bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of P2‐purinoreceptors triggered Ca2+ release from InsP3‐sensitive internal stores in mammalian oligodendrocytes.
Authors: Kirischuk S , Scherer J , Kettenmann H , Verkhratsky A
Published: December 2014

1. The subcellular characteristics of an ATP‐induced elevation of the cytoplasmic free calcium concentration ([Ca2+]i) were studied in cultured cells of the oligodendrocyte lineage obtained from mouse cortex and rabbit retina, as well as in oligodendrocytes from mouse corpus callosum slices, using laser scanning confocal microfluorometry. 2. With the stage‐ and lineage‐specific antibodies O4 and O10, three developmental stages within the oligodendrocyte lineage were distinguished prior to Ca2+ recording. 3. Bath application of 1‐100 microM ATP induced a transient increase of [Ca2+]i in late precursors and oligodendrocytes but not in early glial precursor cells from retinal and cortical cultures and from corpus callosum slices. This effect of ATP was observed in Ca(2+)‐free extracellular solution, suggesting that the ATP‐mediated elevation of [Ca2+]i is due to a Ca2+ liberation from intracellular stores. 4. In both late precursors and oligodendrocytes from retina, the amplitude of ATP‐induced [Ca2+]i transients was significantly higher in processes as compared with the soma; in cortical cultures such an uneven response was only observed in oligodendrocytes, while in immature cells responses in soma and processes were of similar amplitude. 5. The rank order of potency for the purine and pyrimidine nucleotides was UTP > or = ATP > ADP >> AMP = adenosine = Me‐ATP for retinal oligodendrocytes, and ADP > or = ATP >> UTP = AMP = adenosine = Me‐ATP for cortical oligodendrocytes. The response to ATP and related nucleotides was blocked by suramin, indicating the involvement of a P2‐purinoreceptor in the ATP‐mediated [Ca2+]i response. 6. ATP‐induced elevation of the cytosolic Ca2+ concentration was inhibited by incubating cells with thapsigargin (10 microM) and by intracellular administration of heparin (1 microM). These findings indicate that ATP triggers a release of Ca2+ ions from InsP3‐sensitive internal stores. 7. The ATP receptors may play a role in neuron‐glial signal transfer; ATP is released as neurotransmitter, but also under pathological conditions from damaged cells.
Angiotensin II activation of a chloride current in rabbit cardiac myocytes.
Authors: Morita H , Kimura J , Endoh M
Published: December 2014

1. The effects of angiotensin II (Ang II) on membrane currents were investigated in single ventricular myocytes from the rabbit heart by the whole‐cell voltage‐clamp method. 2. In the presence of an inhibitor of Ca2+ currents (nifedipine at 3 microM or CdCl2 at 0.3 mM) and a beta‐adrenoceptor blocker (bupranolol at 1 microM), 1 microM Ang II significantly increased the membrane conductance. 3. After elimination of K+ from external and internal solutions and its replacement by Cs+, Ang II at 0.1 microM increased an outwardly rectifying current that reached a maximum after about 40 min. The effect was concentration dependent (10(‐9)‐10(‐6) M) and was inhibited by saralasin, an antagonist of Ang II receptors. 4. The reversal potential of the Ang II‐induced current in the absence of K+ was compatible with the Cl‐ equilibrium potential at various external concentrations of Cl‐. 5. A Cl‐ channel blocker, 4,4'‐dinitrostilbene‐2,2'‐disulphonic acid (DNDS, at 5 mM), reversibly decreased the Ang II‐induced current. 6. The Ang II‐induced current developed when the internal solution contained Ca2+ (pCa 7.2 or 7.0) but not when it contained 10 mM EGTA without Ca2+. 7. Besides developing a Cl‐ current, Ang II at 1 microM increased the inwardly rectifying K+ current (IK1) and this effect reached maximum within 3 min. 8. The effect of Ang II on the action potential was biphasic: the duration of the action potential was initially reduced and then it was increased. 9. These results suggest that Ang II induces a Cl‐ current that appears likely to modulate the action potential in rabbit ventricular myocytes.
Effects of testosterone on synaptic efficacy at neuromuscular junctions in a sexually dimorphic muscle of male frogs.
Authors: Nagaya N , Herrera A A
Published: December 2014

1. The effects of testosterone on synaptic efficacy were studied in the flexor carpi radialis, a sexually dimorphic forelimb muscle involved in frog clasping behaviour. Male Xenopus laevis frogs were castrated and then given either testosterone‐filled implants (CT frogs) or empty implants (C frogs) for 2, 8 or 16 weeks. 2. Intracellular recordings were made from fibres in the shoulder region and in a region midway between the elbow and wrist. These regions are mainly innervated by spinal nerve 2 (SN2) and spinal nerve 3 (SN3), respectively. 3. In CT muscles, the percentage of fibres that failed to generate an action potential in response to a single nerve stimulus was greater than in C muscles. The percentage of such fibres was greater among SN2 fibres than among SN3 fibres. 4. The input resistance and membrane time constant were lower in CT muscles than in C muscles for SN2 fibres but not for SN3 fibres. The action potential threshold was lower in CT muscles than in C muscles. In SN2 fibres, the action potential threshold was higher than in SN3 fibres. 5. Quantal content with 1 Hz nerve stimulation and miniature endplate potential (MEPP) frequency did not differ between CT and C junctions. However, both parameters were lower at SN2 junctions than at SN3 junctions. The amplitude of MEPPs was lower in CT muscles than in C muscles only for SN2 junctions. 6. Facilitation of transmitter release with 70 or 10 Hz nerve stimulation was greater at CT junctions than at C junctions. Also, SN2 junctions showed greater facilitation than SN3 junctions. 7. We hypothesize that the more androgen‐sensitive SN2 junctions, which have lower quantal content and greater facilitation, belong to motor units that are tonically active, fatigue resistant, and contract more slowly. The less androgen‐sensitive SN3 junctions, which have higher quantal content and less facilitation, may belong to motor units that are phasically active, fatigable and contract more rapidly. Testosterone enhances these differences such that flexor carpi radialis junctions are better adapted to the functional demands of clasping.
Spatial differences in fatigue‐associated electromyographic behaviour of the human first dorsal interosseus muscle.
Authors: Zijdewind I , Kernell D , Kukulka C G
Published: December 2014

1. Fatigue‐associated electromyographic (EMG) reactions of intrinsic hand muscles were studied during maintained isometric voluntary contractions of normal subjects. Most measurements concerned actions of the first dorsal interosseus (FDI). In a smaller number of subjects, complementary measurements were obtained for adductor pollicis (AP). 2. Measurements were made of isometric force (thumb adduction, index finger abduction and flexion) and of surface EMG amplitudes (AP and FDI) after rectification and smoothing (rsEMG). 3. In the analysis of fatigue, the subjects were required to maintain a steady isometric force (index finger abduction or thumb adduction) of half their maximum voluntary contraction (1/2MVC test) for as long as possible. Average endurance times were 88 +/‐ 19 s (mean +/‐ S.D.) for FDI and 119 +/‐ 29 s for AP (Student's t test, P < 0.02). 4. Pronounced differences in fatigue‐associated EMG behaviour were observed between AP and FDI. In AP the reaction was as expected: a rise of EMG during maintained force (mean rsEMG at end of fatigue test/mean rsEMG at start of test (rsEMG‐FI): 181 +/‐ 64%). In FDI this reaction was seen in half of the recorded cases, the remainder displaying bidirectional changes or a more or less marked decrease of EMG during the endurance task (mean for all cases together: rsEMG‐FI, 103 +/‐ 15%; difference between AP vs. FDI significant, P < 0.01). 5. The unexpected EMG variability of the FDI reactions was further analysed with multiple bipolar recordings of surface EMG. For all the four thoroughly studied subjects, recordings were obtained which showed simultaneously occurring EMG changes in opposite directions (decrease and increase) at different sites of FDI while force was kept constant at 50% of the maximum voluntary contraction (MVC). 6. Further observations on FDI showed that EMGs simultaneously obtained from different recording sites could show dramatic differences in their responses depending on ‘synergistic context’ (e.g. in relation to changes in index finger extension force during maintained abduction at 50% MVC). Evidence for ‘task switching’ (shift in rsEMG distribution, shift in hand muscle synergy) was frequently observed during the performance of the 1/2MVC test. 7. The results indicate that FDI is not handled in a topographically homogeneous manner during the execution of an isometric constant force endurance test. Furthermore, the results suggest that this seemingly simple motor performance can be executed in several alternative manners associated with the activation of different muscle synergies and with different distributions of activity within the FDI.
The delayed basolateral membrane hyperpolarization of the bovine retinal pigment epithelium: mechanism of generation.
Authors: Bialek S , Joseph D P , Miller S S
Published: December 2014

1. Conventional and ion‐selective double‐barrelled microelectrodes were used in an in vitro preparation of bovine retinal pigment epithelium (RPE)‐choroid to measure the changes in membrane voltage, resistance and intracellular Cl‐ activity (aCli) produced by small, physiological changes in extracellular potassium concentration ([K+]o). These apical [K+]o changes approximate those produced in the extracellular (subretinal) space between the photoreceptors and the RPE following transitions between light and dark. 2. Changing apical [K+]o from 5 to 2 mM in vitro elicited membrane voltage responses with three distinct phases. The first phase was generated by an apical membrane hyperpolarization, followed by a (delayed) basolateral membrane hyperpolarization (DBMH); the third phase was an apical membrane depolarization. The present experiments focus on the membrane and cellular mechanisms that generate phase 2 of the response, the DBMH. 3. The DBMH was abolished in the presence of apical bumetanide (100 microM); this response was completely restored after bumetanide removal. 4. Reducing apical [K+]o, adding apical bumetanide (500 mM), or removing apical Cl‐ decreased aCli by 25 +/‐ 6 (n = 8), 28 +/‐ 1 (n = 2) and 26 +/‐ 5 mM (n = 3), respectively; adding 100 microM apical bumetanide decreased aCli by 12 +/‐ 2 mM (n = 3). Adding apical bumetanide or removing apical bath Cl‐ hyperpolarized the basolateral membrane and decreased the apparent basolateral membrane conductance (GB). 5. DIDS (4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid) blocked the RPE basolateral membrane Cl‐ conductance and inhibited the DBMH and the basolateral membrane hyperpolarization produced by apical bumetanide addition or by removal of apical Cl‐o. The present results show that the DBMH is caused by delta[K]o‐induced inhibition of the apical membrane Na(+)‐K(+)‐2Cl‐ cotransporter; the subsequent decrease in aCli generated a hyperpolarization at the basolateral membrane Cl‐ channel.
Synaptic excitation of individual rat cerebellar granule cells in situ: evidence for the role of NMDA receptors.
Authors: D'Angelo E , De Filippi G , Rossi P , Taglietti V
Published: December 2014

1. Current‐clamp recordings were made in whole‐cell patch‐clamp configuration from ninety‐one granule cells in parasagittal cerebellar slices obtained from 21‐ to 31‐day‐old rats. Recordings were performed at 30 degrees C. 2. Resting membrane potential was ‐58 +/‐ 6 mV (n = 43). The membrane voltage response to step current injection showed inward rectification consistent with increasing input resistance during membrane depolarization. Over ‐35 +/‐ 7 mV (n = 14) repetitive firing with little or no adaptation was activated. Spike frequency increased nearly linearly with injected current. 3. Unitary EPSPs obtained by stimulating the mossy fibre bundle had an amplitude of 11.4 +/‐ 2.1 mV (n = 22, holding potential = ‐75 mV). Synchronous activation of greater than one to two mossy fibres was needed to elicit action potentials. Antidromic stimulation elicited antidromic spikes and also EPSPs, presumably through a mossy fibre ‘axon reflex’. 4. EPSPs were brought about by NMDA and non‐NMDA receptor activation, accounting for about 70 and 30%, respectively, of peak amplitude at the holding potential of ‐70 mV. The EPSP decay conformed to passive membrane discharge after blocking the NMDA receptors. 5. No appreciable correlation was found between the time‐to‐peak and decay time constant of the EPSPs, consistent with the compact electrotonic structure of these neurons. 6. During membrane depolarization EPSP amplitude increased transiently, due to both a voltage‐dependent increase of the NMDA component and inward rectification. In addition, EPSPs slowed down due to a slowdown of the NMDA component. 7. Temporal summation during high‐frequency stimulation was sustained by NMDA receptors, whose contribution to depolarization tended to prevail over that of non‐NMDA receptors during the trains. A block of the NMDA receptors resulted in reduced depolarization and output spike frequency. 8. This study, as well as extending previous knowledge to the intracellular level in vivo, provides evidence for a primary role of NMDA receptors in determining mossy fibre excitation of granule cells. It is suggested that the marked voltage dependence of the EPSP time course, which was mainly caused by voltage dependence in NMDA conductance, promotes the NMDA receptor‐dependent enhancement of granule cell coding observed during repetitive mossy fibre activity.
Functional effects of myoblast implantation into histoincompatible mice with or without immunosuppression.
Authors: Wernig A , Irintchev A , Lange G
Published: December 2014

1. The goals of this study were to evaluate the immunogenicity of myogenic cells (MCs) (1) immediately after implantation into regenerating muscles, and (2) following their maturation under initial immunosuppression. Implanted mouse soleus muscles were evaluated by isometric tension recordings in vitro followed by histological investigations on frozen sections. 2. Implantation of non‐histocompatible myoblasts into cryodamaged soleus muscles of CBA/J mice induced immune rejection which caused large and permanent deficits in muscle force: 4‐42 weeks postimplantation maximal tetanic tension was 50‐60% that of intact or regenerated cryodamaged control muscles without tendency for recovery or histological signs of muscle regeneration. Specific tension (force per unit muscle weight) was also significantly reduced. 3. On frozen sections, only 62 +/‐ 12% of the total area was desmin‐positive, that is, occupied by muscle fibres, versus 90 +/‐ 4% in regenerated and 92 +/‐ 3% in intact muscles. Also, the total number of muscle fibre profiles was significantly reduced. 4. Under immune suppression with cyclosporin A (CsA), large muscles developed within 4 weeks. Following CsA withdrawal, muscle weight and force, in addition to desmin‐positive areas on cross‐sections, gradually declined over several months despite continual regeneration, indicating retarded immune rejection. 5. Initial application of CsA for 8 weeks after implantation, instead of 4 weeks, did not result in better survival of the implants, nor did a higher initial dose of CsA (100 instead of 50 mg kg‐1 day‐1). Prolonged continuous application of a reduced dose (25 mg kg‐1 day‐1) did not prevent muscle wasting but caused an additional delay. 6. It is concluded that histoincompatible myoblasts are highly immunogenic and that immune rejection causes large and permanent muscle deficits indicating elimination of host muscle tissue. Initial transient immunosuppression protects the incompatible cells, but after withdrawal, prolonged immune rejection and retarded muscle wasting occur.
Role of fast inhibitory synaptic mechanisms in respiratory rhythm generation in the maturing mouse.
Authors: Paton J F , Richter D W
Published: December 2014

1. The importance of glycinergic and GABAAergic synaptic mechanisms for respiratory rhythm generation in the maturing mouse were investigated in vivo and in an in vitro slice preparation generating respiratory rhythmic activity spontaneously at all postnatal ages. 2. The effect on respiration of topical application of strychnine or bicuculline to the surface of the ventrolateral medulla was assessed in spontaneously breathing anaesthetized mice of different ages (postnatal (P) days 0 to > 56). Glycine receptor antagonization with concentrations of strychnine up to 25 microM was ineffective in altering the breathing pattern in neonates (P1‐P8). However, in mature mice (P > 15), low doses of strychnine (0.2‐2 microM) abolished regular rhythmic discharge in the phrenic nerve. Bicuculline (0.5‐50 microM) produced dose‐dependent increases in inspiratory time, amplitude and cycle length of phrenic nerve discharge in anaesthetized neonatal mice whereas both cycle length and duration of inspiratory activity were reduced in mature animals. In addition, in both neonates and mature mice low concentrations of bicuculline (0.5‐5 microM) abolished phrenic nerve discharge intermittently. 3. The response of respiratory‐modulated hypoglossal (XII) neurones recorded in tilted sagittal slices from newborn and mature mice during blockade of glycine and GABAA receptors was similar to the phrenic nerve changes observed in vivo: in slices from neonates, the rhythmic activity of XII neurones was resistant to concentrations of strychnine up to 50 microM whereas low doses of strychnine (0.2‐2 microM) abolished rhythmic activity in preparations from mature mice. Bicuculline (1‐50 microM) produced a dose‐dependent prolongation of burst duration and a slowing of rhythmic discharge in slices from neonatal mice whereas in mature mice rhythmic XII bursts were shortened and their frequency increased. At all maturational stages, bicuculline (1‐50 microM) induced severe disruption of the regular rhythm of XII neurone activity causing maintained depolarizations and oscillations in membrane potential. 4. On‐going inhibitory postsynaptic potentials of neurones located in the ventral respiratory group region of tilted sagittal slices from both immature and mature mice were sensitive to low concentrations of either bicuculline or strychnine (1‐5 microM) indicating an absence of a maturational change in the sensitivity of GABAA and glycine receptors to their respective antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)
Arachidonic acid activation of a new family of K+ channels in cultured rat neuronal cells.
Authors: Kim D , Sladek C D , Aguado-Velasco C , Mathiasen J R
Published: December 2014

1. The presence and properties of K+ channels activated by arachidonic acid were studied in neuronal cells cultured from the mesencephalic and hypothalamic areas of rat brain. 2. Arachidonic acid produced a concentration‐dependent (5‐50 microM) and reversible activation of whole‐cell currents. 3. In excised membrane patches, arachidonic acid applied to the cytoplasmic or extracellular side of the membrane caused opening of three types of channels whose current‐voltage relationships were slightly outwardly rectifying, inwardly rectifying and linear, and whose single channel slope conductances at +60 mV were 143, 45 and 52 pS, respectively. 4. All three currents were K+ selective and blocked by 2 mM Ba2+ but not by other K+ channel blockers such as tetraethylammonium chloride, 4‐aminopyridine and quinidine. The outwardly and inwardly rectifying currents were slightly voltage dependent with higher channel activity at more depolarized potentials. 5. Arachidonic acid activated the K+ channels in cells treated with cyclo‐oxygenase and lipoxygenase inhibitors (indomethacin and nordihydroguaiaretic acid), indicating that arachidonic acid itself can directly activate the channels. Alcohol and methyl ester derivatives of arachidonic acid failed to activate the K+ channels, indicating that the charged carboxyl group is important for activation. 6. Certain unsaturated fatty acids (linoleic, linolenic and docosahexaenoic acids), but not saturated fatty acids (myristic, palmitic, stearic acids), also reversibly activated all three types of K+ channel. 7. All three K+ channels were activated by pressure applied to the membrane (i.e. channels were stretch sensitive) with a half‐maximal pressure of approximately 18 mmHg. The K+ channels were not blocked by 100 microM GdCl3. 8. A decrease in intracellular pH (over the range 5.6‐7.2) caused a reversible, pH‐dependent increase in channel activity whether the channel was initially activated by arachidonic acid or stretch. 9. Glutamate, a neurotransmitter reported to generate arachidonic acid in striatal neurons, did not cause activation of the K+ channels when applied extracellularly in cell‐attached patches. 10. It is suggested that the K+ channels described here belong to a distinct family of ion channels that are activated by either fatty acids or membrane stretch. Although the physiological roles of these K+ channels are not yet known, they may be involved in cellular processes such as cell volume regulation and ischaemia‐induced elevation of K+ loss.
Changes in the effect of magnetic brain stimulation accompanying voluntary dynamic contraction in man.
Authors: Nielsen J , Petersen N
Published: December 2014

1. The soleus (Sol) H reflex was conditioned by magnetic stimulation of the contralateral motor cortex at rest and during voluntary contraction in healthy human subjects. The intensity of the magnetic stimulus was adjusted so as to have no effect on the H reflex at rest. During tonic voluntary contraction the same magnetic stimulus produced a facilitation with a short latency and a long duration, thus reflecting an increased excitation of Sol motoneurones by the magnetic stimulus during voluntary contraction. 2. The amount of reflex facilitation produced by brain stimulation within the initial 0.5‐1 ms after its onset was investigated at different times during dynamic ramp‐and‐hold plantar flexion. The facilitation was largest at the onset of voluntary activity in the Sol muscle. It then decreased abruptly within 100 ms after the onset of the voluntary contraction. Neither the voluntary Sol activity nor the control H reflex decreased at this time. 3. Electrical stimulation of the brain with the anode placed lateral to the vertex produced a facilitation of the H reflex, which preceded the facilitation evoked by magnetic stimulation by 1‐2 ms. The facilitation produced by the magnetic stimulus occurred or increased at the onset of contraction in relation to rest in all experiments. However, this was the case in only two out of eight experiments, when the brain was stimulated electrically. 4. The size of the reflex facilitation measured at the onset of contraction was larger the faster the contraction. Positive correlations were found between the size of the facilitation and the peak of the first and second derivative of the torque and the peak Sol EMG activity. 5. It is suggested that the observed changes in the size of the short‐latency reflex facilitation produced by magnetic brain stimulation mainly reflects changes in the excitability of corticospinal cells, since similar changes were not observed in the size of the unconditioned Sol H reflex or in the short‐latency reflex facilitation produced by electrical brain stimulation. The data support the hypothesis that fast conducting corticospinal fibres with monosynaptic projections to spinal motoneurones are involved in the initiation of voluntary movement in man.
Dendritic calcium transients evoked by single back‐propagating action potentials in rat neocortical pyramidal neurons.
Authors: Markram H , Helm P J , Sakmann B
Published: December 2014

1. Dendrites of rat neocortical layer V pyramidal neurons were loaded with the Ca2+ indicator dye Calcium Green‐1 (CG‐1) or fluo‐3, and the mechanisms which govern action potential (AP)‐evoked transient changes in dendritic cytosolic Ca2+ concentration ([Ca2+]i) were examined. APs were initiated either by synaptic stimulation or by depolarizing the soma or dendrite by current injection, and changes in fluorescence of the indicator dye were measured in the proximal 170 microns of the apical dendrite. 2. Simultaneous two‐pipette recordings of APs from the soma and apical dendrite, and dendritic fluorescence imaging indicated that a single AP propagating from the soma into the apical dendrite evokes a rapid transient increase in fluorescence indicating a transient increase in [Ca2+]i. At 35‐37 degrees C the decay time constant of the fluorescence transient following an AP was around 80 ms. 3. Voltage‐activated Ca2+ channels (VACCs) of several subtypes mediated the AP‐evoked fluorescence transient in the proximal (100‐170 microns) apical dendrite. The AP‐evoked fluorescence transient resulted from Ca2+ entry through L‐type (nifedipine sensitive; 25%), N‐type (omega‐conotoxin GVIA sensitive; 28%) and P‐type (omega‐agatoxin IVA sensitive; 10%) Ca2+ channels and through Ca2+ channels (R‐type) not sensitive to L‐, N‐ and P‐type Ca2+ channel blockers (cadmium ion sensitive; 37%). 4. The decay time course of the dendritic fluorescence transient was prolonged by the blockers of endoplasmic reticulum (ER) Ca(2+)‐ATPase, cyclopiazonic acid and thapsigargin, suggesting that uptake of Ca2+ into the ER in dendrites governs clearance of dendritic Ca2+. 5. The decay time course of the fluorescence transient was slightly prolonged by benzamil, a blocker of plasma membrane Na(+)‐Ca2+ exchange and by calmidazolium, a blocker of the calmodulin‐dependent plasma membrane Ca(2+)‐ATPase, suggesting that these pathways are less important for dendrite Ca2+ clearance following a single AP. Neither the mitochondrial uncoupler carbonyl cyanide p‐(trifluoromethoxy)phenylhydrazone (FCCP) nor the blocker of Ca2+ uptake into mitochondria, Ruthenium Red, had any measurable effect on the decay time course of the fluorescence transient. 6. Dendritic fluorescence transients measured during trains of dendritic APs began to summate at impulse frequencies of 5 APs s‐1. At higher frequencies APs caused a concerted and maintained elevation of dendritic fluorescence during the train.(ABSTRACT TRUNCATED AT 400 WORDS)
Calcium and sodium currents evoked by action potential waveforms in rat sympathetic neurones.
Authors: Toth P T , Miller R J
Published: December 2014

1. Calcium channel currents evoked by action potential waveforms were recorded from rat sympathetic neurones using the whole‐cell variant of the patch‐clamp technique. A voltage template was created in which the unmodified action potential (AP) was played back followed by a rectangular pulse. 2. The inhibitory effects of noradrenaline (NA) and neuropeptide Y (NPY) on the AP and rectangular pulse‐evoked currents, were compared. The percentage inhibition of the Ca2+ current produced by NA and NPY was significantly greater in the case of currents evoked using AP waveforms. 3. A train of APs was applied in the voltage command (40 or 75 Hz) and the inhibition produced by NPY on the AP‐evoked Ca2+ currents was examined. The inhibitory effect of NPY on the Ca2+ currents evoked by the high frequency APs did not change significantly during the train. 4. The AP falling phase was artificially prolonged and the resulting Ca2+ currents were compared. AP prolongation increased the amount of Ca2+ entering into the cell. However, the peak value of the Ca2+ current was primarily determined by the AP height. The AP plateau phase was also prolonged in defined voltage ranges. Prolongation in the positive voltage region was most effective in increasing the Ca2+ current. 5. Ion substitution studies were used to isolate Na+ and Ca2+ currents evoked by AP waveforms. The inhibitory effects of NA and oxotremorine (OXO‐M) on Ca2+ currents evoked by AP waveforms were examined in the presence and absence of the Na+ current.(ABSTRACT TRUNCATED AT 250 WORDS)
Contributions of human long‐wave and middle‐wave cones to motion detection.
Authors: Stromeyer C F , Kronauer R E , Ryu A , Chaparro A , Eskew R T
Published: December 2014

1. It has been suggested that motion may be best detected by the luminance mechanism. If this is the most sensitive mechanism, motion thresholds may be used to isolate the luminance mechanism and study its properties. 2. A moving (1 cycle deg‐1), vertical, heterochromatic (red‐plus‐green), foveal grating was presented on a bright yellow (577 nm wavelength) field. Detection and motion (direction identification: left versus right) thresholds were measured for different amplitude ratios of the red and green components spatially summed in phase or in antiphase. Threshold contours plotted in cone‐contrast co‐ordinates (L',M') for the long‐wave (L) and middle‐wave (M) cones, revealed two motion mechanisms: a luminance mechanism that responds to a weighted sum of L and M contrasts, and a spectrally opponent mechanism that responds to a weighted difference. 3. Detection and motion thresholds, measured at 1‐4 Hz, were identical for luminance gratings, having equal cone contrasts, L' and M', of the same sign. For chromatic gratings, with L' and M' of opposite sign, motion thresholds were higher than detection thresholds. A red‐green hue mechanism may mediate chromatic detection, and a separate spectrally opponent motion mechanism may mediate motion. 4. The red‐green hue mechanism was assessed from 1 to 15 Hz with an explicit hue criterion. The detection contour had a constant slope of one, implying equal L' and M' contributions of opposite sign. For motion identification, L' and M' contributed equally at 1 Hz, but the M' contribution was attenuated at higher velocities. 5. The cone‐contrast metric provides a physiologically relevant comparison of sensitivities of the two motion mechanisms. At 1 Hz, the spectrally opponent motion mechanism is approximately 4 times more sensitive than the luminance mechanism. As temporal frequency is increased, the relative sensitivities change so that the luminance mechanism is more sensitive above 9 Hz. 6. The less sensitive motion mechanism was isolated with a quadrature phase protocol, using a pair of heterochromatic red‐plus‐green gratings, counterphase flickering in spatial and temporal quadrature phase with respect to each other. One grating was set slightly suprathreshold and oriented in cone contrast (L',M') so as to potentiate a single motion mechanism, the sensitivity of which was probed with the second grating, which was varied in (L',M'). This allowed us to measure the motion detection contour of the less sensitive luminance mechanism at low velocities.(ABSTRACT TRUNCATED AT 400 WORDS)
Postnatal development of CO2‐O2 interaction in the rat carotid body in vitro.
Authors: Pepper D R , Landauer R C , Kumar P
Published: December 2014

1. The effect of PCO2 upon the discharge response to changes in PO2 (between ca 450 and 30 mmHg) was observed in adult (> 5 weeks old) and neonatal (5‐7 days old) rat carotid body chemoreceptors using an in vitro, superfused preparation. 2. In both adult and neonatal rats, regression analysis revealed that increasing PCO2 was without effect upon the shape of the PO2‐response curves (P > 0.30), but did cause an upward shift in the position of the curves, as indicated by a significant increase in the baseline chemoreceptor discharge during hyperoxia (0.22 +/‐ 0.02% maximum discharge per mmHg PCO2, P < 0.001, and 0.25 +/‐ 0.07% maximum discharge per mmHg PCO2, P < 0.005, respectively). However, whilst increasing PCO2 caused a significant rightward shift of the response curves in adults (0.75 +/‐ 0.23 mmHg PO2 per mmHg PCO2; P < 0.005), it was without effect in neonates (0.21 +/‐ 0.22 mmHg PO2 per mmHg PCO2; P > 0.200). Thus increasing levels of hypoxia increased CO2 chemosensitivity in adult but not in neonatal rats as shown by multiple regression analysis of the CO2‐response curves which revealed a significant interaction between PCO2 and PO2 for adult (P < 0.010) but not for neonatal (P > 0.150) rats. 3. We suggest that the previously reported maturation of peripheral chemoreceptor hypoxic sensitivity (resetting) may be due to the postnatal emergence of a significant degree of interaction between PCO2 and PO2 at the level of the peripheral chemoreceptor and/or its afferent innervation.
An ATP‐sensitive potassium conductance in rabbit arterial endothelial cells.
Authors: Katnik C , Adams D J
Published: December 2014

1. Whole‐cell patch clamp recording was used to study an ATP‐sensitive, sulphonylurea‐inhibitable potassium (K+) conductance in freshly dissociated endothelial cells from rabbit arteries. 2. The ATP‐sensitive K+ conductance was activated by micromolar concentrations of the K+ channel opener, levcromakalim, and by metabolic inhibition of endothelial cells using dinitrophenol and iodoacetic acid. The current‐voltage (I‐V) relationship obtained in isotonic K+ solutions was linear between ‐150 and ‐50 mV and had a slope conductance of approximately 1 nS. 3. The permeability of the ATP‐sensitive K+ conductance determined from reversal potential measurements exhibited the following ionic selectivity sequence: Rb+ > K+ > Cs+ >> Na+ > NH4+ > Li+. 4. Membrane currents activated by either levcromakalim or metabolic inhibition were inhibited by the sulphonylurea drugs, glibenclamide and tolbutamide, with half‐maximal inhibitory concentrations of 43 nM and 224 microM and Hill coefficients of 1.1 and 1.2, respectively. Levcromakalim‐induced currents were also inhibited by millimolar concentrations of Ba2+ or tetraethylammonium ions in the external solution. 5. Levcromakalim (3 microM) and metabolic inhibition hyperpolarized endothelial cells by approximately 10‐15 mV in normal physiological salt solutions. The hyperpolarization induced by levcromakalim or metabolic inhibition was inhibited by bath application of 10 microM glibenclamide. 6. Internal perfusion of the cytosol of whole‐cell voltage‐clamped endothelial cells with an ATP‐free pipette solution activated a membrane current which was reversibly inhibited by internal perfusion with a 3 mM MgATP pipette solution. This current was insensitive to other adenine and guanine nucleotides in the pipette solution. The inward current evoked in a nominally ATP‐free internal solution was further increased by bath application of levcromakalim. 7. Levcromakalim (25 microM) did not induce a change in the intracellular Ca2+ concentration of fura‐2‐loaded endothelial cells, whereas metabolic inhibition caused a slow and sustained increase in intracellular Ca2+ concentration, which was attenuated by 10 microM glibenclamide applied externally.(ABSTRACT TRUNCATED AT 400 WORDS)
Spontaneous, ligand‐independent activity of the cGMP‐gated ion channels in cone photoreceptors of fish.
Authors: Picones A , Korenbrot J I
Published: December 2014

1. We studied the electrical conductance of membrane patches detached from the outer segment of single cone photoreceptors isolated from striped bass retina. 2. Only a single class of ion channels exists in the plasma membrane of the cone outer segments; they are gated by cytoplasmic cGMP and select cations over anions, but distinguish poorly among cations. In the absence of added cGMP and of divalent cations, however, membrane patches detached from the outer segments exhibit a small conductance that ideally selects cations over anions, but distinguishes poorly between Na+ and Li+. 3. The cGMP‐independent conductance does not arise from the effect of residual cGMP that may remain associated with the detached membrane, because treatment of the patch with cGMP‐specific phosphodiesterase does not affect this conductance. 4. The cGMP‐independent conductance is pharmacologically indistinguishable from that activated by cGMP. Ca2+ and L‐cis‐diltiazem block both conductances at comparable concentrations and with similar quantitative characteristics. 5. We analysed the noise of Ca(2+)‐ or L‐cis‐diltiazem‐dependent macroscopic currents both in the presence and in the absence of cGMP. In the presence of cGMP, the power density spectrum of the noise is well fitted by the sum of two Lorentzian components. The same function with similar corner frequencies fits the noise of the cGMP‐independent currents. However, the total power in the current fluctuations is smaller in the absence of cGMP than in its presence; also, the ratio of the zero frequency asymptotes of the low over the high frequency components, S1(0)/Sh(0), is larger in the absence of cGMP than in its presence.(ABSTRACT TRUNCATED AT 250 WORDS)
Temporal structure in the light response of relay cells in the dorsal lateral geniculate nucleus of the cat.
Authors: Funke K , Wörgötter F
Published: December 2014

1. The spike interval pattern during the light responses of 155 on‐ and 81 off‐centre cells of the dorsal lateral geniculate nucleus (LGN) was studied in anaesthetized and paralysed cats by the use of a novel analysis. Temporally localized interval distributions were computed from a 100 ms time window, which was shifted along the time axis in 10 ms steps, resulting in a 90% overlap between two adjacent windows. For each step the interval distribution was computed inside the time window with 1 ms resolution, and plotted as a greyscale‐coded pixel line orthogonal to the time axis. For visual stimulation, light or dark spots of different size and contrast were presented with different background illumination levels. 2. Two characteristic interval patterns were observed during the sustained response component of the cells. Mainly on‐cells (77%) responded with multimodal interval distributions, resulting in elongated ‘bands’ in the 2‐dimensional time window plots. In similar situations, the interval distributions for most (71%) off‐cells were rather wide and featureless. In those cases where interval bands (i.e. multimodal interval distributions) were observed for off‐cells (14%), they were always much wider than for the on‐cells. This difference between the on‐ and off‐cell population was independent of the background illumination and the contrast of the stimulus. Y on‐cells also tended to produce wider interval bands than X on‐cells. 3. For most stimulation situations the first interval band was centred around 6‐9 ms, which has been called the fundamental interval; higher order bands are multiples thereof. The fundamental interval shifted towards larger sizes with decreasing stimulus contrast. Increasing stimulus size, on the other hand, resulted in a redistribution of the intervals into higher order bands, while at the same time the location of the fundamental interval remained largely unaffected. This was interpreted as an effect of the increasing surround inhibition at the geniculate level, by which individual retinal EPSPs were cancelled. A changing level of adaptation can result in a mixed shift/redistribution effect because of the changing stimulus contrast and changing level of tonic inhibition. 4. The occurrence of interval bands is not directly related to the shape of the autocorrelation function, which can be flat, weakly oscillatory or strongly oscillatory, regardless of the interval band pattern. 5. A simple computer model was devised to account for the observed cell behaviour. The model is highly robust against parameter variations.(ABSTRACT TRUNCATED AT 400 WORDS)
Mitochondrial membrane potential in single living adult rat cardiac myocytes exposed to anoxia or metabolic inhibition.
Authors: Di Lisa F , Blank P S , Colonna R , Gambassi G , Silverman H S , Stern M D , Hansford R G
Published: December 2014

1. The relation between mitochondrial membrane potential (delta psi m) and cell function was investigated in single adult rat cardiac myocytes during anoxia and reoxygenation. delta psi m was studied by loading myocytes with JC‐1 (5,5',6,6'‐tetrachloro‐1,1',3,3'‐ tetra‐ethylbenzimidazolylcarbocyanine iodide), a fluorescent probe characterized by two emission peaks (539 and 597 nm with excitation at 490 nm) corresponding to monomer and aggregate forms of the dye. 2. De‐energizing conditions applied to mitochondria, cell suspensions or single cells decreased the aggregate emission and increased the monomer emission. This latter result cannot be explained by changes of JC‐1 concentration in the aqueous mitochondrial matrix phase indicating that hydrophobic interaction of the probe with membranes has to be taken into account to explain JC‐1 fluorescence properties in isolated mitochondria or intact cells. 3. A different sensitivity of the two JC‐1 forms to delta psi m changes was shown in isolated mitochondria by the effects of ADP and FCCP and the calibration with K+ diffusion potentials. The monomer emission was responsive to values of delta psi m below 140 mV, which hardly modified the aggregate emission. Thus JC‐1 represents a unique double sensor which can provide semi‐quantitative information in both low and high potential ranges. 4. At the onset of glucose‐free anoxia the epifluorescence of individual myocytes studied in the single excitation (490 nm)‐double emission (530 and 590 nm) mode showed a gradual decline of the aggregate emission, which reached a plateau while electrically stimulated (0.2 Hz) contraction was still retained. The subsequent failure of contraction was followed by the rise of the emission at 530 nm, corresponding to the monomer form of the dye, concomitantly with the development of rigor contracture. 5. The onset of the rigor was preceded by the increase in intracellular Mg2+ concentration ([Mg2+]i) monitored by mag‐indo‐1 epifluorescence. Since under these experimental conditions intracellular [Ca2+] and pH are fairly stable, the increase in [Mg2+]i was likely to be produced by a decrease in ATP content. 6. The inhibition of mitochondrial ATPase induced by oligomycin during anoxia was associated with a rapid and simultaneous change of both the components of JC‐1 fluorescence, suggesting that delta psi m, instead of producing ATP, is generated by glycolytic ATP during anoxia. 7. The readmission of oxygen induced a rapid decrease of the monomer emission and a slower increase of the aggregate emission. These fluorescence changes were not necessarily associated with the recovery of mechanical function.(ABSTRACT TRUNCATED AT 400 WORDS)
H2O2‐induced chloride currents are indicative of an endogenous Na(+)‐Ca2+ exchange mechanism in Xenopus oocytes.
Authors: Schlief T , Heinemann S H
Published: December 2014

1. Defolliculated Xenopus oocytes were voltage clamped in bathing solutions containing 115 mM KCl and 1.8 mM CaCl2. External application of H2O2 transiently elicited voltage‐dependent outward rectifying currents within several seconds. Upon depolarization to +50 mV these currents had an activation time constant of 370 ms and reached amplitudes of up to 70 microA. This current was also observed in oocytes without the vitelline membrane. 2. The current was abolished by 500 microM niflumic acid, by the replacement of external Cl‐ by methanesulphonate, or when extracellular Ca2+ was removed indicating the involvement of Ca2+‐activated Cl‐ channels, which are very abundant in Xenopus oocytes. 3. While the current could be recorded in bathing solutions containing Li+, K+, Rb+, Cs+ and NH4+, extracellular Na+ abolished the current completely (IC50 = 6 mM Na+). 4. The H2O2‐induced Cl‐ current was half‐maximally blocked by approximately 25 microM 2'4'‐dichlorobenzamil, 250 microM MgCl2, 100 microM CdCl2 and 100 microM NiCl2. These substances have been shown to block Na+‐Ca2+ exchangers in various tissues. 5. The data are consistent with the existence of an endogenous Na+‐Ca2+ exchanger in the plasma membrane of Xenopus oocytes, which runs in reverse mode in the absence of high external Na+ and the presence of external Ca2+. This endogenous component has to be considered when Xenopus oocytes are used for heterologous expression studies.
Histamine and ATP mobilize calcium by activation of H1 and P2u receptors in human lens epithelial cells.
Authors: Riach R A , Duncan G , Williams M R , Webb S F
Published: December 2014

1. Cytoplasmic calcium concentration ([Ca2+]1) of single superfused tissue‐cultured human lens epithelial cells (HLEC) was monitored using the fluorescent dye fura‐2; the resting values were low and stable for several hours ([Ca2+]i = 96 +/‐ 20 nM; mean +/‐ S.D., n = 16). 2. Continuous superfusion with either ATP or histamine (0.1‐10 microM) produced regular oscillations in [Ca2+]i that could be maintained for a short time in the absence of external calcium. 3. Short (30 s) pulses of histamine (0.1‐100 microM) induced a transient rise in [Ca2+]i, the time course of which was insensitive to the removal of external calcium. The rate of rise and the amplitude of the response were very sensitive to agonist concentration, whereas the rate of recovery was relatively constant. 4. The responses to long pulses of histamine (> 100 s) consisted of an initial transient followed by a maintained [Ca2+]i which returned to baseline on removal of external calcium. 5. The kinetics of the responses to short and long pulses of ATP (0.1‐100 microM) were very similar to those of histamine and showed a similar sensitivity to the presence or absence of external calcium. 6. The histamine responses were abolished by triprolidine (1 microM), but unaffected by ranitidine (1 microM), indicating that an Hi receptor subtype is activated by histamine. 7. The ATP responses were reversibly inhibited by suramin and the potency sequence for a range of agonists was ATP = UTP = ATP gamma S > ADP = GTP >> AMP = adenosine, indicating that activation of a P2u receptor subtype was responsible for the increase in [Ca2+]i. 8. Both histamine and ATP responses were abolished by thapsigargin (100 nM), confirming that calcium release from intracellular stores was responsible for the initial peak of the response. Application of either agonist during the plateau phase of the thapsigargin response often led to a marked, but reversible, decline in [Ca2+]i, indicating the presence of a further, normally hidden, calcium regulatory factor associated with the presence of the agonist. 9. Maximal concentrations of either histamine or ATP totally emptied the calcium store as a subsequent application of the other agonist (or thapsigargin), in the absence of external calcium, failed to induce a further increase in the calcium signal.