bluuebunny/crossref_metadata_2025 huggingface dataset:
Serotonin inhibits Ca2+ currents in porcine melanotrophs by activating 5‐HT1C and 5‐HT1A receptors.
Authors: Ciranna L , Mouginot D , Feltz P , Schlichter R
Published: December 2014

1. We have investigated the effect of serotonin (5‐HT) on Ca2+ currents in cultured porcine pituitary intermediate lobe (IL) cells. Electrophysiological recordings were performed in the whole‐cell configuration of the patch‐clamp technique. All membrane currents other than Ca2+ currents were blocked pharmacologically and by ionic substitution. 2. Two types of Ca2+ currents were recorded in IL cells, differing by their activation and inactivation properties. The first type of Ca2+ current was activated at membrane potentials more positive than ‐60 mV and had a transient time course during the 100 ms depolarizing voltage steps. The properties of this current correspond to those of the T‐type or low‐voltage‐activated Ca2+ current. The second type of Ca2+ current had a threshold for activation between ‐30 and ‐20 mV and showed no sign of inactivation with time during the voltage steps. The properties of this current are similar to those of the L‐type or high‐voltage‐activated Ca2+ current. 3. Current to voltage (I‐V) relationships obtained either by conventional 100 ms voltage steps from a holding potential (VH) of ‐100 mV to various test potentials or by 800 ms voltage ramps from ‐100 to +50mV matched one another closely and showed two inward current humps corresponding to the activation of the T‐type and L‐type Ca2+ currents respectively. The ramp protocol was used to characterize the effect of 5‐HT on the Ca2+ current I‐V relationship. 4. 5‐HT (100nM to 50 microM) reversibly inhibited the amplitude of the Ca2+ current triggered by 100 ms voltage jumps from a Vh of ‐100 mV to a test potential of 0 mV. 5. The effect of 5‐HT was dose dependent with a threshold between 10 and 100 nM and a maximal effect at 10 microM. At a concentration of 10 microM, the average inhibition of Ca2+ current by 5‐HT was 18.3 +/‐ 6.5% (n = 27). 5‐HT inhibited Ba2+ current in a similar fashion. 6. When examining the effect of 5‐HT on Ca2+ current I‐V relationships, we observed a reversible inhibition of the high‐threshold component corresponding to the L‐type Ca2+ current. We never observed any effect of 5‐HT on the T‐type current. 7. The effect of 5‐HT (10 microM) was antagonized to various extents by mianserin (1 microM) but not by ketanserin (0.1 microM), suggesting the involvement of 5‐HT1C receptors.(ABSTRACT TRUNCATED AT 400 WORDS)
Noradrenergic modulation of retinogeniculate transmission in the cat.
Authors: Funke K , Pape H C , Eysel U T
Published: December 2014

1. Relay neurones were extracellularly recorded from the A‐layers of the dorsal lateral geniculate nucleus (dLGN) of the anaesthetized cat. The noradrenergic influence on retinogeniculate transmission was investigated through microiontopheretic techniques in a total of 140 dLGN relay cells using three experimental approaches: (i) the effects of agonists for alpha 1‐, alpha 2‐ and beta‐adrenoceptors were separately analysed; (ii) the noradrenergic influence was related to the global state of activity of the relay neurones, which was associated with discrete patterns of the electroencephalogram (EEG); (iii) distinct phases of visual responses evoked from the area of the retinal receptive field, and of binocular and lateral inhibitory responses, were evaluated before, during and after the action of noradrenergic agonists. 2. The spontaneous generation of high‐frequency bursts of spikes in dLGN relay neurones, associated with periods of highly synchronized, delta‐like patterns of the EEG, was selectively suppressed by the beta‐adrenoceptor agonist isoprenaline or the alpha 1‐ adrenoceptor agonist phenylephrine. Single action potentials, occurring at a low frequency between bursts, were significantly less affected. Depending upon the ejection level of the adrenoceptor agonists, burst activity was suppressed by 23‐73%, compared with a reduction in single spike firing in the range 7‐24%. The suppression of burst firing occurred in all functional types of dLGN relay neurones (X, Y; on, off), enhanced burst activity was observed in less than 1% of the cells. 3. On‐going tonic sequences of action potentials (around 15 Hz), occurring during periods of EEG activity characterized by lower amplitudes and higher frequencies, were separately affected by adrenoceptor agonists. Isoprenaline had no significant effect, phenylephrine induced a global reduction of spike firing with no obvious relation to the ejection level, and the alpha 2‐adrenoceptor agonist clonidine inhibited action potential generation in a near dose‐dependent manner. 4. Visual response properties were investigated during periods of less synchronized states of EEG activity. Responses to visual stimulation of the retinal receptive field centre were not significantly influenced by isoprenaline, while phenylephrine or clonidine attenuated the phasic and the tonic response component in all functional types of relay neurones and independent of the stimulus contrast being used. At low ejection levels, slight facilitatory effects were observed with isoprenaline (65% of neurones that were tested) or phenylephrine (15%). The inhibitory influence of the antagonistic surround area of the receptive field appeared unaltered during action of isoprenaline or phenylephrine.(ABSTRACT TRUNCATED AT 400 WORDS)
Cellular mechanism of acetylcholine‐induced response in dissociated outer hair cells of guinea‐pig cochlea.
Authors: Kakehata S , Nakagawa T , Takasaka T , Akaike N
Published: December 2014

1. The acetylcholine (ACh)‐induced currents (IACh) in dissociated outer hair cells (OHCs) of guinea‐pig cochlea were investigated using the whole‐cell patch‐clamp technique, in both conventional and nystatin perforated‐patch configurations. 2. ACh and carbamylcholine (CCh) induced outward currents at a holding potential (VH) of ‐60 mV in the perforated‐patch configuration. The IACh increased in a sigmoidal fashion over the concentration range between 3 x 10(‐6) and 10(‐3) M. The dissociation constant (KD) was 1.7 x 10(‐5) M and the Hill coefficient (n) was 2.7. The KD and n for CCh were 8.7 x 10(‐5) M and 2.2, respectively. Neither nicotine nor muscarine induced any detectable current up to a concentration of 10(‐3) M. 3. Various muscarinic agonists such as oxotremorine‐M, McN‐A‐343 and oxotremorine could also induce the outward currents, although these current amplitudes were about one‐third that of ACh, indicating that they were partial agonists. 4. The muscarinic antagonists atropine, 4‐DAMP, AF‐DX 116 and pirenzepine inhibited the IACh in a concentration‐dependent manner. The half‐inhibitory concentrations (IC50) for atropine, 4‐DAMP, AF‐DX 116 and pirenzepine were 4.8 x 10(‐6), 6.2 x 10(‐6), 2.1 x 10(‐5) and 2.9 x 10(‐4) M, respectively. 5. When the extracellular Ca2+ concentration ([Ca2+])o) was reduced to lower than 1 mM, the amplitude of IACh, abruptly decreased. In a nominally Ca(2+)‐free external solution ACh did not induce any current. The increase of [Ca2+]o beyond 1 mM did not change the IACh. 6. When OHCs were perfused intracellularly with a pipette solution containing 10 mM BAPTA in the conventional whole‐cell mode, ACh could not induce outward K+ currents. The Ca2+ ionophore A23187 induced an outward current. These results indicate that intracellular Ca2+ is involved in the ACh response. 7. Calmodulin inhibitors such as chlorpromazine, W‐7 and trifluoperazine inhibited the IACh in a concentration‐dependent manner. 8. When OHCs were dialysed with either 100 microM GDP beta S or 1 micrograms/ml pertussis toxin (PTX) through the patch pipette at a VH of ‐60 mV, the IACh diminished within 10 min, whereas the IACh of the control remained steady for over 20 min, suggesting that a PTX‐sensitive G‐protein is involved in the ACh response.(ABSTRACT TRUNCATED AT 400 WORDS)
Modulation of acetylcholine‐elicited currents in clonal rat phaeochromocytoma (PC12) cells by internal polyphosphates.
Authors: Ifune C K , Steinbach J H
Published: December 2014

1. Whole‐cell voltage clamp techniques were used to examine acetylcholine (ACh)‐elicited currents in differentiated cells of the rat phaeochromocytoma cell line, PC12. 2. In the absence of intracellular Mg2+, the whole‐cell current‐voltage relationship for the ACh‐elicited current displayed inward rectification which was reduced in part by the presence of 5 mM internal adenosine 5'‐triphosphate (ATP). 3. The reduction in the rectification attributed to ATP developed over the first 15‐20 min of whole‐cell recording. Similar results were obtained with a non‐hydrolysable ATP analogue, adenosine‐5'‐O‐3‐thiotriphosphate (ATP gamma S), or cytosine 5'‐triphosphate (CTP) in the internal solution, but not with adenosine 5'‐diphosphate (ADP) or pyrophosphate. 4. The magnitude of the ACh‐elicited current was also dependent on recording time and the composition of the internal pipette solution. The magnitude of the peak ACh‐elicited current increased over time when the cell was internally perfused with the control solution or a pipette solution containing pyrophosphate, ATP gamma S, or ADP. The largest sustained increases in ACh‐elicited current were observed in the presence of internal pyrophosphate or ATP gamma S. In contrast, with internal ATP or CTP, the whole‐cell current initially increased, then steadily decreased with recording time. 5. The desensitization rate of the ACh‐elicited current increased with recording time irrespective of the composition of the intracellular solution. 6. The actions of the compounds tested make it likely that the changes in the whole‐cell current‐voltage relationship, peak current, and desensitization are produced by separate mechanisms. The mechanisms underlying these changes are unknown, but the ability of the compounds to chelate divalent cations is unlikely to be the explanation. Other unlikely explanations include phosphorylation of the ACh receptor or regulation by GTP‐binding proteins.
Hyperpolarizing muscarinic responses of freshly dissociated rat hippocampal CA1 neurones.
Authors: Wakamori M , Hidaka H , Akaike N
Published: December 2014

1. Intracellular mechanisms of the muscarinic acetylcholine (ACh) response were investigated in pyramidal neurones freshly dissociated from the rat hippocampal CA1 region. Current recordings were made in the whole‐cell mode using the nystatin ‘perforated’‐patch technique, by which the muscarinic ACh response can be continuously recorded without so‐called ‘run‐down’ phenomenon. The amount of intracellular free Ca2+ ([Ca2+]i) was fluorometrically measured using fura‐2. 2. In current clamp conditions, ACh induced a transient hyperpolarization accompanied by a decrease in membrane input resistance. 3. Under voltage clamp conditions at a holding potential (Vh) of ‐40 mV, ACh induced two types of muscarinic currents observed either alone or together: a transient outward current and a slowly activating sustained inward current. 4. The ACh‐induced transient outward current reversed the direction at K+ equilibrium potential (EK), and the reversal potential (EACh) shifted 56.7 mV for a tenfold change of extracellular K+ concentration ([K+]o). 5. The ACh‐induced transient outward current increased in a sigmoidal fashion with increase in ACh concentration, where the half‐maximal concentration (EC50) and the Hill coefficient (n) were 8 x 10(‐7) M and 1.9, respectively. Both muscarine and carbamylcholine mimicked the ACh response, but neither McN‐A‐343 (M1 agonist) nor oxotremorine (cardiac M2 agonist) induced any current. 6. Muscarinic antagonists reversibly blocked the ACh response in a concentration‐dependent manner. The inhibitory potency was in the order of atropine > pirenzepine > AF‐DX‐116. 7. The ACh‐induced transient outward current was never recorded when [Ca2+]i was chelated by the acetoxymethyl ester form of 1,2‐bis(O‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid (BAPTA AM). On the other hand, in Ca(2+)‐free external solution containing 2 mM EGTA and 10 mM Mg2+, the ACh response was elicited by the first application and successive ACh applications did not induce any response. Fura‐2 imaging showed that [Ca2+]i was increased when ACh was added to the external medium with or without Ca2+, though in Ca(2+)‐free medium only the first application of ACh increased the [Ca2+]i. 8. The ACh response was not affected by pretreatment with pertussis toxin (PTX) but the inhibitory effect of ACh on the high‐threshold Ca2+ channel was abolished completely. 9. Pretreatment with Li+ enhanced the amplitude of the transient outward current and the increase in [Ca2+]i induced by ACh. 10. The calmodulin antagonists W‐7, chlorpromazine and trifluoperazine reversibly inhibited the ACh response in a concentration‐dependent manner.(ABSTRACT TRUNCATED AT 400 WORDS)
Thapsigargin‐evoked changes in human platelet Ca2+, Na+, pH and membrane potential.
Authors: Kimura M , Lasker N , Aviv A
Published: December 2014

1. In this work we explored the effect of thapsigarin on the intracellular Ca2+, pH, Na+ and membrane potential in human platelets. These parameters were monitored using the fluorescent probes fura‐2, 2',7'‐bis‐(2‐carboxyethyl)‐5,6‐carboxyfluorescein, sodium‐binding benzofuran isophthalate, and 3,3'‐dipropylthiadicarbocyanine iodide. 2. Thapsigargin caused an increase in the cytosolic Ca2+, coupled with cytosolic alkalinization. Thapsigargin‐induced alkalinization was Na(+)‐dependent, indicating that thapsigargin stimulated the Na(+)‐H+ exchange. 3. Using Mn2+ as a Ca2+ surrogate, we showed that thapsigargin activated Ca2+ channels at relatively low levels of cytosolic Ca2+, suggesting that a rise in cytosolic free Ca2+ is not the signal for the activation of these channels. 4. Thapsigargin‐induced increase in the cytosolic free Ca2+ was greater in Na(+)‐containing medium than in Na(+)‐free medium, suggesting that Na(+)‐dependent mechanisms participate in the regulation of platelet cytosolic Ca2+. 5. Thapsigargin not only increased the cytosolic Ca2+, but also elevated the cytosolic free Na+. The latter effect was more pronounced in Ca(2+)‐free medium, a finding that may indicate that some of the Na+ enters through Ca2+ entry pathways. 6. Finally, thapsigargin evoked sustained platelet hyperpolarization which was attenuated by charybdotoxin, indicating thapsigargin‐induced stimulation of Ca(2+)‐sensitive K+ channels. 7. Together these observations demonstrate a multifactorial effect of thapsigargin on platelets that can be utilized to further understand platelet ionic homeostasis.
Multiple effects of spermine on N‐methyl‐D‐aspartic acid receptor responses of rat cultured hippocampal neurones.
Authors: Benveniste M , Mayer M L
Published: December 2014

1. The modulation by polyamines of responses to N‐methyl‐D‐aspartic acid (NMDA) was studied using a rapid perfusion system and whole‐cell voltage‐clamp recording from rat hippocampal neurons in dissociated culture. 2. Concentration jump responses to 100 microM NMDA in the presence of 10 microM glycine revealed potentiation by 3 mM spermine at a membrane potential of +60 mV, but depression at ‐120 mV; the degree of potentiation at +60 mV was variable from cell to cell while marked depression at ‐120 mV was observed in all cells. The depression of responses to NMDA by spermine was highly voltage dependent (z delta = 1.17) with an apparent equilibrium dissociation constant for block at 0 mV of 27 mM. 3. Analysis of spermine dose‐potentiation curves for responses recorded at +60 mV in the presence of 10 microM glycine revealed a half‐maximal effect at 125 microM. Under the same conditions, but at ‐60 mV, analysis of spermine‐evoked depression was performed for cells with less than 5% potentiation at +60 mV, and revealed half‐maximal inhibition at 344 microM. 4. Dose‐response analysis for the glycine‐sensitive activation of NMDA receptors at +60 mV revealed a 3.5‐fold increase in apparent affinity for glycine in the presence of 1 mM spermine. This increase in affinity for glycine was accompanied by a 3.3‐fold decrease in the rate of development of glycine‐sensitive desensitization, and a 2.4‐fold decrease in the rate of dissociation of glycine from NMDA receptors, while the rate constant for dissociation of NMDA was not reduced. 5. In the presence of non‐saturating concentrations of glycine, spermine‐induced potentiation at +60 mV developed with two exponential components: a slow glycine‐sensitive component, the amplitude and time constant of which decreased with increasing glycine concentration (30 nM glycine, amplitude = 80.2 +/‐ 5.1%, tau = 780 +/‐ 79 ms; 3 microM glycine, amplitude = 22.6 +/‐ 7.1%, tau = 45 +/‐ 13 ms), and a faster component (tau < 20 ms at all concentrations of glycine), the amplitude of which varied from cell to cell, and which became larger with increase in concentration of glycine. When responses to the application of spermine were measured in the presence 10 microM L‐alanine instead of 100 nM glycine, the slow component of potentiation was absent.(ABSTRACT TRUNCATED AT 400 WORDS)
On the excitatory effects of ATP and its role as a neurotransmitter in coeliac neurons of the guinea‐pig.
Authors: Silinsky E M , Gerzanich V
Published: December 2014

1. The effects of ATP on neurons from guinea‐pig coeliac ganglia were studied to evaluate the possibility that this nucleotide acts as an excitatory neurotransmitter substance. 2. In experiments with intracellular microelectrodes, ATP (> or = 10 nM) depolarized coeliac neurons from the resting potential and produced an increase in the membrane conductance. These excitatory effects of ATP were observed in isolated coeliac ganglia, in acutely dissociated neurons or in cultured neurons. ATP also produced membrane conductance increases in neurons clamped at the resting potential using a single electrode voltage clamp. 3. When studied in the whole‐cell configuration of the patch clamp (intracellular Cs+ to block K+ currents; ‐50 mV holding potential), ATP evoked inward currents in a manner more potent and efficacious than acetylcholine (ACh). 4. Whole‐cell currents induced by ATP were inwardly rectifying and reversed at ‐13 mV in normal Na+ solutions. Changes in extracellular Na+ concentration altered the reversal potential in a manner predicted by the Goldman‐Hodgkin‐Katz bi‐ionic equation with a ratio of Na+ to Cs+ permeability (PNa/PCs) = 0.6. 5. Single channel currents were evoked by ATP in excised (outside‐out) patches. Current‐voltage relationships for single channel currents exhibited inward rectification. The mean single channel conductance was 22 pS at ‐50 mV. 6. Antagonists of ATP‐gated channels (suramin, Reactive Blue 2) reduced the effects of ATP but not ACh. 7. Antagonists at nicotinic receptors/ion channels (hexamethonium or tubocurarine) reduced the effects of ACh but not ATP. 8. Excitatory synaptic currents were observed in cultures of coeliac neurons. Synaptic currents possessed similar current‐voltage relationships to currents produced by ATP, were increased in frequency by K+ depolarization in a Ca(2+)‐dependent manner, and were selectively antagonized by ATP antagonists. 9. Local K+ depolarization of the ends of neurites evoked single channel currents characteristic of ATP in outside‐out patches when patches were positioned near the region of apparent synaptic contact but not when patches were positioned at remote regions. 10. The results suggest that ATP receptors are linked to ion channels and mediate excitatory synaptic transmission between coeliac neurons.
Membrane properties of rat suprachiasmatic nucleus neurons receiving optic nerve input.
Authors: Kim Y I , Dudek F E
Published: December 2014

1. The electrophysiological properties of suprachiasmatic nucleus (SCN) neurons (n = 33) receiving optic nerve input were studied with intracellular recordings in rat hypothalamic slices maintained in vitro. Our major goal was to provide baseline data concerning the intrinsic membrane properties of these neurons and to test the hypothesis that the neurons are homogeneous electrophysiologically. 2. Action potentials were short in duration and followed by a pronounced hyperpolarizing after‐potential. Spike amplitude (58.2 +/‐ 1.1 mV, mean +/‐ S.E.M.; measured from threshold), spike duration (0.83 +/‐ 0.03 ms; measured at half amplitude) and hyperpolarizing after‐potential amplitude (23.9 +/‐ 1.0 mV; measured from threshold) appeared unimodally distributed and did not co‐vary. 3. Intracellular injection of depolarizing current pulses evoked spike trains, and spike inactivation, spike broadening and frequency accommodation were always present. An after‐hyperpolarization followed the spike train in all but one neuron. 4. Membrane time constant ranged from 7.5 to 21.1 ms (11.4 +/‐ 0.7 ms, n = 27), and its distribution appeared to be unimodal with the peak at approximately 10 ms. Input resistance ranged from 105 to 626 M omega (301 +/‐ 23 M omega, n = 33); the distribution also appeared unimodal with its peak at approximately 250 M omega. 5. A subpopulation (16 of 33, 48%) of the neurons exhibited slight (6‐29%) time‐dependent inward rectification in their voltage responses to hyperpolarizing current injection. Of the neurons lacking the time‐dependent rectification, some (n = 5) exhibited time‐independent inward rectification of 6‐20% and others showed no (or < 3%) such rectification. The degree of inward rectification was correlated with neuronal excitability (r = 0.60, P < 0.002; assessed by measuring the steepness of the primary slope of the frequency‐current plot) and with the spontaneous firing rate (r = 0.49, P < 0.007). Furthermore, the neurons with > 6% inward rectification (neurons with time‐dependent and ‐independent rectification were combined) were more excitable (362 +/‐ 43 Hz/nA (n = 15) vs. 221 +/‐ 37 Hz/nA (n = 9), P < 0.05) and had a higher spontaneous firing rate (11.1 +/‐ 1.9 Hz (n = 19) vs. 3.9 +/‐ 1.5 Hz (n = 11), P < 0.02) than the neurons with no or negligible (i.e. < 3%) inward rectification. The two groups, however, were not significantly different in membrane time constant and input resistance. 6. When adequately hyperpolarized, twelve of seventeen (71%) neurons generated small low‐threshold spike (LTS) potentials in response to depolarizing current pulses.(ABSTRACT TRUNCATED AT 400 WORDS)
Characteristics of Ca2+ release induced by Ca2+ influx in cultured bullfrog sympathetic neurones.
Authors: Hua S Y , Nohmi M , Kuba K
Published: December 2014

1. A rise in intracellular Ca2+ ([Ca2+]i) and a Ca2+ current (ICa) induced by a depolarizing pulse were simultaneously recorded by fura‐2 or indo‐1 fluorescence and whole‐cell patch clamp techniques in cultured bullfrog sympathetic ganglion cells. 2. [Ca2+]i (calculated from the ratio of fura‐2 fluorescences excited at 380 and 340 nm and recorded with a photomultiplier at > 492 nm) rose regeneratively (in most cells) during a command pulse (from ‐60 to 0 mV, 100 ms), continued to rise thereafter, peaked at 666 ms (on average) and decayed slowly with a half‐decay time of 22.8 s. 3. Scanning a single horizontal line across the cytoplasm with an ultraviolet argon ion laser (351 nm) and recording indo‐1 fluorescences at two wavelengths (peaked at 410 and 475 nm) with a confocal microscope demonstrated that [Ca2+]i beneath the cell membrane rose much faster than that in the deeper cytoplasm. The time course of the spatial integral of [Ca2+]i, however, corresponded well with that recorded with fura‐2 fluorescence using a photomultiplier. 4. [Ca2+]i measured by fura‐2 fluorescence ratio using a photomultiplier did not increase during a strong depolarizing pulse (‐60 to +80 mV), but sometimes rose after the pulse. A depolarization‐induced rise in [Ca2+]i ([Ca2+]i transient) was blocked in a Ca(2+)‐free, EGTA solution, reduced by lowering the extracellular Ca2+ concentration ([Ca2+]o) to 0.45 or 0.9 mM and enhanced by raising [Ca2+]o to 7.2 or 14.4 nM. 5. The extracellular Ca2+ dependence was non‐linear when long depolarizing pulses (up to 500 ms) were applied; the amplitude of [Ca2+]i transient/Ca2+ entry (unit [Ca2+]i transient) increased with an increase in Ca2+ entry. 6. Increasing the duration of depolarization (‐50 or ‐60 to 0 mV) from 20 to 500 ms enhanced asymptotically the integral of ICa (due to inactivation), and progressively the magnitude of [Ca2+]i transients, leading to the apparent non‐linear dependence of unit [Ca2+]i transient on Ca2+ entry as well as on the duration of membrane depolarization. The peak time of [Ca2+]i transient was unchanged for pulse durations up to 300 ms, but prolonged with an increase in pulse duration to 500 ms. 7. Inhibitors of Ca2+ release from intracellular Ca2+ reservoirs, dantrolene (10 microM) and ryanodine (50 microM), blocked the [Ca2+]i transient to 56 and 30%, respectively, of the control. 8. The higher the basal [Ca2+]i level, the greater was the magnitude of the [Ca2+]i transients.(ABSTRACT TRUNCATED AT 400 WORDS)
Task dependence of responses in first dorsal interosseous muscle to magnetic brain stimulation in man.
Authors: Flament D , Goldsmith P , Buckley C J , Lemon R N
Published: December 2014

1. The response of the first dorsal interosseous (1DI) muscle to non‐invasive magnetic and scalp electrical stimulation of the brain have been investigated during performance of different manual tasks. 2. The six tasks tested required activation of the 1DI muscle, either in isolation (during abduction of the index finger) or as part of a more complex pattern of muscle synergies (e.g. during power grip). The level of 1DI EMG activity across tasks was kept constant by providing subjects with visual feedback of their muscle activity. 3. In every subject (n = 14) magnetic stimulation produced larger responses during performance of complex tasks than during the simple index abduction task. The pooled results from all subjects showed that four of the five complex tasks were associated with significantly larger 1DI responses (paired t test, P < 0.05). 4. These results were confirmed at the single motor unit level for nine motor units recorded from six subjects. Subjects were requested to produce a steady discharge of the same motor unit during performance of different tasks. The probability of motor unit discharge in response to magnetic stimulation was significantly greater during complex tasks (rotation or pincer grips) than during abduction. 5. Scalp electrical stimulation was performed in three subjects with the cathode at the vertex and the anode over the contralateral motor cortex. The pattern of response amplitudes in the different tasks tended to parallel that obtained for magnetic stimulation, but the task‐related differences were smaller. 6. These results suggest that during performance of the different tasks, the corticospinal volleys evoked by magnetic stimulation may vary in amplitude. The task‐related cortical mechanisms that may contribute to this variability are discussed.
Chloride currents activated by caffeine in rat intestinal smooth muscle cells.
Authors: Ohta T , Ito S , Nakazato Y
Published: December 2014

1. Current responses to caffeine in single smooth muscle cells isolated from rat intestine were studied with the whole‐cell patch clamp technique. Intracellular calcium concentration, [Ca2+]i, was simultaneously monitored with fura‐2 (0.1 mM) introduced into the cell through a patch pipette. 2. With a potassium‐containing pipette solution, caffeine (10 mM) produced an outward current at a holding potential of 0 mV and an inward current at ‐60 mV, both of which were accompanied by parallel increases in [Ca2+]i. The outward current response disappeared after the removal of K+ from pipette solutions, indicating that caffeine activates a Ca(2+)‐activated K+ conductance. 3. When NaCl was present in both pipette and external solutions as the major constituent, caffeine evoked an inward current at ‐60 mV simultaneously with a rise in [Ca2+]i. The reversal potential (Er) of this current was about 0 mV. 4. Substitution of Tris+ or choline+ for external Na+ did not alter the Er. When external Cl‐ was replaced by thiocyanate‐, iodide‐ or glutamate‐, the Er changed to respectively ‐55, ‐38 and +35 mV. 5. The current response to caffeine decreased with increasing concentration of EGTA in the pipette solution. The caffeine‐induced current and the intracellular Ca2+ transient was still observed for a few minutes after exposure of the cells to Ca(2+)‐free external solution containing 2 mM EGTA. Caffeine failed to produce an inward current and Ca2+ transient after treatment with extracellular ryanodine. 6. It is concluded that caffeine caused an increase in membrane Cl‐ conductance and in K+ conductance resulting from a rise in [Ca2+]i derived from ryanodine‐sensitive intracellular Ca2+ stores in isolated smooth muscle cells of the rat intestine.
Visual transduction in dialysed detached rod outer segments from lizard retina.
Authors: Rispoli G , Sather W A , Detwiler P B
Published: December 2014

1. Properties of a new preparation for studying the physiology and biochemistry of phototransduction in retinal rods are described. Whole‐cell voltage clamp was used to record the generation, maintenance and light‐sensitivity of dark current in rod outer segments that had been isolated from the rest of the receptor cell by detachment at the connecting cilium. 2. Detached outer segments dialysed with standard internal solution supplemented with physiological amounts of ATP (5 mM) and GTP (1 mM) developed a standing inward dark current that was the sum of three components: approximately 91% light‐sensitive current, approximately 6% Na(+)‐Ca2+,K+ exchange current and approximately 3% leakage current. Light‐sensitive dark current (mean amplitude approximately ‐63 pA) was suppressed transiently by brief flashes in an intensity‐dependent manner. Light responses had the same kinetics, sensitivity and intensity‐response relationship as those recorded from intact rods. 3. Dialysed outer segments differed from intact rods in that intense flashes evoked saturating responses that recovered incompletely to a plateau of reduced dark current caused by incomplete inactivation of the transduction cascade. Light sensitivity was reduced for a short time following an intense flash and then recovered despite persistent reduction of dark current. This suggests that there is no fixed relationship between dark current amplitude and light sensitivity. 4. Light‐sensitive dark current faded rapidly when outer segments were not supplied with nucleotides. Outer segments dialysed with solution that contained cyclic GMP, but no ATP or GTP, supported dark current at a level that increased with [cyclic GMP]. When basal phosphodiesterase (PDE) activity is inhibited, 8 microM cyclic GMP supports a dark current of approximately 70 pA. 5. Light sensitivity decreased during recordings made with solution that contained only cyclic GMP, consistent with the inhibition of G protein activation by loss of GTP. After thorough nucleoside triphosphate depletion, however, intense illumination evoked a transient increase rather than a decrease in dark current, i.e. an inverted light response. This result suggests that isomerized rhodopsin may generate a signal that causes either inhibition of basal PDE activity or release of bound cyclic GMP. 6. Sustained Na(+)‐Ca2+,K+ exchange current was recorded during steady illumination when Ca2+, but not when Mg2+, was added to the dialysis solution. Exchange current increased with the amount of added Ca2+ and saturated at approximately 18 pA when the dialysis solution contained > or = 10 mM Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)
Action of histamine on single smooth muscle cells dispersed from the rabbit pulmonary artery.
Authors: Wang Q , Large W A
Published: December 2014

1. The effects of histamine, noradrenaline and caffeine were studied in freshly dispersed smooth muscle cells from the rabbit pulmonary artery using the perforated patch technique. 2. In potassium‐containing solutions at a holding potential of ‐50 mV all three agents evoked net inward and outward currents. At 0 mV only an outward current was observed and this response was not produced in potassium‐free conditions. 3. In K(+)‐free solutions the reversal potential (Er) of the inward current was dependent upon the transmembrane anion gradient but not on the cation gradient. Thus all three agents produced an increase in potassium and chloride conductance. 4. Bath‐applied histamine evoked repetitive potassium and chloride currents in many cells. Bath‐applied noradrenaline and caffeine, to a lesser extent, also caused repetitive currents but the brief ionophoretic application of noradrenaline never produced oscillations in membrane current. 5. Histamine reduced or abolished the amplitude of spontaneous transient potassium and chloride currents. 6. Histamine‐induced currents were blocked by caffeine (10 mM) but could be recorded in Ca(2+)‐free bathing solutions. 7. It is concluded that in the rabbit pulmonary artery histamine evokes single and oscillatory membrane potassium and chloride currents which are mediated by the release of calcium from intracellular caffeine‐sensitive stores.
Inositol trisphosphate‐mediated Ca2+ influx into Xenopus oocytes triggers Ca2+ liberation from intracellular stores.
Authors: Yao Y , Parker I
Published: December 2014

1. Inositol 1,4,5‐trisphosphate (InsP3) functions as a second messenger by liberating Ca2+ from intracellular stores and by promoting influx of extracellular Ca2+. We examined whether Ca2+ influx modulates intracellular Ca2+ liberation in Xenopus oocytes by fluorescence monitoring of cytosolic free Ca2+ together with voltage clamp recording of Ca(2+)‐activated Cl‐ membrane currents. Sustained activation of membrane Ca2+ permeability was induced by intracellular injections of a non‐metabolizable InsP3 analogue, 3‐deoxy‐3‐fluoro‐D‐myo‐inositol 1,4,5‐trisphosphate (3‐F‐InsP3), and Ca2+ influx was controlled by applying step changes in membrane potential to alter the driving force for Ca2+ entry. 2. Negative‐going potential steps evoked intracellular Ca2+ signals comprising two components; an initial transient peak followed by a slower rise. The initial transient grew steeply over a narrow (ca 40 mV) voltage range but then increased little with further polarization, whereas the second component showed a nearly linear voltage dependence. 3. The transient Ca2+ signal continued to rise almost unchanged when Ca2+ influx was interrupted by stepping the potential to more positive values after brief hyperpolarization. In contrast, Ca2+ levels declined monotonically when positive‐going steps were applied after longer intervals during the second component of the Ca2+ signal. 4. Large Ca(2+)‐dependent transient inward (T(in)) membrane currents were evoked during the rising phase of the initial Ca2+ signal, but little current was associated with the second component of the Ca2+ signal. 5. The T(in) currents evoked by hyperpolarization were mimicked at fixed clamp potential by re‐admitting Ca2+ to the bathing solution, and by flash photolysis of caged Ca2+ loaded into the oocyte. 6. T(in) currents were strongly inhibited by prior release of Ca2+ from InsP3‐sensitive intracellular stores, and vice versa. Experiments with paired hyperpolarizing pulses and paired photorelease of InsP3 showed that responses to both stimuli recovered with similar time courses. 7. We conclude that the transient Ca2+ signal and associated T(in) current evoked by hyperpolarization arise because Ca2+ entering the oocyte triggers regenerative release of Ca2+ from InsP3‐sensitive intracellular stores. Since membrane currents evoked by liberated Ca2+ were much greater than those evoked by Ca2+ entry per se, a major function of InsP3‐mediated Ca2+ entry may be to modulate the activity of intracellular Ca2+ stores.
Intracellular calcium and vasopressin release of rat isolated neurohypophysial nerve endings.
Authors: Stuenkel E L , Nordmann J J
Published: December 2014

1. Monitoring of [Ca2+]i and vasopressin secretion in isolated nerve endings from the rat neurohypophysis were studied to determine the relationship between the time course of vasopressin secretion and depolarization‐induced changes in [Ca2+]i. 2. Membrane depolarization by increasing the extracellular [K+] led to concentration‐dependent, parallel increases in the amount of vasopressin release and in peak increases in [Ca2+]i. Half‐maximal activation of a change in [Ca2+]i was attained at 40 mM extracellular K+. 3. The Ca2+ chelator dimethyl‐BAPTA (1,2‐bis(O‐aminophenoxy)ethane‐N,N,N'N'‐tetraacetic acid), loaded into the nerve endings, reduced K+ depolarization‐evoked vasopressin release and efficiently antagonized K(+)‐induced changes in [Ca2+]i. Moreover, dimethyl‐BAPTA dramatically reduced basal [Ca2+]i without a reduction in basal secretion. 4. The duration of the vasopressin secretory response was similar regardless of applied 50 mM K+ depolarizations longer than 30 s. The t1/2 of the secretory response was 45 s. Application of repetitive K+ depolarization pulses repetitive secretory responses of similar amplitude and duration. 5. The K(+)‐induced changes in [Ca2+]i remained elevated throughout the duration of the depolarizing stimulus decreasing less than 30% over 3 min. The sustained increase in [Ca2+]i resulted largely from continued enhanced Ca2+ influx, demonstrated by susceptibility to the dihydropyridine, L‐type calcium channel blocker, nicardipine. 6. Vasopressin secretion could be reinitiated following its decline to a step K+ depolarization by a further step increase in K+ or by removal and readdition of extracellular [Ca2+]. Alterations in [Ca2+]i paralleled periods of secretory activity. 7. Analysis of secretory responsiveness and change in [Ca2+]i to K+ depolarization in medium of altered extracellular [Ca2+] indicates that [Ca2+]i of 20 microM is sufficient to trigger vasopressin release. K(+)‐induced alterations in [Ca2+]i could be observed at [Ca2+]o as low as 5 microM. Although smaller in amplitude to that observed at 2.2 mM [Ca2+]o the duration of the K(+)‐induced secretory response increased at lower [Ca2+]o. 8. Transient vasopressin secretory responses were observed to sustained levels of [Ca2+] in digitonin and streptolysin‐O‐permeabilized nerve endings. Secretion could be re‐evoked, following its decline, by a step increase in [Ca2+] or by removal and readdition of [Ca2+]o.(ABSTRACT TRUNCATED AT 400 WORDS)
Effect of bradykinin on respiratory rate in anaesthetized rabbits; role of rapidly adapting receptors.
Authors: Hargreaves M , Ravi K , Kappagoda C T
Published: December 2014

1. This study was performed in anaesthetized, spontaneously breathing rabbits: (a) to determine the effect of bradykinin administered into the right atrium on the respiratory rate, and (b) to elucidate the potential role of rapidly adapting receptors (RARs) in mediating this effect. The role of RARs was established by graded cooling of the cervical vagi. The respiratory rate was measured from an intrapleural pressure tracing. 2. Dose‐response curves relating right atrial injections of bradykinin (0.25, 0.5, 1.0 and 1.5 micrograms/kg) to the respiratory rate were established in the control state (i.e. vagi at 37 degrees C). The respiratory rate increased significantly (P < 0.01, ANOVA) from a control value of 51.3 +/‐ 6.8 breaths/min by 12 +/‐ 3, 25 +/‐ 5, 43 +/‐ 7 and 58 +/‐ 11% respectively. At doses of 1.0 and 1.5 micrograms/kg I.V., the increase in rate was preceded by apnoea. 3. The dose‐response curves were repeated with bolus injections of bradykinin (0.25, 0.5, 1.0 and 1.5 micrograms/kg) after cooling the cervical vagi to 8‐9 degrees C. The increase in respiratory rate was attenuated significantly (P < 0.01 ANOVA). The rate increased from a control value of 27.2 +/‐ 2.1 breaths/min by 5 +/‐ 2, 6 +/‐ 2, 16 +/‐ 5 and 21 +/‐ 8% respectively. With vagi cooled, apnoea was increased in duration and occurred at lower doses. On rewarming vagi, the original responses were reestablished. 4. When the study was repeated after bilateral vagotomy, apnoea was abolished but there was a small residual increase in rate. This increase was similar to that seen after cooling the vagi (P > 0.05). 5. RAR (n = 5) activity was recorded from the cervical vagus. Right atrial injections of bradykinin (0.25‐1.0 micrograms/kg) stimulated RARs. On cooling the vagi to 8‐9 degrees C caudal to the recording site, the increase in activity was blocked. 6. These data support the proposition that bradykinin increases the respiratory rate in rabbits and that this response is, in part, a reflex mediated by RARs. In addition, bradykinin has other secondary effects on respiration: an aponea which is mediated by non‐myelinated vagal afferents and a small stimulatory effect on respiration which persists after bilateral vagotomy.
Mercury blockage of apical water channels in toad skin (Bufo marinus).
Authors: Grosso A , De Sousa R C
Published: December 2014

1. Net water flow (Jw) was continuously monitored across the abdominal skin of the toad Bufo marinus by means of a volumetric, automatic technique. Jw was either averaged over periods of 2 min or taken cumulatively (10 or 30 min periods). 2. The state of high water permeability induced by vasopressin or isoprenaline was reversed (88‐89% inhibition of delta Jw after 1 h) by the addition of 10(‐3) M HgCl2 (or CH3ClHg) to the external bathing medium. Similarly, pre‐exposure of the skins to Hg2+, totally blocked the induction of the hydrosmotic response to the same agents. By itself, Hg2+ exerted only a minor (26%) stimulation of basal Jw. 3. There was a sigmoidal dose‐response relationship between the reduction of the hydrosmotic effect of vasopressin (VP) and the concentration of Hg2+ in the external medium, with a half‐maximal effect at 1.2 x 10(‐4) M HgCl2. 4. Total replacement of Na+ by K+, Rb+ or Cs+ in the Ringer solution, caused a VP‐like, hydrosmotic effect that was reversed, or prevented, by exposure to Hg2+ in a manner indistinguishable from that previously seen with vasopressin or isoprenaline. 5. The data point to the presence of a Hg(2+)‐sensitive apical water pathway in stimulated epithelia, very probably constituted by water channels similar to those reported in red blood cells, amphibian bladder and mammalian kidney tubules.
Correlation of primate red nucleus discharge with muscle activity during free‐form arm movements.
Authors: Miller L E , van Kan P L , Sinkjaer T , Andersen T , Harris G D , Houk J C
Published: December 2014

1. We recorded from 239 neurons located in the magnocellular division of the red nucleus of four alert macaque monkeys. At the same time, we recorded electromyographic (EMG) signals from as many as twenty electrodes chronically implanted on muscles of the shoulder, arm, forearm and hand. We recorded EMG signals for periods ranging from several months to a year. 2. The monkeys were trained to perform three free‐form food retrieval tasks, each of which activated all of the recorded muscles and most of the neurons. The ‘prehension’ task required simply that the monkey grasp a piece of food from a fixed point in space. The ‘barrier’ task required the monkey to reach around a small barrier to obtain the food, and the ‘Kluver’ task required that food be removed from small holes. During the prehension task, we found approximately equal numbers of neurons that were strongly active while the hand was being moved toward the target (70% of units), and while the food was being grasped (60%). Relatively few units were active as the hand was returned to the mouth (15%). 3. Data files of 1‐2 min duration were collected while the monkey performed a single behavioural task. Whenever possible, we recorded files for all three tasks from each neuron. For each file we calculated long time‐span analog cross‐correlations (+/‐ 1.28 s) between instantaneous neuronal firing rate and each of the full‐wave rectified, low‐pass filtered EMG signals. We used the peak correlation and the time of the peak as two summary measures of the functional relation between modulation of neuronal activity and EMG. 4. The magnitude of the strongest correlations was between 0.4 and 0.5 (normalized to a perfect correlation of +/‐ 1.0). Distal muscles were the most frequently correlated, and extensors were more frequently correlated than flexors. For all monkeys, the lags for well correlated muscles were distributed broadly about a uni‐modal value near 0 ms. Eighty five per cent of the correlations larger than or equal to 0.25 had peaks between ‐150 and 200 ms. 5. The activity of each neuron was represented in a muscle co‐ordinate system by an n‐dimensional ‘functional linkage vector’, each element of which was the peak correlation with one of n muscles. The vector for any given neuron points in a particular direction in muscle space, depending on the similarity between the activity of the neuron and the activity of each muscle.(ABSTRACT TRUNCATED AT 400 WORDS)
Regulation of unloaded cell shortening by sarcolemmal sodium‐calcium exchange in isolated rat ventricular myocytes.
Authors: Bouchard R A , Clark R B , Giles W R
Published: December 2014

1. Regulation of unloaded cell shortening and relaxation by sarcolemmal Na(+)‐Ca2+ exchange was investigated in rat ventricular myocytes. Contraction of single cells at 22 +/‐ 1 degrees C was measured simultaneously with membrane current and voltage using the whole‐cell voltage clamp technique in combination with a video edge‐detection device. 2. The extent of mechanical activation (cell shortening amplitude) was strongly dependent on diastolic membrane potential over the voltage range ‐140 to ‐50 mV. This voltage sensitivity of contraction was abolished completely when a recently described inhibitory peptide of the cardiac Na(+)‐Ca2+ exchanger (XIP, 2 x 10(‐5) M) was present in the recording pipette, demonstrating that in rat ventricular cells Na(+)‐Ca2+ exchange is modulated by diastolic membrane potential. 3. Possible influences of Na(+)‐Ca2+ exchange on contraction were studied from a holding potential of ‐80 mV. Depolarizations (‐50 to +60 mV) resulted in a bell‐shaped shortening‐voltage (S‐V) relationship. These contractions were suppressed completely by either Cd2+ (10(‐4) M) or verapamil (10(‐5) M), but remained unchanged during superfusion with tetrodotoxin (TTX, 1.5 x 10(‐5) M), when [NA+]o was reduced from 140 to 10 mM by substitution with either Li+ or Cs+ ions or when pipette Na+ was varied between 8 and 13 mM. XIP (2 x 10(‐5) M) increased the magnitude and duration of twitch contractions, but had no effect on the shape of the S‐V relationship. Thus, the Ca2+ current but not the Na+ current or Ca2+ influx due to reversed Na(+)‐Ca2+ exchange can release Ca2+ from the sarcoplasmic reticulum (SR) under these experimental conditions. 4. The effect of the rate of repolarization on cell shortening was studied under voltage clamp by applying ramp waveforms immediately following the depolarizations which activated contraction. Although slowing of the rate of repolarization had no effect on the first contraction following a train of conditioning depolarizations, a positive inotropic effect developed thereafter. 5. Caffeine (10 mM) was applied to determine whether Na(+)‐Ca2+ exchange and/or Ca2+ sequestration/buffering by the sarcoplasmic reticulum were primarily responsible for these inotropic effects. In the presence of caffeine the positive inotropic effect developed fully during the first test depolarization. Changes in the rate of repolarization had much less effect on shortening in cells dialysed intracellularly with XIP (2 x 10(‐5) M). In combination, these results suggest that the changes in the inotropic effects resulting from changes in rate of repolarization may be due to altered loading and release of Ca2+ from the SR.(ABSTRACT TRUNCATED AT 400 WORDS)