bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hypoxia and cyanide induce depolarization and catecholamine release in dispersed guinea‐pig chromaffin cells
Authors: Inoue M. , Fujishiro N. , Imanaga I. 
Published: September 2004

The perforated patch method and amperometry were used to determine whether the adrenal medullary cell itself is capable of sensing hypoxia and, if so, how such sensation is transduced to secretion of catecholamines (CA).
Exposure to hypoxia, cyanide (CN), or muscarine facilitated CA secretion from dissociated chromaffin cells. The CN‐induced secretion was not affected by removal of glucose, indicating that the CN release is due to chemical hypoxia.
The secretions induced by CN and muscarine were markedly diminished by removal of Ca2+ ions or by application of Cd2+ or methoxyverapamil (D‐600).
Cyanide and muscarine produced depolarizations with generation of action potentials and increased intracellular Ca2+ concentrations determined using the acetoxymethyl (AM) ester form of fluo‐3 in the presence of external Ca2+ ions, but not in their absence.
Hypoxia and CN produced inward currents at an equilibrium potential for Cl− ions, irrespective of whether or not Na+ ions were present in the cells, and substitution of N‐methyl‐D‐glucamine for 134 mM Na+ ions in the perfusate inhibited the CN current by 71 %. The reversal potential for the CN current was −24 mV in the standard perfusate.
The hypoxia‐, CN‐ and muscarine‐induced currents decreased in parallel with hyperpolarizations, and exposure to CN prevented muscarine, but not nicotine, from inducing a further inward current.
We conclude that hypoxia and CN induce CA secretion through depolarization and the subsequent activation of voltage‐dependent Ca2+ channels and that this depolarization is due to opening of cation channels, which are possibly identical to muscarinic cation channels.
Repolarizing K+ currents in rabbit heart Purkinje cells
Authors: Cordeiro J. M. , Spitzer K. W. , Giles W. R. 
Published: September 2004

Electrophysiological experiments on single myocytes obtained from Purkinje fibres and ventricular tissue of adult rabbit hearts were done to compare the contributions of three potassium (K+) currents to the action potentials in these two tissues.
In Purkinje cells reductions in extracellular potassium, [K+]o, from normal (5.4 mM) to 2.0 mM resulted in a large hyperpolarization and marked lengthening of the action potential. In ventricular myocytes, these changes were much less pronounced. Voltage clamp measurements demonstrated that these differences were mainly due to a much smaller inward rectifier K+ current, IK1, in Purkinje cells than in ventricular myocytes.
Application of 4‐aminopyridine (4‐AP, 2 mM) showed that all Purkinje cells exhibited a very substantial Ca2+‐independent transient K+ outward current, It. 4‐AP significantly broadened the early, rapid repolarization phase of the action potential.
Selective inhibitors of the fast component, IK,r (MK‐499, 200 nM) and the slow component IK,s (L‐735821 (propenamide), 20 nM) of the delayed rectifier K+ currents both significantly lengthened the action potential, suggesting that these conductances are present, but very small (< 20 pA) in Purkinje cells. Attempts to identify time‐ and voltage‐dependent delayed rectifier K+ current(s) in Purkinje cells failed, although a slow delayed rectifier was observed in ventricular myocytes.
These results demonstrate significant differences in action potential waveform, and underlying K+ currents in rabbit Purkinje and ventricular myocytes. Purkinje cells express a much smaller IK1, and a larger It than ventricular myocytes. These differences in current densities can explain some of the most important electrophysiological properties of these two tissues.
Activation of L‐arginine transport by protein kinase C in rabbit, rat and mouse alveolar macrophages
Authors: Racké Kurt , Hey Claudia , Mössner Jutta , Hammermann Rainer , Stichnote Christina , Wessler Ignaz 
Published: September 2004

The role of protein kinase C in controlling L‐arginine transport in alveolar macrophages was investigated.
L‐[3H]Arginine uptake in rabbit alveolar macrophages declined by 80 % after 20 h in culture. 4β‐Phorbol 12‐myristate 13‐acetate (PMA), but not 4α‐phorbol 12‐myristate 13‐acetate (α‐PMA), present during 20 h culture, enhanced L‐[3H]arginine uptake more than 10‐fold. Staurosporine and chelerythrine opposed this effect.
L‐[3H]Arginine uptake was saturable and blockable by L‐lysine. After PMA treatment Vmax was increased more than 5‐fold and Km was reduced from 0.65 to 0.32 mM.
Time course experiments showed that PMA increased L‐[3H]arginine uptake almost maximally within 2 h. This short‐term effect was not affected by cycloheximide or actinomycin D.
L‐[3H]Arginine uptake and its stimulation by PMA was also observed in sodium‐free medium.
L‐Leucine (0.1 mM) inhibited L‐[3H]arginine uptake by 50 % in sodium‐containing medium, but not in sodium‐free medium. At 1 mM, L‐leucine caused significant inhibition in sodium‐free medium also. L‐Leucine showed similar effects on PMA‐treated cells.
N‐Ethylmaleimide (200 μm, 10 min) reduced L‐[3H]arginine uptake by 70 % in control cells, but had no effect on PMA‐treated (20 or 2 h) cells.
In alveolar macrophages, multiple transport systems are involved in L‐arginine uptake, which is markedly stimulated by protein kinase C, probably by modulation of the activity of already expressed cationic amino acid transporters.
Metabotropic and ionotropic glutamate receptors regulate calcium channel currents in salamander retinal ganglion cells
Authors: Shen Wen , Slaughter Malcolm M. 
Published: September 2004

Glutamate suppressed high‐voltage‐activated barium currents (IBa,HVA) in tiger salamander retinal ganglion cells. Both ionotropic (iGluR) and metabotropic (mGluR) receptors contributed to this calcium channel inhibition.
Trans‐ACPD (1‐aminocyclopentane‐trans‐1S,3R‐dicarboxylic acid), a broad‐spectrum metabotropic glutamate receptor agonist, suppressed a dihydropyridine‐sensitive barium current. Kainate, an ionotropic glutamate receptor agonist, reduced an ω‐conotoxin GVIA‐sensitive current.
The relative effectiveness of selective agonists indicated that the predominant metabotropic receptor was the L‐2‐amino‐4‐phosphonobutyrate (L‐AP4)‐sensitive, group III receptor. This receptor reversed the action of forskolin, but this was not responsible for calcium channel suppression. l‐AP4 raised internal calcium concentration. Antagonists of phospholipase C, inositol trisphosphate (IP3) receptors and ryanodine receptors inhibited the action of metabotropic agonists, indicating that group III receptor transduction was linked to this pathway.
The action of kainate was partially suppressed by BAPTA, by calmodulin antagonists and by blockers of calmodulin‐dependent phosphatase. Suppression by kainate of the calcium channel current was more rapid when calcium was the charge carrier, instead of barium. The results indicate that calcium influx through kainate‐sensitive glutamate receptors can activate calmodulin, which stimulates phosphatases that may directly suppress voltage‐sensitive calcium channels.
Thus, ionotropic and metabotropic glutamate receptors inhibit distinct calcium channels. They could act synergistically, since both increase internal calcium. These pathways provide negative feedback that can reduce calcium influx when ganglion cells are depolarized.
Potentiation of GABAergic synaptic transmission by AMPA receptors in mouse cerebellar stellate cells: changes during development
Authors: Bureau Ingrid , Mulle Christophe 
Published: September 2004

The effects of low concentrations of domoate, an agonist at both α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate and kainate receptors (AMPARs and KARs, respectively), were investigated in stellate cells in slices of mouse cerebellum at two developmental stages (postnatal day (PN) 11‐13 and PN21‐25).
Low concentrations of domoate enhanced the frequency of miniature IPSCs (mIPSCs) recorded in the presence of tetrodotoxin (TTX) at PN11‐13 but not at PN21‐25.
The effects of low concentrations of domoate on synaptic activity were probably mediated by the activation of AMPARs and not KARs, since they were blocked by GYKI 53655 (LY300168), a selective AMPAR antagonist.
Domoate increased mIPSC frequency in part by activation of presynaptic voltage‐dependent Ca2+ channels since potentiation was reduced by 60 % in the presence of Cd2+. AMPARs in stellate cells were found to be permeable to Ca2+. The residual potentiation in the presence of Cd2+ could thus be due to a direct entry of Ca2+ through AMPAR channels.
In the presence of TTX, potentiation of synaptic activity by focal application of domoate was not restricted to the region of the cell body, but was observed within distances of 120 μm. These experiments also revealed a strong spatial correlation between the location of the presynaptic effects of domoate and the activation of postsynaptic AMPARs.
Our data show a developmentally regulated presynaptic potentiation of synaptic transmission between cerebellar interneurones mediated by AMPARs. We discuss the possibility that the developmental switch could be due to a shift in the localization of AMPARs from the axonal to the somato‐dendritic compartment.
Effects of mitochondrial uncouplers on intracellular calcium, pH and membrane potential in rat carotid body type I cells
Authors: Buckler K. J. , Vaughan‐Jones R. D. 
Published: September 2004

Mitochondrial uncouplers are potent stimulants of the carotid body. We have therefore investigated their effects upon isolated type I cells. Both 2,4‐dinitrophenol (DNP) and carbonyl cyanide p‐trifluoromethoxyphenyl hydrazone (FCCP) caused an increase in [Ca2+]i which was largely inhibited by removal of extracellular Ca2+ or Na+, or by the addition of 2 mm Ni2+. Methoxyverapamil (D600) also partially inhibited the [Ca2+]i response.
In perforated‐patch recordings, the rise in [Ca2+]i coincided with membrane depolarization and was greatly reduced by voltage clamping the cell to −70 mV. Uncouplers also inhibited a background K+ current and induced a small inward current.
Uncouplers reduced pHi by 0.1 unit. Alkaline media diminished this acidification but had no effect on the [Ca2+]i response.
FCCP and DNP also depolarized type I cell mitochondria. The onset of mitochondrial depolarization preceded changes in cell membrane conductance by 3–4 s.
We conclude that uncouplers excite the carotid body by inhibiting a background K+ conductance and inducing a small inward current, both of which lead to membrane depolarization and voltage‐gated Ca2+ entry. These effects are unlikely to be caused by cell acidification. The inhibition of background K+ current may be related to the uncoupling of oxidative phosphorylation.
Cl− transport by cystic fibrosis transmembrane conductance regulator (CFTR) contributes to the inhibition of epithelial Na+ channels (ENaCs) in Xenopus oocytes co‐expressing CFTR and ENaC
Authors: Briel M. , Greger R. , Kunzelmann K. 
Published: September 2004

Epithelial Na+ channels (ENaCs) are inhibited by the cystic fibrosis transmembrane conductance regulator (CFTR) when CFTR is activated by protein kinase A. Since cAMP‐dependent activation of CFTR Cl− conductance is defective in cystic fibrosis (CF), ENaC currents are not inhibited by CFTR. This could explain the enhanced Na+ conductance found in CF. In the present study, we examined possible mechanisms of interaction between CFTR and ENaC co‐expressed in Xenopus oocytes.
The magnitude of CFTR Cl− currents activated by 3‐isobutyl‐1‐methylxanthine (IBMX) in oocytes co‐expressing either wild‐type or mutant CFTR and ENaC determined the degree of downregulation of ENaC currents.
The ability of CFTR to inhibit ENaC currents was significantly reduced either when extracellular Cl− was replaced by poorly conductive anions, e.g. SCN− or gluconate, or when CFTR was inhibited by diphenylamine‐carboxylate (DPC, 1 mmol l−1).
Downregulation of ENaC was more pronounced at positive when compared with negative clamp voltages. This suggests that outward currents, i.e. influx of Cl− through activated CFTR most effectively downregulated ENaC.
Activation of endogenous Ca2+‐activated Cl− currents by 1 μmol l−1 ionomycin did not inhibit ENaC current. This suggests that inhibition of ENaC mediated by Cl− currents may be specific to CFTR.
The present findings indicate that downregulation of ENaC by CFTR is correlated to the ability of CFTR to conduct Cl−. The data have implications for how epithelia switch from NaCl absorption to NaCl secretion when CFTR is activated by secretagogues.
Interruption of central noradrenergic pathways and morphine withdrawal excitation of oxytocin neurones in the rat
Authors: Brown C. H. , Murphy N. P. , Munro G. , Ludwig M. , Bull P. M. , Leng G. , Russell J. A. 
Published: September 2004

We have tested the hypothesis that morphine withdrawal excitation of oxytocin neurones that follows from administration of naloxone to morphine‐dependent rats is a consequence of excitation of noradrenergic neurones.
Female rats were made morphine dependent by intracerebroventricular (i.c.v.) infusion of the opioid at increasing doses over 5 days. On the sixth day, the rats were anaesthetized with urethane or pentobarbitone and prepared for blood sampling to determine plasma oxytocin by radioimmunoassay or for in vivo extracellular recording of the firing rate of identified oxytocin neurones from the supraoptic nucleus. Morphine withdrawal was induced by intravenous (i.v.) injection of the opioid antagonist naloxone (5 mg kg−1).
In one group of rats the noradrenergic projections to the hypothalamus were lesioned by i.c.v. injection of 6‐hydroxydopamine immediately prior to the induction of morphine dependence. In these rats the oxytocin secretion induced by i.v. cholecystokinin was reduced to 9 % of that seen in sham‐lesioned rats but in contrast, no attenuation of morphine withdrawal‐induced oxytocin secretion was observed.
i.c.v. infusion of the α1‐adrenoreceptor antagonist benoxathian, at up to 5.3 μg min−1, dose‐ dependently inhibited the withdrawal excitation of oxytocin neurones in morphine‐dependent rats under urethane anaesthesia, and benoxathian reduced withdrawal‐induced oxytocin secretion to 37 % of that of vehicle‐infused rats. i.c.v. benoxathian also inhibited the activity of oxytocin neurones in morphine‐naïve rats. Similarly, microdialysis administration of 2 mM benoxathian directly onto the surface of the supraoptic nucleus reduced the activity of oxytocin neurones by 53 %.
Thus noradrenergic systems are not essential for the expression of morphine withdrawal excitation, since chronic neurotoxic destruction of the noradrenergic inputs to the hypothalamus did not affect the magnitude of withdrawal‐induced oxytocin secretion. However, tonically active noradrenergic inputs influence the excitability of oxytocin neurones, and acute antagonism of this noradrenergic tone can powerfully impair the ability of oxytocin neurones to exhibit morphine withdrawal excitation.
Kainate receptor‐mediated inhibition of presynaptic Ca2+ influx and EPSP in area CA1 of the rat hippocampus
Authors: Kamiya Haruyuki , Ozawa Seiji 
Published: September 2004

The effect of a low concentration (1 μM) of kainate (kainic acid; KA) on presynaptic calcium (Ca2+) influx at the Schaffer collateral‐commissural (SCC) synapse was examined in rat hippocampal slices.
Following selective loading of the presynaptic terminals with the fluorescent Ca2+ indicator rhod‐2 AM, transient increases in the presynaptic Ca2+ concentration (pre[Ca2+]t) and field excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of the SCC pathway were recorded simultaneously.
Bath application of 1 μM KA reversibly suppressed field EPSPs and pre[Ca2+]t to 37.7 ± 4.0 % and 72.9 ± 2.4 % of control, respectively. Excitatory postsynaptic currents (EPSCs) recorded with the use of the whole‐cell patch‐clamp technique were also suppressed by 1 μM KA to 42.6 ± 6.3 % of control. A quantitative analysis of the decreases in pre[Ca2+]t and the amplitude of field EPSP during KA application suggests that KA inhibits transmission primarily by reducing the pre[Ca2+]t.
Consistent with a presynaptic site for these effects, paired‐pulse facilitation (PPF) was enhanced by 1 μM KA.
A substantial KA‐induced suppression of NMDA receptor‐mediated EPSPs was detected when AMPA receptors were blocked by the AMPA receptor‐selective antagonist GYKI 52466 (100 μM).
The suppressive effect of KA on field EPSPs and pre[Ca2+]t was antagonized by the KA antagonist NS‐102 (10 μM).
These results suggest that the presynaptic inhibitory action of KA at the hippocampal CA1 synapse is primarily due to the inhibition of Ca2+ influx into the presynaptic terminals.
Chloride‐sensitive nature of the histamine‐induced Ca2+ entry in cultured human aortic endothelial cells
Authors: Ono Kyoichi , Nakao Miki , Iijima Toshihiko 
Published: September 2004

Whole‐cell currents and intracellular Ca2+ concentration ([Ca2+]i) were recorded in cultured human aortic endothelial cells (HAECs) to study the mechanisms underlying Cl−‐sensitive Ca2+ entry.
In the absence of histamine the membrane potential ranged between ‐90 and +5 mV and showed bimodal distribution with peaks at ‐17.8 and ‐67.5 mV.
Histamine (1‐100 μm) activated an outward current, followed by a sustained inward current at ‐50 mV. The reversal potential (Vrev) was more negative than ‐60 mV for the initial outward current, and approximately ‐30 mV for the sustained inward current with normal Tyrode solution and internal solution containing 30 mM Cl−.
V
rev of the sustained inward current was hardly affected by varying the external concentrations of K+, Na+ and Ca2+, but was greatly changed by varying the external Cl− concentration ([Cl−]o). The relationship between Vrev and log[Cl−]o showed a slope of ‐44.8 mV per tenfold increase of [Cl−]o.
The Cl− channel blockers 9‐anthracene carboxylic acid (1 mM), N‐phenylanthranilic acid (0.1 mM) and niflumic acid (0.1 mM) all depressed the histamine‐induced inward current. The non‐selective cation channel blocker Gd3+ (10 μm) was without effect on the current.
In the absence of histamine, [Ca2+]i was not affected by varying the membrane potential. During the continuous presence of histamine, however, hyperpolarization increased and depolarization decreased [Ca2+]i, indicating that Ca2+ entry through the plasma membrane was activated by histamine.
V
rev of the histamine‐induced Cl− current, measured by the gramicidin‐perforated patch clamp method, was ‐28.4 ± 6.6 mV (n= 8), which gave an intracellular Cl− concentration of approximately 34 mM. Under the current clamp condition, the membrane potential varied from cell to cell in the control, but application of histamine induced either depolarization or hyperpolarization, depending on the membrane potential before histamine application, and the membrane potential became stable near the equilibrium potential for Cl−.
We conclude that the histamine‐induced inward current is carried mainly by Cl−. Although Ca2+ entry was also activated, we consider that its amplitude was too small to be resolved by the patch clamp method. The Cl− current may play a functional role in the sustained [Ca2+]i elevation by providing a constant driving force for Ca2+ entry in the presence of histamine.
Presynaptic adrenergic facilitation of parasympathetic neurotransmission in sympathectomized rat smooth muscle
Authors: Krizsan‐Agbas Dora , Zhang Renjie , Marzban Farshid , Smith Peter G. 
Published: September 2004

Parasympathetic innervation of rat eyelid tarsal smooth muscle normally inhibits sympathetic neurotransmission prejunctionally without significant direct postjunctional effects. Following surgical sympathectomy, parasympathetic stimulation elicits smooth muscle contraction. This study examined the relative contributions of cholinergic and adrenergic mechanisms mediating these contractions.
Electrical stimulation of the superior salivatory nucleus, which activates tarsal muscle parasympathetic nerves, elicited large contractions at 2 days postsympathectomy, which were abolished by atropine and were decreased by 65 % by α1‐adrenoceptor blockade or spinal cord transection.
Contractions in response to direct cholinergic stimulation by bethanechol at 2 days postsympathectomy were increased following spinal cord transection (C2) and suppressed by the α1‐adrenoceptor agonist phenylephrine, indicating that adrenoceptors on smooth muscle attenuate cholinergic contractions. However, phenylephrine infusion enhanced contractile responses to parasympathetic stimulation.
Reverse transcription‐polymerase chain reaction revealed α1D‐adrenoceptor mRNA within pterygopalatine ganglia.
At 5 weeks and 14 months postsympathectomy, adrenergic facilitation was significantly less than at 2 days, whereas prazosin‐insensitive muscarinic contraction was increased.
We conclude that degeneration of sympathetic innervation is followed rapidly by adrenoceptor‐mediated prejunctional enhancement of parasympathetic nerve‐smooth muscle neurotransmission, which occurs prior to neuroeffector junction formation as determined previously by electron microscopy. Subsequently, noradrenergic enhancement is diminished as cholinergic neurotransmission becomes established.
Activation of P2X receptors for adenosine triphosphate evokes cardiorespiratory reflexes in anaesthetized rats
Authors: McQueen D. S. , Bond S. M. , Moores C. , Chessell I. , Humphrey P. P. A. , Dowd E. 
Published: September 2004

We tested the hypothesis that activation of P2X receptors associated with vagal afferent nerves can evoke a Bezold‐Jarisch (B‐J) depressor reflex in anaesthetized rats.
Injection of αβ‐methylene ATP (αβ‐MeATP; 0.6‐600 nmol i.v.) evoked a dose‐dependent B‐J reflex comprising bradycardia, hypotension and apnoea in rats anaesthetized with pentobarbitone. Apnoea was commonly preceded by hyperventilation. Bilateral vagotomy significantly reduced the bradycardia and most of the apnoeic response without affecting hyperventilation, and unmasked a vasopressor response. Hypotension and apnoea were subject to desensitization, and ATP was about 100 times less potent than αβ‐MeATP in evoking the B‐J reflex.
ED50 values for responses to αβ‐MeATP were: bradycardia 14.6 ± 3.8 nmol; apnoea 47.1 ± 8.5 nmol; hyperventilation 23.3 ± 6.0 nmol, n= 14. The ED50 for apnoea was significantly greater than that for bradycardia or hyperventilation (P < 0.05). Atropine (2.8 μmol (kg body wt)−1 i.v.) antagonized the reflex bradycardia and hypotension.
The P2 antagonists suramin (14 μmol (kg body wt)−1 i.v.) and PPADS (17 μmol (kg body wt)−1 i.v.) antagonized the bradycardic and apnoeic components of the reflex response to αβ‐MeATP, without reducing the vasopressor or hyperventilatory responses to the agonist.
Recordings from vagal afferents showed that pulmonary inflation receptors were activated by αβ‐MeATP in 62 % of units recorded (ED50 22 ± 5 nmol) and this was blocked by PPADS (17 μmol (kg body wt)−1 i.v.); unidentified vagal afferents were also activated.
αβ‐MeATP activated carotid chemoreceptor afferents (ED50 23 ± 9 nmol), an action that was unaffected by PPADS or suramin.
The results support the hypothesis that P2X receptor subtypes for ATP are associated with specific sensory nerves that form part of the homeostatic mechanism for cardiovascular and respiratory regulation and these receptors therefore have physiological, pathological and therapeutic significance.