method of whole‐cell recording. 4. The chloride current activated by noradrenaline was blocked by the selective alpha 1‐adrenoceptor antagonist prazosin but was not affected by the alpha 2‐adrenoceptor antagonist yohimbine. 5. When cells were exposed to zero calcium bathing solutions the amplitude of the current elicited by noradrenaline was unaffected when measured within 1‐2 min in zero calcium conditions. Continued exposure to 0 Ca + 1 mM‐EGTA solution reversibly abolished the chloride current to noradrenaline. 6. In the presence of caffeine, which releases Ca2+ from internal stores and itself induced an inward current (at a holding potential of ‐50 mV), noradrenaline did not elicit a current. These data suggest that the chloride current evoked by noradrenaline results from an increase in intracellular concentration of calcium derived from internal stores. 7. The chloride channel blocking agents 4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid (DIDS; 0.5 mM) and furosemide (0.5 mM) produced partial reduction of the noradrenaline‐evoked chloride current whereas 4‐acetamido‐4'‐isothiocyanatostilbene‐2,2'‐disulphonic acid (SITS), anthracene‐9‐carboxylic acid (A‐9‐C) and picrotoxin were ineffective in concentrations of up to 0.5 mM. However DIDS and furosemide were non‐selective blockers as both agents were more effective against the adenosine triphosphate‐induced cation current.
On the localization of the stretch reflex of intrinsic hand muscles in a patient with mirror movements.
Authors: Matthews P B , Farmer S F , Ingram D A
Published: December 2014

1. The patient studied showed the typical mirror movements of the Klippel‐Feil syndrome. Earlier intensive electrophysiological analysis suggests that many of her corticospinal axons branch abnormally to supply motoneurones on both sides of the spinal cord. Thus, in her, a long‐latency reflex utilizing the motor cortex should manifest itself bilaterally. 2. EMG recordings were made simultaneously from the first dorsal interosseous (FDI) muscles of both hands while they were being voluntarily activated by the subject. The FDI of one hand was then briefly stretched by forcibly adducting the index finger. Similar but more limited studies were made using flexor pollicis brevis. 3. The reflex response of the stretched muscle consisted of a typical mixture of early (M1) and late (M2) components, with mean latencies of 32 and 49 ms respectively. 4. Unlike normal controls, the contralateral muscle responded on stretch of the ipsilateral muscle. However, its response consisted solely of a long‐latency reflex. This was comparable in size, latency and waveform to the ipsilateral late component. (Mean size, 84% of the ipsilateral M2 response; mean latency 46 ms, or 3 ms less than the ipsilateral response due to the absence of M1). 5. The short‐latency response did not spread to the homologous contralateral muscle even when it was large ipsilaterally. The long‐latency response elicited from FDI did not spread to the abductor digiti minimi muscle of either hand. 6. Reducing the duration of the stretch reduced the duration of the crossed response by an equivalent amount. Unloading the ipsilateral muscle produced a delayed reduction of EMG activity contralaterally. Thus her long‐latency pathway can act tonically as well as phasically. 7. These findings strongly support the hypothesis that delayed components of the human stretch reflex are relayed via the motor cortex and the corticospinal tract.
The frequency of isomerization‐like ‘dark’ events in rhodopsin and porphyropsin rods of the bull‐frog retina.
Authors: Donner K , Firsov M L , Govardovskii V I
Published: December 2014

1. The dark current and responses to dim flashes were recorded with the suction pipette technique from single rods in pieces of bull‐frog retina taken from either the dorsal porphyropsin or the ventral rhodopsin field. 2. The composition of visual pigment in the rods was determined by microspectrophotometry. Rods from the dorsal pieces contained 70‐88% porphyropsin523 mixed with rhodopsin502. The ventral rods contained almost pure rhodopsin, any possible admixture of porphyropsin being below the level of detectability (less than 5%). 3. In most cells, the responses to dim flashes were well fitted by a four‐stage linear filter model, with no systematic differences in the response kinetics of porphyropsin and rhodopsin rods. The amplitude of saturated responses varied between 8 and 55 pA and that of responses to single isomerizations between 0.4 and 3.5 pA. 4. In porphyropsin rods, discrete events similar to the response to one photoisomerization were clearly seen in complete darkness. The dark current amplitude histogram was fitted by a convolution of the probability densities for the Gaussian continuous noise component and the averaged dim‐flash response waveform. This allows estimation of the frequency and amplitude of discrete events and the standard deviation of the continuous component. The mean frequency of discrete dark events thus obtained from six porphyropsin cells was 0.057 rod‐1 s‐1 at 18 degrees C. 5. In rhodopsin rods, the dark current amplitude histogram appeared completely symmetrical, indicating that the frequency of discrete events must be lower than 0.005 rod‐1 s‐1 (except in one rod where it was 0.006 events rod‐1 s‐1). Per molecule of rhodopsin, the events are then at least 5 times rarer than reported for toad rhodopsin rods at the same temperature. 6. The low rate of isomerization‐like ‘dark’ events in bull‐frog rhodopsin rods shows, firstly, that results cannot be generalized across species even for rhodopsins which appear spectrally identical. Secondly, it suggests that these events need not (in an evolutionary sense) constitute an irreducible noise factor which must set the ultimate limit to the sensitivity of dark‐adapted vision. 7. The difference between porphyropsin and rhodopsin rods shows that, given (presumably) the same opsin, the pigment utilizing retinal2 and absorbing maximally at longer wavelengths produces more noise. The signal/noise ratio attained in the photoreceptor may be an important factor in the natural selection of visual pigments.
Nucleus tractus solitarius as mediator of evoked parabrachial cardiovascular responses in the decerebrate rabbit.
Authors: Paton J F , Silva‐Carvalho L , Thompson C S , Spyer K M
Published: December 2014

1. The present study has assessed the importance of neurones within the nucleus tractus solitarius (NTS) in mediating the cardiovascular response evoked from the parabrachial nucleus (PBN) in the decerebrate rabbit. Microinjection techniques were employed so that the magnitude of the circulatory responses elicited from the PBN could be compared before, and after, kainic acid or bicuculline were microinjected into restricted regions of the NTS. 2. Electrical stimulation of the PBN (both medial and lateral regions) evoked variable changes in heart rate, a pressor response, vasoconstriction in the hindlimb and an increase in renal sympathetic nerve activity. Glutamate injected into these regions of the PBN elicited a similar pattern of response except that a tachycardia was observed consistently. 3. Both electrical and chemical stimulation of restricted regions of the NTS evoked bradycardia and a depressor response together with an increase in femoral vascular conductance and an inhibition of activity in the renal nerve. 4. Chemical lesions placed in these regions of the NTS by microinjecting kainic acid were found to attenuate both the heart rate and arterial blood pressure responses elicited from sites in the medial and lateral PBN using either electrical or chemical stimulation. Equivalent effects were produced on microinjecting the GABAa receptor antagonist bicuculline into the NTS. 5. These data indicate that NTS neurones play a part in mediating the cardiovascular responses that are evoked from the PBN and suggest that the action of the PBN at the level of the NTS is mediated via a GABAergic mechanism.
Characteristics of miniature inhibitory postsynaptic currents in CA1 pyramidal neurones of rat hippocampus.
Authors: Ropert N , Miles R , Korn H
Published: December 2014

1. Recordings were made in vitro from chloride‐loaded CA1 rat hippocampal pyramidal neurones in the presence of tetrodotoxin (TTX) to examine miniature inhibitory postsynaptic currents (IPSCs). 2. Most spontaneous synaptic events recorded before TTX was applied, and all events that were resolved in the presence of TTX, were blocked by the GABAA receptor antagonist bicuculline. 3. At 25 degrees C, averaged miniature IPSCs had time to peak of about 3 ms and in most cases decayed with a single time constant close to 25 ms. 4. With a driving force for chloride ions between 70 and 80 mV, the mean miniature IPSC amplitude was 19.6‐27.9 pA, yielding a conductance of 258‐326 pS. The mean amplitude of unitary IPSCs recorded before TTX was applied was in the range of 31‐73 pA. 5. When intervals between miniature IPSCs were compared with an exponential distribution, there was an excess of events at intervals shorter than 5 ms. Some individual events appeared to represent the nearly simultaneous release of two inhibitory quanta. 6. Miniature IPSC amplitude distributions were better fitted with the sum of two Gaussians than with one Gaussian. The variance in amplitude of a single quantal event exceeded that of the baseline noise. 7. Comparison of the conductance changes corresponding to the first Gaussian distribution with single GABA channel data suggests that one inhibitory quantum opens twelve to twenty chloride channels and that GABA molecules bind once to a postsynaptic receptor.
Reflex inhibition of human soleus muscle during fatigue.
Authors: Garland S J , McComas A J
Published: December 2014

1. Human soleus muscles were fatigued under ischaemic conditions by intermittent stimulation at 15 Hz. When maximal voluntary plantarflexion was then attempted, the loss of torque was found to be associated with a reduction in voluntary EMG activity. 2. The decrease in EMG activity could not have been due to ‘exhaustion’ of descending motor drive in the central nervous system since fatigue had been induced by electrical stimulation of peripheral nerve fibres. Similarly, the decrease could not be explained by changes at the neuromuscular junction or muscle fibre membrane, since changes in the M wave (evoked muscle compound action potential) were relatively modest. 3. When the excitability of the soleus motoneurones was tested during fatigue, using the H (Hoffmann) reflex, it was found to be significantly reduced. Control experiments with ischaemia or electrical stimulation, but without fatigue, failed to demonstrate any significant effects on reflex excitability. 4. The findings in this study favour the concept of reflex inhibition of alpha‐motoneurones during fatigue.
Modulation of the [Ca2+] sensitivity of myosin phosphorylation in intact swine arterial smooth muscle.
Authors: Rembold C M
Published: December 2014

1. The [Ca2+] sensitivity of myosin light chain phosphorylation in vascular smooth muscle is dependent on the form of stimulation. Contractile agonist stimulation, when compared to high‐KCl depolarization, is associated with an increase in [Ca2+] sensitivity of phosphorylation. I evaluated potential mechanisms for this stimulus‐specific response by measuring aequorin‐estimated myoplasmic [Ca2+], myosin phosphorylation, and isometric stress in swine carotid media. 2. The relative [Ca2+] sensitivity of phosphorylation depended on the type of stimulus (ranked high to low sensitivity): contractile agonists (histamine, phenylephrine) = endothelin (sustained contraction) = combination of histamine and NaF greater than NaF alone = endothelin (initial contraction) = combination of histamine and depolarization = combination of NaF and depolarization greater than depolarization = Bay K 8644 = combination of depolarization and low‐dose phorbol diester. 3. Activation of L‐type Ca2+ channels with Bay K 8644 induced a [Ca2+] sensitivity of phosphorylation similar to depolarization, suggesting that any other effects of high KCl (such as cellular swelling) were not responsible for the low [Ca2+] sensitivity of phosphorylation. 4. The addition of either histamine or NaF (an activator of G proteins) to depolarized tissues produced similar increases in the [Ca2+] sensitivity of phosphorylation, suggesting that NaF (possibly by activation of a G protein) can mimic contractile agonist‐induced increases in the [Ca2+] sensitivity of phosphorylation. 5. Phorbol dibutyrate enhanced the contractile effect of depolarization, and this enhancement was primarily caused by increases in [Ca2+] rather than an alteration in the [Ca2+] sensitivity of phosphorylation. 6. These data suggest that the [Ca2+] sensitivity of phosphorylation in smooth muscle may be regulated by agonists (possible by G protein activation); however, the role of protein kinase C activation or depolarization induced Ca2+ compartmentalization requires further study.
Histamine and FLRFamide regulate acetylcholine release at an identified synapse in Aplysia in opposite ways.
Authors: Baux G , Fossier P , Tauc L
Published: December 2014

1. The effects of histamine and FLRFamide (Phe‐Leu‐Arg‐Phe‐NH2) on acetylcholine (ACh) release were studied in the buccal ganglion of Aplysia californica on an identified synapse (buccal ganglion inhibitory synapse, BGIS) involved in a small neuronal circuit controlling the feeding behaviour. The inhibitory postsynaptic current (IPSC) evoked by a presynaptic spike in the voltage‐clamped postsynaptic neurone was decreased by histamine and increased by FLRFamide. 2. Histamine and FLRFamide modified the amplitude of the presynaptic spike. To test if these drugs acted directly on presynaptic calcium influx, we evoked transmitter release by 3 s depolarizations of the presynaptic neurone (to +10 mV) under voltage clamp to avoid modifications of presynaptic membrane polarization induced by changes in presynaptic voltage‐dependent K+ and/or Na+ conductances. 3. Statistical analysis of this evoked long‐duration (3 s) induced postsynaptic current (LDIPSC) allowed us to calculate the amplitude and the decay time of the miniature postsynaptic current and consequently the number of quanta released by the presynaptic terminal. 4. The amplitude of the LDIPSC decreased during the 3 s presynaptic depolarization. This was not due to a lack of available transmitter, since LDIPSC amplitude could be maintained constant by a ‘clamp of the release of ACh’ which adequately depolarized the presynaptic neurone, but rather to changes in the calcium influx into the presynaptic neurone. 5. FLRFamide increased more the initial portions of the LDIPSC than the final portions. This effect of FLRFamide was only reduced and delayed by atropine or curare, antagonists of muscarinic‐like and nicotinic‐like autoreceptors previously demonstrated to be present at the same terminal. Activation of the nicotinic‐like receptors, which also increased transmitter release, induced a modification of the shape of the LDIPSC which was completely different from that due to FLRFamide. 6. Histamine decreased the amplitude of the LDIPSC. This effect was more pronounced at the beginning of the response. The effects of histamine were insensitive to curare and atropine, but were completely blocked by cimetidine, a specific histamine receptor antagonist. 7. The modifications of the shape and of the amplitude of the LDIPSC by FLRFamide and histamine suggested that these molecules alter presynaptic influx of calcium. This was confirmed by the analysis of calcium current recorded from the presynaptic neurone: the calcium inward current in the presynaptic neurone was increased by FLRFamide and reduced by histamine, whereas the activation of autoreceptors had no measurable effect on calcium current.(ABSTRACT TRUNCATED AT 400 WORDS)
Locations and properties of angiotensin II‐responsive neurones in the circumventricular region of the duck brain.
Authors: Matsumura K , Simon E
Published: December 2014

1. In brain slice preparations from the hypothalamus of domestic ducks, single‐unit activity was recorded extracellularly to investigate location and properties of angiotensin II (AngII)‐responsive neurones in various periventricular regions. 2. When exposing the slice to 10(‐7) M‐AngII in the perfusion medium, more than 65% of the neurones recorded in the subfornical organ (SFO) were activated (49 out of 75) and none inhibited. In the magnocellular (MC) region of the paraventricular nucleus (PVN) only four out of eighty‐one neurones were influenced by AngII; one was inhibited and three were activated. In the anterior third ventricle region (A3V) two out of twenty‐one neurones were activated by AngII. In the dorsal periventricular (PeV) region, one out of thirty‐seven neurones was activated and one inhibited. The changes in firing rate of AngII‐responsive neurones at comparable doses of AngII were generally large in the SFO and A3V but were small in neurones from the MC and PeV regions. 3. Analysis of AngII‐responsive SFO neurones consistently revealed a dose‐dependent stimulation with a threshold at 10(‐9) M‐AngII. The AngII antagonist 1Sar‐8Ile‐AngII (4 x 10(‐7) to 10(‐6) M) caused reversible, complete or partial suppression of responsiveness to 10(‐7) M‐AngII. Synaptic blockade with a medium low in Ca2+ and high in Mg2+ did not abolish AngII responsiveness in eight out of ten SFO neurones tested. 4. Angiotensin III affected neither AngII‐responsive nor AngII‐insensitive neurones. When eighteen AngII‐responsive neurones were exposed to hypertonic stimulation (+20 to +30 mosmol/kg) by adding NaCl to the perfusion medium, only one neurone was stimulated and two were inhibited. 5. The results indicate that: (a) the SFO is a specific target for circulating AngII; (b) although neurones in the A3V responsive to AngII are rare, the pronounced excitation of those which were found suggest that neurones in this region might serve as targets for AngII acting from the brain side; (c) neurones in the MC region do not seem to function as direct AngII targets; (d) neuronal AngII responsiveness in the duck's hypothalamus seems to be specific inasmuch as activation by AngII (i) is readily blocked by an AngII antagonist, (ii) cannot be induced by AngIII, and (iii) is not associated, as a rule, with responsiveness to hypertonic stimulation.
The effect of changes in adrenal blood flow on adrenal cortical responses to adrenocorticotrophin in conscious calves.
Authors: Jones C T , Edwards A V , Bloom S R
Published: December 2014

1. The effect of varying adrenal blood flow on the rate at which it was estimated that adrenocorticotrophin (ACTH) was presented to the adrenal gland was related to right adrenal cortisol output in conscious calves fitted with ‘adrenal clamps’. 2. Intra‐aortic infusions of endothelin at either 15.0 or 7.5 pmol min‐1 kg‐1 produced a substantial fall in right adrenal blood flow which was dose‐related over this range. There was an associated fall in right adrenal cortisol output and cortisol output was linearly related to estimated ACTH presentation to the gland over the whole range investigated. The changes in adrenal cortisol output were reflected by changes in the concentration of cortisol in the peripheral plasma, which could be attributed entirely to the fluctuations in adrenal cortisol output. 3. It is concluded that delivery of ACTH to the adrenal gland is flow dependent over the physiological range in these animals and that changes in adrenal cortical blood flow can therefore be expected to result in changes in adrenal output due to variations in the presentation rate of ACTH.
The inhibition of single N‐methyl‐D‐aspartate‐activated channels by zinc ions on cultured rat neurones.
Authors: Legendre P , Westbrook G L
Published: December 2014

1. Single channels activated by N‐methyl‐D‐aspartate (NMDA) were studied in outside‐out patches of cultured hippocampal neurones in the presence of glycine and absence of magnesium. The effects of the transition metal ions zinc and cadmium on NMDA channels were tested by placing the membrane patch at the mouth of one of an array of large barrelled flow pipes. 2. Amplitude histograms revealed several conductance levels between 5 and 45 pS with the majority of NMDA‐activated openings greater than 25 pS. Zinc (5‐100 microM) and cadmium (30‐100 microM) reduced the number of large conductance events in a voltage‐independent manner. Zinc (30 microM) reduced the large conductance openings by approximately 70‐80%. The small number of events under 20 pS precluded quantitative assessment of the effects of zinc and cadmium on these conductance levels. Zinc inhibition of the calculated macroscopic current due to NMDA‐activated channels could be fitted with a single binding site isotherm with an IC50 of 12 microM. 3. Zinc and cadmium also reduced the mean open time of the two largest conductance events of 38 and 43 pS; this reduction was voltage independent. Open‐time histograms were fitted with the sum of two exponentials. In the presence of 5 microM‐NMDA at ‐60 mV, tau o2 = 10.49 ms and tau o1 = 1.47 ms; in 30 microM‐zinc, tau o2 = 3.49 and tau o1 = 0.8 ms. The ‘blocking’ rate constant calculated at a membrane potential of +40 mV from the slope of 1/tau o2 vs. [zinc]o was 4 x 10(6) M‐1 S‐1. 4. Closed‐time analysis revealed brief (tau c = 0.4‐1.0 ms) zinc‐insensitive gaps; longer closed‐time intervals were not analysed since all patches contained more than one channel. Both burst duration and the number of bursts were reduced in the presence of zinc. 5. At holding potentials negative to ‐40 mV in magnesium‐free solutions, zinc also induced high‐frequency flickering of the open channel which included complete channel closures at 4 kHz filtering. No zinc‐induced flickering was seen at positive membrane potentials. The flickering was dose dependent, becoming prominent at zinc concentrations above 30 microM. Cadmium did not induce flickering at concentrations up to 100 microM.(ABSTRACT TRUNCATED AT 400 WORDS)
Carotid body chemoreceptor response to prolonged hypoxia in the rabbit: effects of domperidone and propranolol.
Authors: Li K Y , Ponte J , Sadler C L
Published: December 2014

1. The discharge of single afferent chemoreceptor fibres was recorded from the cut sinus nerve over periods of 60 or 90 min of constant, isocapnic hypoxia (arterial O2 pressure, Pa,O2, 3.13‐5.25 kPa), in twenty anaesthetized rabbits, after dividing the sympathetic supply to the carotid body. 2. Under control conditions, discharge after 60 min of hypoxia adapted to a mean (S.E.M.) of 71.95 (2.75)% of that attained at 5 min of hypoxia in twenty‐three hypoxic experiments. This adaptation was more pronounced when Pa,O2 was lower than 4 kPa (30 Torr). 3. Domperidone (1 mg kg‐1 bolus + 1 mg kg‐1 h‐1 infusion I.V.), increased normoxic afferent discharge by a mean of 142%. In ten experiments, discharge after 60 min of hypoxia adapted to a mean (S.E.M.) of 56.22 (+/‐ 3.40)% of that attained at 5 min of hypoxia which was significantly different from control hypoxic runs (P = 0.006). 4. In seven experiments propranolol (1 mg kg‐1 bolus + 1 mg kg‐1 h‐1 infusion I.V.) did not affect the normoxic discharge. The mean adaptation of discharge after 60 min of hypoxia was to 77.43 (3.97)% of discharge attained at 5 min of hypoxia, which was not significantly different from control hypoxic runs (P = 0.34). 5. Under control conditions plasma [K+] increased steadily during 60 min of hypoxia, in fourteen experiments, from a mean of 2.76 (0.14) to 2.85 (0.12) mmol l‐1 but this was not significant (P = 0.21). Domperidone (n = 6) did not affect plasma [K+] at any time, but after propranolol (n = 6) it increased by a mean (S.E.M.) of 0.39 (0.09) mmol l‐1 (P = 0.01) in normoxia and by a further 0.62 (0.28) mmol l‐1 (P = 0.08) at 60 min of hypoxia. 6. The results suggest that the adaptation of chemoreceptor discharge to hypoxia in the rabbit is not mediated by changes in plasma [K+]; in addition, endogenous dopamine, but not noradrenaline, contributes to the maintenance of chemoreceptor discharge in prolonged hypoxia.
A study of the developmental changes in outward currents of rat ventricular myocytes.
Authors: Kilborn M J , Fedida D
Published: December 2014

1. In ventricular muscle of rat heart, the action potential undergoes a major developmental change in shape in the days and weeks immediately after birth. Potassium (K+) currents which may affect the shape of the action potential have been studied using a whole‐cell voltage‐clamp technique with single cells from the ventricles of rats aged 1‐10 days. All recordings were made at 22‐23 degrees C. 2. Three discrete ages were chosen. 1‐day (cells isolated within 24 h of birth), 5‐day and 10‐day rats. These parallel the developmental action potential shortening from neonatal towards adult type. Action potentials of single myocytes were initially of long duration at 1 day with a prominent plateau phase, but had shortened somewhat by 10 days of age. The 5‐day group exhibited an action potential transitional in character between the earlier and later groups of cells. 3. Potassium current blocking agents were used to assess the importance of the various outward K+ currents for the action potential waveform at different ages. 4‐Aminopyridine (4‐AP; 2 x 10(‐3) M) which preferentially blocks voltage‐activated transient outward currents affected action potentials at all ages, but increases in duration were most pronounced in the 10‐day group. Only a small prolongation of the initial phase of repolarization of 1‐day action potentials was seen. Extracellular barium chloride, 0.1‐2 x 10(‐3) M, a blocker of inwardly rectifying potassium channels, had a marked slowing effect on repolarization in all the three age groups. Resting membrane depolarization was also produced by barium. 4. Developmental changes in the inwardly rectifying background current (IK1) and the cardiac transient outward current, It, were investigated. IK1 was recorded as the current sensitive to 2 x 10(‐3) M‐BaCl2 during voltage‐clamp steps from a holding potential of ‐90 mV. It was found to decrease in magnitude, approximately by a factor of three, from 15 to 5 pA/pF during the first ten postnatal days. This reduction can explain the maturational slowing of repolarization during the final phase of the action potential in rat heart. 5. Current‐voltage relations for IK1 from the three age groups crossed at the zero current potential at approximately ‐90 mV, near the calculated VK for the pipette filling solution and an external bath K+ concentration of 5 x 10(‐3) M. This suggests that IK1 channels in these cells are quite selective for K+ ions and that developmental changes in the potassium selectivity are not responsible for changes in IK1.(ABSTRACT TRUNCATED AT 400 WORDS)
The electrical response of cultured guinea‐pig coronary endothelial cells to endothelium‐dependent vasodilators.
Authors: Mehrke G , Daut J
Published: December 2014

1. Primary cultures of coronary endothelial cells were obtained by enzymatic dispersion of isolated guinea‐pig hearts and separation of different cardiac cell types by density gradient centrifugation. The cells were grown to confluency and the membrane potential of the monolayer was recorded using the whole‐cell‐clamp mode of the patch‐clamp technique. 2. When superfused with physiological salt solution at 37 degrees C the average resting potential of the monolayers was ‐35 +/‐ 9 mV. A 2 min application of bradykinin (0.1‐20 nM) induced a transient hyperpolarization of up to 40 mV (median 33 mV), which was followed by a sustained depolarization of up to 28 mV (median 10 mV). The average duration of the hyperpolarization, measured midway between the resting potential and peak negativity, was 48 s with 20 nM‐bradykinin. 3. The concentration of bradykinin producing a half‐maximal hyperpolarization was 2.5 nM. When high concentrations of bradykinin (greater than 10 nM) were applied for several minutes voltage oscillations of low amplitude with periodicity of 2‐3 min were observed. 4. The peak of the hyperpolarization depended on the extracellular potassium concentration ([K+]o). The limiting slope of the relation between membrane potential and log [K+]o was 52 mV per 10‐fold change in [K+]o. With 50 mM [K+]o the hyperpolarization was abolished and with 100 mM [K+]o the hyperpolarization turned into a depolarization. 5. After removal of external Ca2+ the first transient hyperpolarization elicited by bradykinin had the same amplitude as under control conditions, but its duration was reduced to about 72%. The second application of bradykinin in Ca2(+)‐free solution produced only a depolarization. The hyperpolarizing response to bradykinin could be re‐primed by exposing the preparation to Ca2(+)‐containing solution for 2 min. 6. The transient hyperpolarization elicited by 4 nM‐bradykinin could be inhibited by d‐tubocurarine, a blocker of Ca2(+)‐activated potassium channels. On average, 1 mM‐tubocurarine reduced the hyperpolarization by 49 +/‐ 18%. Apamin (10 microM) reduced the hyperpolarization by 15 +/‐ 11%. 7. ATP (1 microM) produced a hyperpolarization of similar amplitude to that produced by bradykinin, but of shorter duration (average 29 s), and a very small (less than 5 mV) or no sustained depolarization. Histamine (10 microM) produced an even shorter transient hyperpolarization, followed by a depolarization of up to 15 mV. 8. Most of the monolayers of coronary endothelial cells responded to adenosine in a similar way as to bradykinin.(ABSTRACT TRUNCATED AT 400 WORDS)
Multiple actions of pinacidil on adenosine triphosphate‐sensitive potassium channels in guinea‐pig ventricular myocytes.
Authors: Fan Z , Nakayama K , Hiraoka M
Published: December 2014

1. The patch‐clamp method was used to study the effects of pinacidil on the adenosine 5'‐triphosphate (ATP)‐sensitive K+ channel current in guinea‐pig ventricular myocytes. 2. In the inside‐out configuration of the patch membranes, the channel activity revealed a nearly fully open state in the absence of ATP, whereas application of ATP (0.1‐5 mM) markedly suppressed the channel opening. Addition of pinacidil (0.02‐1.0 mM) antagonized the inhibitory action of ATP and induced channel opening without marked change in conductance. An increase in ATP concentration depressed the maximal effect of pinacidil. Consequently, the dose‐response relationship of ATP inhibition was shifted to the right, but the shift approached a limiting value as pinacidil concentration was increased. The results indicate that the antagonism between pinacidil and ATP is not competitive. 3. The dose‐response curve for activation of the channel by pinacidil examined at ‐50 mV showed a sigmoidal shape but at +50 mV it had a convex shape, revealing asymmetry in the activating effects of pinacidil at these two voltages. 4. In the absence of ATP, pinacidil produced a voltage‐dependent block at positive voltages by decreasing the mean open time and increasing the mean closed time, whereas no such effects were observed at negative voltages. The concentration‐block relation at a given voltage was fitted to a first‐order Hill saturation function. The Kd (dissociation constant) decreased with depolarization from 2.2 mM at +20 mV to 0.15 mM at + 80 mV. 5. The kinetics of block and unblock by pinacidil were shown to be slow, and were expressed by a first‐order transition model. The blocking and unblocking rate constants were voltage dependent. 6. The slow block of single‐channel current showed an exponential decay in the ensemble current. The time constant of the decay was voltage dependent, reaching a maximal value at around +50 mV. 7. In the absence of ATP, the channel activity gradually decreased and eventually stopped within 12‐20 min, a process known as run‐down of channel activity. Calcium accelerated this run‐down process. Application of pinacidil partially reactivated the channel. Such channel reactivation by pinacidil during the course of run‐down depended upon the conditions of the patch and the time course of the run‐down. Pretreatment of the channel with ATP markedly strengthened the reactivation effect of pinacidil. 8. These results indicate that there are multiple sites or processes for interaction of pinacidil with the ATP‐sensitive K+ channel.
The in utero left ventricle of the fetal sheep: the effects of isoprenaline.
Authors: Anderson P A , Fair E C , Killam A P , Nassar R , Mainwaring R D , Rosemond R L , Whyte L M
Published: December 2014

1. Isoprenaline was infused into in utero fetal lambs to examine the effect of this beta‐adrenoceptor agonist on left ventricular stroke volume and left ventricular output and test the generally held assumption that the fetal ventricle is markedly limited in its ability to increase ventricular output. 2. Seven in utero lambs (121‐133 days of gestation) were instrumented with left ventricular dimension transducers, an ascending aortic electromagnetic flow transducer, a brachiocephalic arterial catheter and electrocardiographic and atrial pacing electrodes. 3. On the day of study, 5‐8 days following surgery and 129‐137 days of gestation, each lamb received infusions of isoprenaline, via the superior vena cava or left atrium, at rates which ranged from 0.005‐0.5 microgram kg‐1 min‐1. 4. Heart rate and left ventricular stroke volume, output and end‐diastolic and end‐systolic dimensions were measured under control conditions and during various levels of isoprenaline infusion, with and without controlling heart rate. 5. Analysis of variance was done using the mean cell model. Least‐square means and standard errors of the least‐square means are reported. F ratios were calculated from type III sums‐of‐squares; P less than 0.05 was considered significant. 6. The mean heart rate increased with isoprenaline (P less than 0.0001) from a mean control level of 169 +/‐ 8 to 281 +/‐ 9 beats min‐1 (+/‐ S.E.M.). 7. Mean left ventricular end‐diastolic and end‐systolic minor axis dimensions decreased significantly with isoprenaline from 16.7 +/‐ 0.1 mm (control) to 15.7 +/‐ 0.2 mm (P less than 0.0004) and from 11.7 +/‐ 0.1 mm (control) to 10.4 +/‐ 0.2 mm (P less than 0.0001) respectively. When heart rate was controlled with atrial pacing, mean end‐diastolic dimension increased significantly at the higher isoprenaline doses from 14.6 +/‐ 0.1 mm (control) to 15.3 +/‐ 0.2 mm (control) (P = 0.0002), while mean end‐systolic dimension fell significantly from 10.9 +/‐ 0.1 to 10.5 +/‐ 0.1 mm (P less than 0.003). Inasmuch as stroke volume increased, the increase in end‐diastolic dimension and the fall in end‐systolic dimension indicate an increase in venous return to the left ventricle. 8. During spontaneous rhythm, isoprenaline increased stroke volume from 2.45 +/‐ 0.06 ml (control) to 2.63 +/‐ 0.09 ml, not statistically significant. When heart rate was controlled, stroke volume increased with isoprenaline dose from 1.68 +/‐ 0.06 ml (control) to 2.40 +/‐ 0.08 ml (P less than 0.0001).(ABSTRACT TRUNCATED AT 400 WORDS)
Lateral diffusion of visual pigments in toad (Bufo marinus) rods and in catfish (Ictalurus punctatus) cones.
Authors: Gupta B D , Williams T P
Published: December 2014

1. The lateral diffusion coefficient, D, was determined for visual pigments in red rods, green rods and red‐sensitive cones with a photon‐counting microspectrophotometer. 2. A novel protocol that involved the placement on a photoreceptor of a single micromeasuring/bleaching beam permitted the determination of D of the pigment. 3. Demonstration that D for red rods compared very well with values obtained by other workers using other means validated the protocol. 4. Applied to green rods, the protocol gave a value of D that was about 80% greater than that for red rods. 5. D for cone pigment was found to be slightly less than that of red rod pigment. 6. The dichroic ratio of cones and the average orientation of the chromophore in the cone lamellae were 1.71 and 28.4 deg, respectively. 7. The photosensitivity at lambda max of the red‐sensitive cones was found to be about 16% less than that of red rods.