bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuroeffector characteristics of sweat glands in the human hand activated by regular neural stimuli.
Authors: Kunimoto M , Kirnö K , Elam M , Wallin B G
Published: December 2014

1. Intraneural electrical stimuli (0.3‐1.2 mA, 0.2 ms) were delivered via a tungsten microelectrode inserted into a cutaneous fascicle in the median nerve at the wrist in twenty‐eight normal subjects. The effects on sweat glands within the innervation zone were monitored as changes of skin resistance and water vapour partial pressure (WVPP). Regional anaesthesia of the brachial plexus in the axilla eliminated spontaneous sympathetic activity and reflex effects. 2. At stimulation frequencies of 0.1 Hz each stimulus evoked a transient skin resistance reduction, the amplitude of which varied initially but reached a steady state of less than 10 k omega after, on average, nine responses. If preceded by stimulation‐free intervals of 5 min or more, up to fifteen stimuli were required before the first response occurred. With higher frequencies individual responses started to merge, skin resistance levels decreased successively and levelled off around 10 Hz. The total change of resistance (0‐10 Hz) was 101 +/‐ 46 (n = 9) k omega and the higher the pre‐stimulus level, the larger the reduction (r = 0.68, P less than 0.05). 3. Stimulus‐response latencies to the onset of a skin resistance reduction (single stimuli or trains of six impulses/20 Hz given at 0.1 Hz) shortened initially but reached steady‐state values after on average nine to twelve impulses. Average conduction velocity between stimulating electrode and skin resistance recording site was 0.78 m/s and average time for electrical neuroeffector transfer in sweat glands was estimated to be 348 ms. 4. In addition to direct stimulation‐induced resistance responses there were also small spontaneous reductions of resistance. They were seen in all subjects and at all frequencies but were more common in some subjects and occurred predominantly at the beginning of stimulation or at changes of frequency. They occurred independently at two skin sites in the same subject and disappeared during stimulation‐free periods and after atropine. 5. With train stimulation (six impulses/20 Hz) at 0.1 Hz, each train evoked transient increases of WVPP of 1 mmHg or less in some subjects (latency around 1.6 s). After averaging weak increases were seen also after single stimuli in two subjects. Increases of stimulation current or frequency led to slowly developing sustained increases of WVPP concomitant with decreases in skin resistance. 6. Responses in skin resistance and WVPP to train stimulation at 0.1 Hz were suppressed in a dose‐dependent way by I.V. injections of atropine.(ABSTRACT TRUNCATED AT 400 WORDS)
Rapid charge movements and photosensitivity of visual pigments in salamander rods and cones.
Authors: Makino C L , Taylor W R , Baylor D A
Published: December 2014

1. Photosensitivities of visual pigments were determined by measuring early receptor currents (ERCs) in voltage‐clamped photoreceptors from larval salamanders. 2. As expected from previous work of others, the ERC elicited by a brief flash consisted of a rapid inward component followed by a larger and slower outward component. The magnitude of the outward component corresponded to the movement of about 0.18 electronic charge across the membrane per photoisomerization. 3. The time course of the ERC was independent of the flash intensity, the flash wavelength and the magnitude of the response. The outward component of the cone ERC declined about twice as rapidly as the outward component of the rod ERC.. 4. The amplitude of the ERC decreased as successive flashes bleached the cell's pigment. Using the proportional relation between the size of the ERC and the number of pigment molecules photoisomerized, photosensitivities of the native A2 pigments in rods, red‐sensitive cones, blue‐sensitive cones and UV‐sensitive cones were determined. Calculated solution photosensitivities for rhodopsin, red‐sensitive and blue‐sensitive cone pigments were not significantly different and the average value for all three pigments at their respective absorption maxima was (7.3 +/‐ 1.6) x 10(‐9) micron 2 molecule‐1. A value of 44.0 x 10(‐9) micron 2 molecule‐1 was obtained in a single UV‐sensitive cone. 5. Substitution of the native dehydroretinal chromophore in the red‐sensitive cone pigment with 11‐cis‐retinal increased the solution photosensitivity to (9.6 +/‐ 0.62) x 10(‐9) micron 2 molecule‐1. 6. We conclude that cone pigments have large molecular absorption cross‐sections and high quantum efficiencies of photoisomerization. These properties seem well suited for the receptive molecules of a highly sensitive, miniaturized transducer.
Developmental changes in delayed rectifier K+ currents in the muscular‐ and neural‐type blastomere of ascidian embryos.
Authors: Shidara M , Okamura Y
Published: December 2014

1. Developmental changes in the amplitude, kinetic properties, tetraethyl‐ammonium (TEA) sensitivity, and ion selectivity of the delayed rectifier K+ currents were investigated in differentiating muscular‐type (M) and neural‐type (N) blastomeres isolated from the early cleavage‐arrested ascidian embryos, using conventional two‐microelectrode voltage clamp techniques. 2. No voltage‐sensitive outward K+ currents were found in either type of blastomere during the first 35 h of development at 9 degrees C. Thereafter the delayed rectifier K+ current became apparent. The peak amplitude of the K+ current in the M‐blastomere increased abruptly from 50 to 60 h and tended to plateau after 60 h, while in the N‐blastomere it continued to increase after initial emergence at around 35 h. 3. The threshold potential level of the K+ current in the M‐blastomere was initially about ‐10 mV in a standard external solution (1 mM‐K+ solution), but shifted towards the hyperpolarized direction until it reached a steady level at 45 h after fertilization. At the fully differentiated stages, the threshold was around ‐32 mV and ‐26 mV in the M‐ and N‐blastomeres, respectively. 4. Throughout development, the reversal potential of the tail current changed with the external K+ concentration in both M‐ and N‐blastomeres as expected for a K(+)‐electrode. There was no significant difference in the selectivity ratios for the K+ channel between the two types of blastomeres. The relative selectivities were K+ (1.000): Rb+ (0.774): NH4+ (0.122): Na+ (0.074) and K+ (1.000): Rb+ (0.724): NH4+ (0.155): Na+ (0.074) in the M‐ and N‐blastomeres, respectively. 5. Modified Scatchard plots of TEA‐sensitivity data indicated a one‐to‐one reaction between TEA and the K+ channel. These plots revealed the presence of TEA‐resistant K+ channels in addition to TEA‐sensitive K+ channels in the M‐blastomere, but revealed only TEA‐sensitive K+ channels in the N‐blastomere. The dissociation constant (Ki) values of these three types of K+ channel did not change during development. In the M‐blastomere, the Ki of the TEA‐sensitive K+ channel was 1.29 +/‐ 0.05 mM (mean +/‐ S.E.M., n = 31) and that of the TEA‐resistant K+ channel was 1.4 +/‐ 0.1 M (mean +/‐ S.E.M., n = 31) at a test potential of 45 mV. The Ki value of the neural‐type K+ current was 1.38 +/‐ 0.03 mM (mean +/‐ S.E.M., n = 20) at 45 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
Asymmetries of oxygen uptake transients at the on‐ and offset of heavy exercise in humans.
Authors: Paterson D H , Whipp B J
Published: December 2014

1. At work rates which do not result in a sustained increase in blood lactate ([L‐]), oxygen uptake (VO2) approaches the steady state with first‐order kinetics. However, when [L‐] is increased, at least two kinetic components are required to characterize the VO2 response dynamics. The purpose of the present investigation was to determine whether these more‐complex kinetics are best represented as: (a) two components which operate throughout the exercise or (b) a delayed slow component which is consequent to the lactic acidaemia and which does not influence the early development of the O2 deficit. 2. Six healthy subjects underwent an incremental ramp test on a cycle ergometer, to the limit of tolerance, for determination of the maximum VO2 (micro VO2) and and estimation [symbol: see text] of the threshold for lactic acidaemia (theta L) non‐invasively. Subjects then performed, on different days, two to four repetitions of square‐wave exercise from a baseline of unloaded pedalling ('O' Watts (W)) to work rates (WR) less than theta L (90% theta L) and greater than theta L (half‐way between theta L and micro VO2). Ventilatory and pulmonary gas exchange variables were determined breath‐by‐breath. For each subject, the VO2 transitions were averaged prior to fitting a least‐squares algorithm to the on‐ and off‐transient responses. 3. The less than theta L test resulted in a mono‐exponential VO2 response, with a time constant of 31.3 and 31.5 s for the on‐ and off‐transients, respectively. 4. The VO2 responses to the greater than theta L test were fitted to three competing models: (a) a single exponential for the entire period; (b) a double exponential for the entire period; and (c) an initial single exponential with a subsequent phase of delayed onset. Model (c) yielded a significantly lower residual mean‐squares error than methods (a) and (b), with a time constant for the initial component of 40.2 s for the on‐transient and 32.9 s for the off‐transient and a subsequent phase of VO2 increase for the on‐transient which averaged 230 ml min‐1. The delta VO2/delta WR for the early kinetics of the greater than theta L test were not different from the less than theta L test (9.6 and 9.5 ml min‐1 W‐1, respectively). 5. These data suggest that the slow phase of the greater than theta L VO2 kinetics is a delayed‐onset process. This being the case, the O2 deficit during heavy exercise, as conventionally estimated, would be overestimated.
Tetanic stimuli induce a short‐term enhancement of recurrent inhibition in the CA3 region of guinea‐pig hippocampus in vitro.
Authors: Miles R
Published: December 2014

1. Recordings were made from pre‐ and postsynaptic cells at synapses involved in generating synaptic inhibition in the CA3 region of slices from guinea‐pig hippocampus to examine the short‐term effects of tetanic stimuli on recurrent inhibitory circuits. 2. Disynaptic inhibitory interactions were facilitated for a period of 2‐5 min after tetanic stimulation of afferent fibres. The facilitation was due to an increase in the probability that IPSPs were transmitted. The amplitude of IPSPs that were evoked did not change. 3. IPSPs elicited by single action potentials in inhibitory cells were not changed immediately after tetanic stimulation. 4. There was no short‐term change in the amplitude of unitary or spontaneously occurring EPSPs recorded from inhibitory cells. 5. The frequency of spontaneous IPSPs recorded in CA3 pyramidal cells increased transiently after tetanic stimuli delivered in the presence of excitatory amino acid receptor antagonists. 6. Tetanic stimuli caused a voltage‐dependent increase in excitability of CA3 inhibitory cells. Little effect was apparent at hyperpolarized potentials. Near resting potential, tetanic stimuli enhanced inhibitory cells firing frequency partly by increasing the rate of membrane repolarization after an action potential. 7. These findings suggest tetanic stimulation releases a transmitter or other factor that alters intrinsic currents of CA3 inhibitory cells for several minutes, increasing their excitability and resulting in a transient facilitation of recurrent synaptic inhibition.
Extracellular MgATP activates the Cl‐/HCO3‐ exchanger in single rat cardiac cells.
Authors: Pucéat M , Clément O , Vassort G
Published: December 2014

1. The effect of extracellular MgATP on cytosolic pH (pHi) was investigated in single rat cardiac cells loaded with the pH‐sensitive probe Snarf‐1. 2. Basal pHi in HEPES‐buffered solution (containing 4.4 mM‐NaHCO3) was 7.08. MgATP induced a transient acidification followed by an alkalinization. The latter is prevented by ethylisopropylamiloride (EIPA) and has been attributed to the activation of the Na+/H+ antiport. The MgATP‐induced acidification reached a maximal value of 0.42 +/‐ 0.03 pH units (U pH). It was concentration dependent with a K0.5 of 2.6 microM‐MgATP. This acidification was also observed with the same magnitude in the presence of the more physiological Krebs‐bicarbonate buffer but was greatly reduced in nominally HCO3‐free HEPES. 3. The MgATP‐induced acidification was prevented by 4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid (DIDS), probenecid and ethacrynic acid but not by bumetanide. It was dependent upon the external chloride concentration. The K0.5[Cl‐] was 9 mM and the maximal acidification required 60 mM‐Cl‐. 4. MgATP accelerated the recovery from an alkalinization triggered by a pulse of NH4Cl. The nucleotide also facilitated the efflux of HCO3‐ when the cell was switched from a Krebs‐bicarbonate buffer gassed with 5% CO2 to an HEPES buffer. 5. The acidification was only evoked by MgATP and its poorly hydrolysable analogues but not by the other nucleotides (ADP, GTP (guanosine triphosphate), CTP (cytidine triphosphate) UTP (urodine triphosphate), ITP (inositol triphosphate) nor by adenosine. It required the presence of Mg2+ ions. 6. These results provide evidence that MgATP activates the Cl‐/HCO3‐ exchanger and that this activation accounts for the acidification. Such an activation could not be related to the P1‐ or the P2‐purinergic receptors since it requires triphosphate adenylic compounds and Mg2+ ions. This leads us to suggest the existence of a putative P3‐type of purinergic receptor.
Increases in intracellular calcium ion concentration during depolarization of cultured embryonic Xenopus spinal neurones.
Authors: Barish M E
Published: December 2014

1. Changes in intracellular Ca2+ ion concentrations ([Ca2+]i) during potassium‐induced depolarizations were studied in cultured embryonic Xenopus spinal neurones using the Ca(2+)‐sensitive dye Fura‐2 and quantitative fluorescence microscopy. 2. Membrane voltages attained during exposure to bath solutions containing 3, 10, 20, 30, 40 and 50 mM‐K+ were determined under current clamp. In 3 mM‐K(+)‐containing solution (normal saline), the resting potential was ‐65 mV. The threshold voltage required to observe a measurable rise in [Ca2+]i was ‐40 mV (external potassium concentration [K+]o = 20 mM). The depolarization‐induced [Ca2+]i signal had two components: a non‐relaxing component, and, at voltages positive to ‐40 mV, an additional transient component on the rising phase that decayed over tens of seconds. There was substantial variability in the magnitudes of resting and voltage‐induced changes in [Ca2+]i, but [Ca2+]i responses were qualitatively consistent between neurons of similar ages. 3. External potassium (K+o)‐induced increases in [Ca2+]i were spatially non‐homogeneous. The largest increases were seen in the nucleus, near the base of a major neurite, and in growth cones. Increases occurred more rapidly in neurites and growth cones than in somas. T‐type and high‐voltage‐activated (HVA) channels appeared to be present in all cell regions. 4. Increases in [Ca2+]i evoked by 50 mM‐K+ (depolarization to approximately ‐15 mV) were sensitive to treatments demonstrated to inhibit Ca2+ currents in these cells (T‐type, HVA‐relaxing and HVA‐sustained), including Ni2+ (200 microM), Metenkephalin (17.5 microM), and omega‐conotoxin (omega‐CgTx; 5.5 microM). [Ca2+]i increases were reduced by caffeine (10 mM) and ryanodine (10‐100 microM), agents that affect Ca2+ release from intracellular stores. 5. A sustained increase in [Ca2+]i observed at approximately ‐40 mV ([K+]o = 20 mM) was investigated in greater detail. Concentrations of Ni2+ sufficient to block T‐type Ca2+ current slowed but did not block the rise in [Ca2+]i induced by 20 mM‐K+. Met‐enkephalin did not affect the [Ca2+]i response. omega‐CgTx reduced the amplitude of the [Ca2+]i response, but did not eliminate the sustained component. Verapamil (100 microM), caffeine and ryanodine differentially reduced the sustained component as compared to the initial rising phase. These observations suggest that the rising phase was due to Ca2+ influx through T‐type and other Ca2+ channels, and that the sustained phase was differentially sensitive to inhibition of internal Ca2+ release.(ABSTRACT TRUNCATED AT 400 WORDS)
Two types of high‐threshold calcium currents inhibited by omega‐conotoxin in nerve terminals of rat neurohypophysis.
Authors: Wang X , Treistman S N , Lemos J R
Published: December 2014

1. The neurohypophysis comprises the nerve terminals of hypothalamic neurosecretory cells, which contain arginine vasopressin (AVP) and oxytocin. The secretory terminals of rat neurohypophyses were acutely dissociated. The macroscopic calcium currents (ICa) of these isolated peptidergic terminals were studied using ‘whole‐cell’ patch‐clamp recording techniques. 2. There are two types (‘Nt’ (where the subscript ‘t’ denotes terminal) and ‘L’) of high‐threshold voltage‐activated ICa in the terminals, which can be distinguished by holding at different potentials i.e. ‐90 and ‐50 mV. Replacement of Ca2+ in the bathing solution by Ba2+ increased the amplitude of ICa, primarily due to an increase in the L‐type component. Both inward currents were eliminated by adding 50 microM‐Cd2+ or when in a Ca(2+)‐free bathing solution. 3. omega‐Conotoxin GVIA (omega‐CgTx) has been widely used as a Ca2+ channel blocker. However, whether this toxin can discriminate between different types of Ca2+ channels is still a subject of controversy. We applied omega‐CgTx over a wide range of concentrations (0.01‐2 microM) to examine its effects on both Nt‐ and L‐type ICa in these terminals. At a concentration of 30 nM, omega‐CgTx selectively reduced, by 48%, the amplitude of Nt‐type ICa. In contrast, a higher concentration (300 nM) of omega‐CgTx was necessary to inhibit the L‐type ICa. 4. omega‐CgTx inhibited both Nt‐ and L‐type ICa in a dose‐dependent manner, and the half‐maximum inhibition (IC50) of the ICa by the toxin was 50 and 513 nM, respectively, which was approximately a tenfold difference. The reduction in both types of currents did not result from any shift in their current‐voltage or steady‐state inactivation relationships. 5. In contrast, omega‐CgTx, at a concentration of 300 nM, had no effect on the tetrodotoxin‐sensitive sodium current (INa) of the isolated peptidergic nerve terminals. Furthermore, omega‐CgTx did not reduce the long‐lasting, non‐inactivating ICa in the isolated non‐neuronal secretory cells of the pars intermedia (PI) (intermediate lobe of the pituitary). 6. Our studies suggest that omega‐CgTx might exert specific blocking effects on both Nt‐ and L‐type Ca2+ channels, but that in the isolated peptidergic nerve terminals, the Nt‐type component is more susceptible to this toxin.
Changes in R‐R interval at the start of muscle contraction in the decerebrate cat.
Authors: McMahon S E , McWilliam P N
Published: December 2014

1. The effect on R‐R interval of a brief hindlimb contraction, elicited by electrical stimulation of L7 ventral roots, was investigated in decerebrate cats. The first series of experiments was performed at both low and high carotid sinus pressure to vary the level of vagal tone. When carotid sinus pressure was elevated to increase vagal tone, contraction commenced 1 s later. 2. The change in R‐R interval at low carotid sinus pressure was expressed as the difference between the mean of the five R‐R intervals immediately preceding contraction and the mean of the last five R‐R intervals at the end of a 5 s contraction. At high carotid sinus pressure, the change was expressed as the difference between the mean of the last five R‐R intervals at the end of a 5 s contraction and the mean of five R‐R intervals at an equivalent time after raising pressure alone. 3. Hindlimb contraction at low carotid sinus pressure produced a significant reduction in R‐R interval from 359 +/‐ 25 (mean +/‐ S.E.M. n = 8) to 336 +/‐ 24 ms (P less than 0.005). At high carotid sinus pressure the response was enhanced with contraction producing a reduction in R‐R interval from 474 +/‐ 45 to 419 +/‐ 47 ms (P less than 0.001). 4. The shortening of R‐R interval produced by hindlimb contraction at high carotid sinus pressure, 55 +/‐ 8 ms, was significantly greater than that observed at low sinus pressure, 23 +/‐ 5 ms (P less than 0.001, n = 8, paired t test). This pattern of response was also seen at stimulation frequencies as low as 10 Hz. 5. In a second series of experiments, designed to determine the latency of the cardiac acceleration, the minimum latency between the onset of L7 ventral root stimulation and the end of the first shortened R‐R interval was 687 +/‐ 29 ms (n = 5). 6. Atropine (0.4 mg kg‐1, I.V.) prevented a 5 s contraction from producing any change in R‐R interval. 7. These results indicate that afferent information originating from receptors in contracting muscles is responsible for producing an immediate shortening of R‐R interval, which is mediated by vagal withdrawal. The possibility that the shortening of R‐R interval at the start of contraction is linked to a reduction in arterial baroreceptor reflex sensitivity, possibly via inhibitory effects on neurones forming the central pathway of the baroreceptor reflex, is discussed.
ATP‐sensitive K+ channels and cellular K+ loss in hypoxic and ischaemic mammalian ventricle.
Authors: Weiss J N , Venkatesh N , Lamp S T
Published: December 2014

1. The contribution of ATP‐sensitive K+ (K+ATP) channels to the rapid increase in cellular K+ efflux and shortening of action potential duration (APD) during early myocardial ischaemia and hypoxia remains controversial, because for the first 10 min of ischaemia or hypoxia in intact hearts cytosolic [ATP] remains about two orders of magnitude greater than the [ATP] causing half‐maximal blockade of K+ATP channels in excised membrane patches. The purpose of this study was to investigate this apparent discrepancy. 2. During substrate‐free hypoxia, total, diastolic and systolic unidirectional K+ efflux rates increased by 43, 26 and 103% respectively after 8.3 min in isolated arterially perfused rabbit interventricular septa loaded with 42K+. APD shortened by 39%. From the Goldman‐Hodgkin‐Katz equation, the relative increases in systolic and diastolic K+ efflux rates were consistent with activation of a voltage‐independent K+ conductance. 3. During total global ischaemia, [K+]o measured with intramyocardial valinomycin K(+)‐sensitive electrodes increased at a maximal rate of 0.68 mM min‐1, which could be explained by a less than 26% increase in unidirectional K+ efflux rate (assuming no change in K+ influx), less than the increase during hypoxia. APD shortened by 23% over 10 min. 4. During hypoxia and ischaemia, cytosolic [ATP] decreased by about one‐third from 6.8 +/‐ 0.5 to 4.3 +/‐ 0.3 and 4.6 +/‐ 0.4 mM respectively, and free cytosolic [ADP] increased from 15 to 95 and approximately 63 microM respectively. 5. To estimate the percentage of activation of current through K+ATP channels (IK,ATP) necessary to double the systolic K+ efflux rate (comparable to the increase during hypoxia), K+ efflux during a single simulated action potential was measured by blocking non‐K+ currents under control conditions and after IK,ATP was fully activated by metabolic inhibitors. Activation of 0.41 +/‐ 0.07% of maximal IK,ATP was sufficient to double the systolic K+ efflux rate. The equivalent amount of constant hyperpolarizing current also shortened the APD in the isolated myocytes by 41 +/‐ 5%, compared to the 39% APD shortening observed during hypoxia in the intact heart. 6. The degree of activation of IK,ATP expected to occur during hypoxia and ischaemia was estimated by characterizing the ATP sensitivity of K+ATP channels in the presence of 2 mM‐free Mgi2+ and 0, 10, 100 and 300 microM‐ADPi in inside‐out membrane patches excised from guinea‐pig ventricular myocytes.(ABSTRACT TRUNCATED AT 400 WORDS)
Corticospinal projections to upper limb motoneurones in humans.
Authors: Palmer E , Ashby P
Published: December 2014

1. Magnetic stimulation was applied over the motor cortex in forty‐five normal human subjects and peristimulus time histograms (PSTHs) of the discharges of single motor units were used to record changes in the firing probability of individual spinal motoneurones of contralateral upper limb muscles. Recordings were obtained from 153 motor units from fourteen upper limb muscles. 2. For the majority of motor units the initial effect was a short latency facilitation. The estimated central conduction velocities and the rise times of the underlying excitatory postsynaptic potentials (EPSPs) were compatible with monosynaptic facilitation by a fast corticospinal pathway. In some motor units the initial effect was a short latency inhibition. Other units showed no statistically significant changes in firing probability. The proportion of the tested motor units in each of these categories depended on the muscle. All of the sampled units of first dorsal interosseous (1DI) showed short latency facilitation, as did the majority of units in the forearm and the biceps brachii. More than half of the sampled motor units of triceps brachii and deltoid showed either no effect or were inhibited. 3. To compare the net short latency actions of the neurones activated by magnetic stimulation on various motoneurone pools, the magnitude of the short latency facilitation or inhibition in a given motor unit was normalized to the magnitude of the short latency facilitation in the 1DI motor unit of the same subject at the same stimulus intensity, and these data were pooled for a number of subjects. 4. 1DI motoneurones received strong net facilitation (estimated mean EPSP amplitude 2.9 +/‐ 0.2 mV), the motoneurones of forearm muscles and biceps brachii received weaker net facilitation and triceps brachii and deltoid received no net effect. 5. It is concluded that the short latency corticospinal projections to upper limb motoneurones in humans have a distinct pattern which is similar to that in other primates.
Confocal microscopic imaging of [Ca2+]i in cultured rat hippocampal neurons following exposure to N‐methyl‐D‐aspartate.
Authors: Segal M , Manor D
Published: December 2014

1. The confocal laser scanning microscope (CLSM) was used in conjunction with the calcium indicator dye Fluo‐3 to record changes in free intracellular calcium concentration ([Ca2+]i) in cultured hippocampal neurons in response to superfusion of N‐methyl‐D‐aspartate (NMDA). 2. NMDA caused a rapid rise in [Ca2+]i in all parts of the neuron. The rise in [Ca2+]i was dependent on activation of an NMDA receptor, was enhanced by the removal of Mg2+ and addition of glycine to the superfusion medium, and was dependent on normal [Ca2+]o. 3. The rise of [Ca2+]i was seen first near the membrane. A wave of elevated [Ca2+]i moved centripetally at a rate of 117 microns/s. 4. Dantrolene pre‐incubation caused a significant reduction in the efficacy of the NMDA‐induced rise in [Ca2+]i, indicating that at least part of the rise is caused by intracellular release of calcium. 5. The replacement of calcium by barium caused a reduction in the response to NMDA, but a significant response was still present in these cells, supporting the assumption that NMDA causes release of calcium from intracellular stores. 6. The removal of sodium from the superfusion medium prolonged the [Ca2+]i rise in response to NMDA indicating that the Na‐Ca antiporter is instrumental in reducing [Ca2+]i. 7. These studies demonstrate the multiplicity of regulating mechanisms of [Ca2+]i following activation of NMDA receptors.
Enhancement of gamma‐aminobutyric acid‐activated Cl‐ currents in cultured rat hippocampal neurones by three volatile anaesthetics.
Authors: Jones M V , Brooks P A , Harrison N L
Published: December 2014

1. The effects of the volatile anaesthetics enflurane, halothane and isoflurane on gamma‐aminobutyric acid (GABA)A receptor‐mediated chloride currents were studied in cultured rat hippocampal neurones. Transient current responses were obtained by brief pressure application of GABA to the cell body of neurones under voltage clamp. 2. All three anaesthetics increased the peak amplitude and duration of current 2. All three anaesthetics increased the peak amplitude and duration of current responses to brief applications of GABA. These effects were fully reversible, and did not involve alterations in the reversal potential for GABA responses. 3. The experimental concentrations of anaesthetics were measured directly using gas chromatography. The enhancement of GABA currents increased with increasing anaesthetic concentration. Clinically effective concentrations of anaesthetics (between 1 and 1.5 times MAC (minimum alveolar concentration) produced significant enhancement of GABA currents. 4. These results demonstrate that the changes in the time course of synaptic inhibition reported in the presence of the volatile anaesthetics are likely to result from modification of the function of postsynaptic GABAA receptor‐channel complexes. These findings also support the hypothesis that GABAA receptor complexes serve as common molecular target sites for a variety of structurally diverse anaesthetic molecules.
Longitudinal chromatic aberration and emmetropization: results from the chicken eye.
Authors: Rohrer B , Schaeffel F , Zrenner E
Published: December 2014

1. Due to the chromatic dispersion of the ocular media, the focal length of the optics of the eye is about 3 diopters longer for red light than for blue light. Because emmetropization in the chicken (Gallus domesticus) does not require colour cues and operates properly in monochromatic light, one can, therefore, expect that chickens raised in red light become more myopic (with longer eyes) than chicks raised in short wavelength light. Prior to conducting this experiment, we matched the brightness of both light conditions by means of flicker electroretinograms such that equiluminance was obtained for the chickens. 2. Unexpectedly, refractive development was not different from controls in white light for either red or near‐ultraviolet light. 3. We tested whether the visual mechanisms guiding refractive development were still sensitive to defocus under both illuminations by treating the chicks with spectacle lenses. 4. Similar to a previous experiment in white light, the growth of the eye in red light also changed such that it compensated for the imposed defocus. It failed to do so, however, in near‐ultraviolet light. 5. A histological analysis of the sampling intervals for the ultraviolet receptor system revealed that its spatial resolving power was too low to detect the defocus imposed by the lenses, whereas the long wavelength receptors provided sufficiently good visual acuity. 6. The results show that, during emmetropization, the chicken eye elegantly bypasses the problem of multiple chromatic focal planes by having a low sensitivity to defocus in the blue end of the spectrum. Because the chromatic dispersion function is steep in the blue range but flat at the red end of the spectrum, the remaining chromatic defocus in the spectral range of high visual acuity is low and may match the depth of field of the eye.
Protein kinase C‐mediated enhancement of NMDA currents by metabotropic glutamate receptors in Xenopus oocytes.
Authors: Kelso S R , Nelson T E , Leonard J P
Published: December 2014

1. N‐Methyl‐D‐aspartate (NMDA) receptors were expressed in Xenopus oocytes injected with rat brain RNA. The modulation of NMDA‐induced currents was examined by activating protein kinase C (PKC) either directly (using phorbol esters) or indirectly (via metabotropic glutamate agonists). 2. Bath application of the PKC activator, 4‐beta‐phorbol‐12,13‐dibutyrate (PDBu) resulted in a two‐fold increase in the NMDA‐evoked current at all holding potentials examined (‐80 to 0 mV). The inactive (alpha) stereoisomer of phorbol ester was ineffective. 3. The increase was observed under conditions that eliminate the oocyte's endogenous calcium‐dependent chloride current, which often contributes to the NMDA response in oocytes. 4. The PDBu effect was specific to the NMDA subclass of glutamate receptors in that no increase was observed in the responses to two other glutamate agonists, kainate and AMPA (alpha‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionic acid). 5. Stimulation of PKC by activation of metabotropic receptors via either quisqualate or trans‐ACPD (trans‐1‐aminocyclopentane‐1,3‐dicarboxylic acid) also led to an increase in NMDA currents. 6. Both methods of enhancement induced transient effects. PDBu effects lasted 10‐45 min, depending upon both dose and length of application. Quisqualate and trans‐ACPD effects were shorter, lasting less than 10 min under these conditions of application. 7. Both methods of enhancement were blocked by the PKC inhibitor, staurosporine. In addition, the phorbol ester‐induced enhancement of NMDA responses occluded further enhancement by quisqualate. 8. The results suggest a role for metabotropic glutamate receptors in modulation of NMDA‐mediated processes.
A quantitative account of the activation steps involved in phototransduction in amphibian photoreceptors.
Authors: Lamb T D , Pugh E N
Published: December 2014

1. We have undertaken a theoretical analysis of the steps contributing to the phototransduction cascade in vertebrate photoreceptors. We have explicitly considered only the activation steps, i.e. we have not dealt with the inactivation reactions. 2. From the theoretical analysis we conclude that a single photoisomerization leads to activation of the phosphodiesterase (PDE) with a time course which approximates a delayed ramp; the delay is contributed by several short first‐order delay stages. 3. We derive a method for extracting the time course of PDE activation from the measured electrical response, and we apply this method to recordings of the photoresponse from salamander rods. The results confirm the prediction that the time course of PDE activation is a delayed ramp, with slope proportional to light intensity; the initial delay is about 10‐20 ms. 4. We derive approximate analytical solutions for the electrical response of the photoreceptor to light, both for bright flashes (isotropic conditions) and for single photons (involving longitudinal diffusion of cyclic GMP in the outer segment). The response to a brief flash is predicted to follow a delayed Gaussian function of time, i.e. after an initial short delay the response should begin rising in proportion to t2. Further, the response‐intensity relation is predicted to obey an exponential saturation. 5. These predictions are compared with experiment, and it is shown that the rising phase of the flash response is accurately described over a very wide range of intensities. We conclude that the model provides a comprehensive description of the activation steps of phototransduction at a molecular level.
Relative mitochondrial membrane potential and [Ca2+]i in type I cells isolated from the rabbit carotid body.
Authors: Duchen M R , Biscoe T J
Published: December 2014

1. In the accompanying paper (Duchen & Biscoe, 1992) we have described graded changes in autofluorescence derived from mitochondrial NAD(P)H in type I cells of the carotid body in response to changes of PO2 over a physiologically significant range. These observations suggest that mitochondrial function in these cells is unusually sensitive to oxygen and could play a role in oxygen sensing. We have now explored further the relationships between hypoxia, mitochondrial membrane potential (delta psi m) and [Ca2+]i. 2. The fluorescence of Rhodamine 123 (Rh 123) accumulated within mitochondria is quenched by delta psi m. Mitochondrial depolarization thus increases the fluorescence signal. Blockade of electron transport (CN‐, anoxia, rotenone) and uncoupling agents (e.g. carbonyl cyanide p‐trifluoromethoxy‐phenylhydrazone; FCCP) increased fluorescence by up to 80‐120%, while fluorescence was reduced by blockade of the F0 proton channel of the mitochondrial ATP synthase complex (oligomycin). 3. delta psi m depolarized rapidly with anoxia, and was usually completely dissipated within 1‐2 min. The depolarization of delta psi m with anoxia (or CN‐) and repolarization on reoxygenation both followed a time course well characterized as the sum of two exponential processes. Oligomycin (0.2‐2 micrograms/ml) hyperpolarized delta psi m and abolished the slower components of both the depolarization with anoxia and of the subsequent repolarization. These data (i) illustrate the role of the F1‐F0 ATP synthetase in slowing the rate of dissipation of delta psi m on cessation of electron transport, (ii) confirm blockade of the ATP synthetase by oligomycin at these concentrations, and (iii) indicate significant accumulation of intramitochondrial ADP during 1‐2 min of anoxia. 4. Depolarization of delta psi m was graded with graded changes in PO2 below about 60 mmHg. The stimulus‐response curves thus constructed strongly resemble those for [Ca2+]i and NAD(P)H with PO2. The change in delta psi m closely followed changes in PO2 with time. 5. The rate of rise of [Ca2+]i in response to anoxia is strongly temperature sensitive. The rate of depolarization of delta psi m with anoxia similarly increased at least two‐ to fivefold on warming from 22 to 36 degrees C. The change with FCCP was not significantly altered by temperature. 6. These data show that the mitochondrial membrane potential changes over a physiological range of PO2 values in type I cells. This contrasts with the behaviour in dissociated chromaffin cells and sensory neurons, in which no change was measurable until the PO2 fell close to zero.(ABSTRACT TRUNCATED AT 400 WORDS)
Quantal transmitter release mediated by strontium at the mouse motor nerve terminal.
Authors: Bain A I , Quastel D M
Published: December 2014

1. In isolated mouse diaphragm, nerve stimulation in the presence of Sr2+ evokes phasic quantal transmitter release (endplate potentials, EPPs) with the same time course as in the presence of Ca2+. 2. Brief tetanic trains of nerve stimuli in the presence of Sr2+ cause an increase in quantal content of EPPs accompanied by an increase in the frequency of miniature EPPs (MEPPs); the latter persists as a ‘tail’ that subsides within about a second. Pseudo‐random stimulation sequences were used to characterize these changes. 3. The fourth root of MEPP frequency during or after stimulation rose and fell in accordance with first order kinetics with the same time constants for rising and falling phases, in agreement with a ‘residual ion’ model in which (a) each nerve impulse causes the same entry of Sr2+ into the nerve terminal, (b) transmitter release (MEPP frequency) is proportional to the fourth power of [Sr2+] at release sites, and (c) Sr2+ removal is a first order process with a time constant of about 250 ms. 4. After exposure to bis (O‐aminophenoxy)ethane‐N,N,N’,N'‐tetraacetic acid, acetoxymethyl ester form (BAPTA AM), ‘Sr2+ tails’ of MEPP frequency were reduced in magnitude and prolonged. 5. During stimulation trains, growth of phasic transmitter release rates (and quantal content of EPPs) were related to growth of MEPP frequency in almost exact agreement with a residual ion model, in which ‘phasic’ release (EPPs) and MEPP frequency are governed by the same equation, with the same parameters, and without any effect of depolarization per se to affect phasic release. 6. Prolonged (1 s) nerve terminal depolarizations in the presence of Sr2+ produce increased MEPP frequency with a time course corresponding to a model in which depolarization per se has little or no effect to increase transmitter release. 7. It was concluded that in the presence of Sr2+ the intense ‘phasic’ acceleration of quantal release induced by nerve impulse manifest in an EPP can be attributed to a transient rise of intracellular [Sr2+] in the vicinity of release sites, while the modulation of ‘phasic’ release by antecedent nerve impulses can be attributed to residual Sr2+ which is also manifest in a rise in MEPP frequency.
Two types of neurone in the rat ventral tegmental area and their synaptic inputs.
Authors: Johnson S W , North R A
Published: December 2014

1. Intracellular recordings were made from 241 ventral tegmental neurones in slices of rat midbrain. Seventy‐seven per cent of neurones were hyperpolarized by dopamine (principal cells); 16% were hyperpolarized by opioid peptides (secondary cells). 2. Most principal cells fired spontaneously (1‐3 Hz) with a threshold of ‐53 mV; most secondary cells did not fire spontaneously. Action potentials of principal cells were longer (0.9 ms) than those of secondary cells (0.5 ms). 3. Focal electrical stimulation within the ventral tegmental area evoked a biphasic synaptic potential, depolarization followed by hyperpolarization, with a duration of about 200 ms. Experiments with receptor antagonists showed that the depolarizing component resulted from activation of both N‐methyl‐D‐aspartate (NMDA) and non‐NMDA receptors and the hyperpolarizing component resulted from activation of GABAA receptors. 4. A later hyperpolarizing synaptic potential developed after a latency of 50 ms, reached its peak in 250 ms and had a duration of about 1 s. It reversed polarity at ‐108 mV (external potassium concentration was 2.5 mM), was blocked by phaclofen (30 microM‐1 mM) or 2‐hydroxysaclofen (100‐300 microM). In some cells, a phaclofen‐resistant component remained that was increased by cocaine and blocked by sulpiride (1 microM). 5. It is concluded that the ventral tegmental area contains two types of neurone having properties similar to those in the substantia nigra. The cells receive synaptic inputs mediated by excitatory amino acids acting at NMDA and non‐NMDA receptors, GABA acting at GABAA and GABAB receptors, and dopamine acting at D2 receptors.
Spontaneous sarcoplasmic reticulum calcium release and extrusion from bovine, not porcine, coronary artery smooth muscle.
Authors: Stehno‐Bittel L , Sturek M
Published: December 2014

1. We tested the hypothesis that the Ca(2+)‐loaded sarcoplasmic reticulum (SR) of coronary artery smooth muscle spontaneously releases Ca2+ preferentially toward the sarcolemma to be extruded from the cell without increasing the average free myoplasmic [Ca2+] (Ca(im)) concentration. 2. The SR of bovine cells was Ca(2+)‐loaded by depolarization‐induced Ca2+ influx. Release (unloading) of Ca2+ from the SR during recovery from depolarization was determined by Fura‐2 microfluorometry of Ca(im). The SR Ca2+ unloading was maximal following a long (14 min) recovery from depolarization, as shown by the 66% decrease in the peak caffeine‐induced Ca(im) transient compared to the Ca(im) transient after a short (2 min) recovery. No increase in Ca(im) occurred during the long recovery. No unloading of the SR Ca2+ store was noted in porcine cells. 3. Approximately 80% of the outward K+ current in bovine and porcine cells was sensitive to subsarcolemmal Ca2+ (Ca(is)) concentrations. Whole‐cell voltage clamp using pipette solutions with Ca2+ concentrations clamped between 0 and 1000 nM with Ca(2+)‐EGTA or Ca(2+)‐BAPTA buffers showed increasing K+ currents (normalized for cell membrane surface area) as a function of both membrane potential and Ca(is). Clamping of Ca(im) and Ca(is) was verified by the lack of changes in K+ current and Fura‐2 ratio in response to Ca2+ influx, Ca(2+)‐free external solution, or caffeine‐induced Ca2+ release. At +30 to +50 mV the K+ current amplitude showed a similar sensitivity to Ca2+ as Fura‐2. These data indicate that in this experimental preparation Ca(2+)‐activated K+ current is a valid estimate of Ca(is). 4. Simultaneous Ca(im) and Ca(is) measurements in bovine cells which were not Ca(2+)‐clamped (2 x 10(‐4) M‐EGTA pipette solution) showed that during the long recovery period the K+ current (reflecting Ca(is)) increased 55%, while Ca(im) did not change. 5. In quiescent bovine cells the Ca(is) was higher than Ca(im), while the higher resting Ca(is) gradient was not apparent in porcine cells. 6. The Ca(is) concentration was directly related to the amount of Ca2+ in the SR in bovine, but not porcine cells. Depletion of the SR in bovine cells by caffeine resulted in a 58% decrease in K+ current compared to the resting K+ current. 7. Caffeine‐induced Ca2+ release caused an increase in Ca(is) which preceded the increase in Ca(im) by approximately 2 s.(ABSTRACT TRUNCATED AT 400 WORDS)
Kinetic and pharmacological properties of the M‐current in rodent neuroblastoma x glioma hybrid cells.
Authors: Robbins J , Trouslard J , Marsh S J , Brown D A
Published: December 2014

1. The M‐like current IK(M,ng) in differentiated NG108‐15 mouse neuroblastoma x rat glioma hybrid cells has been studied using tight‐seal, whole‐cell patch‐clamp recording. 2. When calculated from steady‐state current‐voltage curves, the conductance underlying IK(M,ng) showed a Boltzmann dependence on voltage with half‐activation voltage Vo = ‐44 mV (in 3 mM [K+]) and slope factor (a) = 8.1 mV/e‐fold increase in conductance. In 12 mM [K+] Vo = ‐38 mV and a = 6.9 mV. The deactivation reciprocal time constant accelerated with hyperpolarization with slope factor 17 mV/e‐fold voltage change. 3. The reversal potential for deactivation tail currents varied with external [K+] as if PNa/PK were 0.005. 4. Steady‐state current was increased on removing external Ca2+. In the presence of external Ca2+, reactivation of IK(M, ng) after a hyperpolarizing step was delayed. This delay was preceded by an inward Ca2+ current, and coincided with an increase in intracellular [Ca2+] as measured with Indo‐1 fluorescence. Elevation of intracellular [Ca2+] with caffeine also reduced IK(M, ng). 5. IK(M, ng) was inhibited by external divalent cations in decreasing order of potency (mM IC50 in parentheses): Zn2+ (0.011) greater than Cu2+ (0.018) greater than Cd2+ (0.070) greater than Ni2+ (0.44) greater than Ba2+ (0.47) greater than Fe2+ (0.69) greater than Mn2+ (0.86) greater than Co2+ (0.92) greater than Ca2+ (5.6) greater than Mg2+ (16) greater than Sr2+ (33). This was not secondary to inhibition of ICa since: (i) inhibition persisted in Ca(2+)‐free solution; (ii) La3+ did not inhibit IK(M, ng) at concentrations which inhibited ICa; and (iii) organic Ca2+ channel blockers were ineffective. Inhibition comprised both depression of the maximum conductance and a positive shift of the activation curve. Addition of Ca2+ (10 microM free [Ca2+]) or Ba2+ (1 mM total [Ba2+]) to the pipette solution did not significantly change IK(M, ng). 6. IK(M, ng) was reduced by 9‐amino‐1,2,3,4‐tetrahydroacridine (IC50 8 microM) and quinine (30 microM) but was insensitive to tetraethylammonium (IC50 greater than 30 mM), 4‐aminopyridine (greater than 10 mM), apamin (greater than 3 microM) or dendrotoxin (greater than 100 nM). 7. IK(M, ng) was inhibited by bradykinin (1‐10 microM) or angiotensin II (1‐10 microM), but not by the following other receptor agonists: acetylcholine (10 mM), muscarine (10 microM), noradrenaline (100 microM), adrenaline (100 microM), dopamine (100 microM), histamine (100 microM), 5‐hydroxytryptamine (10 microM), Met‐enkephalin (1 microM), glycine (100 microM), gamma‐aminobutyric acid (100 microM) or baclofen (500 microM).(ABSTRACT TRUNCATED AT 400 WORDS)