Biomedical subjects

N Akaike

Publications and source records attributed to N Akaike.

At least 181 records · Page 10Linked to original sources

PubMed1993

Rolipram enhances the development of voltage-dependent Ca2+ current and serotonin-induced current in rat pheochromocytoma cells.

The effects of chronic treatment (6-8 days) with a phosphodiesterase inhibitor, rolipram, on the expression of voltage-dependent Ca2+ channels, nicotinic acetylcholine (ACh) receptors and 5-hydroxytryptamine (5-HT) receptors were investigated in PC12 cells. The results were compared with the effects of nerve growth factor (NGF), 8-bromo-cyclic AMP (8-Br-cAMP) and phorbol 12-myristate 13-acetate (PMA). In the morphological study rolipram, at a high concentration (100 microM) induced the extension of neurites. A similar result was obtained in 8-Br-cAMP (1 mM)-treated cells. Rolipram, at a low concentration (10 microM) or PMA (10(-7) M) did not induce obvious morphological change. NGF (100 ng/ml) induced the extension of long neurites and the formation of neural networks. Rolipram (100 microM) increased the current density (pA/pF) of voltage dependent Ca2+ current (ICa). Both NGF and 8-Br-cAMP also increased the current density of ICa, whereas PMA did not. NGF increased the current density of the nicotinic ACh response whereas rolipram, 8-Br-cAMP and PMA decreased. Rolipram (100 microM), NGF (100 ng/ml), and 8-Br-cAMP (1 mM) increased the current density of the 5-HT response whereas the effect of PMA (100 nM) was slight. The results suggest that rolipram is able to contribute to the neuronal development by increasing intracellular cAMP as well as 8-Br-cAMP. Consequently, rolipram behaves like a neurotrophic factor in cultured PC12 cells.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1993

Effect of KB-2796, a new diphenylpiperazine Ca2+ antagonist, on voltage-dependent Ca2+ currents and oxidative metabolism in dissociated mammalian CNS neurons.

The effects of KB-2796, 1-[bis(4-fluorophenyl)methyl]-4-(2,3,4- trimethoxybenzyl)piperazine-2HCl, on the low- and high-voltage activated Ca2+ currents (LVA and HVA ICa, respectively) and on oxidative metabolism were studied in neurons freshly dissociated from rat brain. KB-2796 reduced the peak amplitude of LVA ICa in a concentration-dependent manner with a threshold concentration of 10(-7) M when the LVA ICa was elicited every 30 s in the external solution with 10 mM Ca2+. The concentration for half-maximum inhibition (IC50) was 1.9 x 10(-6) M. At 10(-5) M or more of KB-2796, a complete suppression of the LVA ICa was observed in the majority of neurons tested. There was no apparent effect on the current-voltage (I-V) relationship and the current kinetics. KB-2796 delayed the reactivation and enhanced the inactivation of the Ca2+ channel for LVA ICa voltage- and time-dependently, suggesting that KB-2796 preferentially binds to the inactivated Ca2+ channel. KB-2796 at a concentration of 3.0 x 10(-6) M also decreased the peak amplitude of the HVA ICa without shifting the I-V relationship. In addition, KB-2796 reduced the oxidative metabolism (the formation of reactive oxygen species) of the neuron in a concentration-dependent manner with a threshold concentration of 3 x 10(-6) M. It is suggested that the inhibitory action of KB-2796 on the neuronal Ca2+ influx and the oxidative metabolism, in combination with a cerebral vasodilatory action, may reduce ischemic brain damage.

Animals↗

PubMed1993

Heterogeneous distribution and developmental change of metabotropic glutamate receptors in rat hippocampal CA1 pyramidal neurons.

The metabotropic glutamate (mGlu) response in dissociated rat hippocampal CA1 pyramidal neurons was recorded, using the nystatin-perforated patch-clamp technique. The mGlu response was localized in the ventral site of the hippocampal CA1 region. In both the ventral and dorsal sites of the CA1 region, the current amplitude of the mGlu responses as well as their induction probability (responsiveness) were reduced with development of the brain.

Animals↗

PubMed1993

Suppression of taurine response in acutely dissociated substantia nigra neurons by intracellular cyclic AMP.

The modulatory effect of intracellular cyclic AMP on the taurine response was investigated in acutely dissociated rat substantia nigra neurons in patch clamp configurations. Taurine acts mainly on the glycine receptor. An intracellular application of cyclic AMP (5 x 10(-4) M) inhibited the response to a high concentration of taurine (10(-3) M) by about 50%, but did not affect the response to a low concentration of taurine (10(-4) M). This inhibition was blocked somewhat by N-(2-[methylamino]ethyl)-5-isoquinolinesulfonamide (H-8) (10(-6) M), suggesting that the inhibition of taurine response might be partly mediated by an activation of protein kinase A.

Animals↗

PubMed1993

Calcium currents in pyramidal neurons acutely dissociated from the rat frontal cortex: a study by the nystatin perforated patch technique.

We studied electrical and pharmacological properties of voltage-activated Ca2+ currents (ICa) in freshly dissociated rat frontal cortical pyramidal neurons by using nystatin perforated patch and conventional patch-clamp techniques. With either nystatin perforated patch technique or conventional patch-clamp technique, low voltage-activated ICa (LVA ICa) and high voltage-activated ICa (HVA ICa) were recorded. However, in conventional whole-cell recording, HVA ICa ran down within 5-20 min, whereas the current remained stable for 50 min at least in nystatin perforated patch recording. The HVA ICa recorded by nystatin perforated patch technique was further classified to L-type, N-type and a current component resistant to both nicardipine and omega-conotoxin by their current kinetics, voltage- and drug-sensitivities. Present results suggest that the perforated patch technique is a useful method for studying the properties of high voltage-activated Ca2+ channels.

Animals↗

PubMed1993

Ammonia potentiates GABAA response in dissociated rat cortical neurons.

The ammonium ion (NH4+) evoked no response itself but facilitated the GABA-induced Cl- current (ICl) in dissociated rat cortical neurons. The GABA concentration-response curve shifted parallely to the left without changing the maximum response. Reversal potential of GABA response did not change in the presence of NH4+ at the concentration range between 0.1 and 1 mM. Ro 15-1788, a selective benzodiazepine receptor antagonist, did not affect the facilitatory action of NH4+ on GABAA receptor. The results suggest that NH4+ modifies the affinity of GABAA receptor for GABA, without the involvement of benzodiazepine receptors.

Ammonia↗

PubMed1993

Caffeine response in pyramidal neurons freshly dissociated from rat hippocampus.

The effect of caffeine on the CA1 pyramidal neurons freshly dissociated from rat hippocampus was investigated with nystatin-perforated patch technique under voltage-clamp condition. Caffeine evoked a transient outward current (Icaffeine) in a concentration-dependent manner at a holding potential of -40 mV. The activation and inactivation of Icaffeine were accelerated with increasing caffeine concentration. The reversal potential for Icaffeine was close to K+ equilibrium potential. The Icaffeine was not blocked by apamin and 4-aminopyridine but suppressed by charybdotoxin, tetraethylammonium, quinine and Ba2+. Thus, the pharmacological characteristics of Icaffeine were similar to those of Ca(2+)-activated K+ current having a large conductance (IC), which generates a fast afterhyperpolarization (a.h.p.). Icaffeine was depressed by pretreatment with a membrane-permeant Ca2+ chelator (BAPTA-AM) and by depletion of the Ca(2+)-induced Ca2+ release (CICR) pool with ryanodine. A blocker of CICR sites, procaine, potently depressed the Icaffeine. In the absence of the extracellular Ca2+, an application of 10 mM caffeine depleted the caffeine-sensitive Ca2+ pools. Icaffeine recovered in an exponential fashion in the presence of the extracellular Ca2+. It was concluded that rat hippocampal pyramidal neurons have a caffeine-sensitive Ca2+ pool. Furthermore, the Ca2+ released from the pool evokes K+ current similar to IC current and hyperpolarizes the neurons.

4-Aminopyridine↗

PubMed1993

Intracellular mechanisms of cytoplasmic Ca2+ oscillation in rat megakaryocyte.

Extracellular application of ATP and ADP evoked the oscillatory K+ currents (IKCa) resulting from the periodic rise in cytoplasmic Ca2+ concentration ([Ca2+]i) of megakaryocyte isolated from rat bone marrow (Uneyama, H., Uneyama, C., and Akaike, N. (1992) Jpn. J. Pharmacol. 58, 231). The intracellular mechanism of ATP-induced cytoplasmic Ca2+ oscillation was investigated by the use of nystatin-perforated patch-clamp technique. Caffeine and ryanodine, which release Ca2+ from the Ca(2+)-induced Ca2+ release pool (CICR), and procaine, a blocker of Ca2+ release from CICR, had no effect on the IKCa oscillation in megakaryocyte. Thapsigargin and A23187 activated IKCa irreversibly by mobilizing Ca2+, but under Ca(2+)-free conditions they activated IKCa transiently. Intracellular application of inositol 1,4,5-triphosphate (IP3) also induced IKCa oscillation. Phorbol myristate acetate (PMA), a strong activator of protein kinase C (PKC), inhibited the oscillation completely. The inhibitory action of PMA was reversed by an inhibitor of PKC, staurosporin. The oscillation of ATP-induced IKCa was disrupted by staurosporin or calmodulin (CaM) antagonists such as W-7 and trifluoperazine, resulting in a transient and successive plateau-like IKCa. These results suggest that Ca2+ oscillation in megakaryocyte is caused by the interaction of both the Ca2+ release from IP3-sensitive Ca2+ pool and the Ca2+ uptake stimulated by PKC and Ca2+/CaM complex. Furthermore, forskolin, an activator of adenylate cyclase, and isobutylmethylxanthin, an inhibitor of phosphodiesterase, inhibited the frequency, latency, and current amplitude of the oscillation in a concentration-dependent manner. These reagents inhibited IP3-induced oscillation as well as an ATP-induced oscillation. Thus, the ATP-induced [Ca2+]i oscillation of rat megakaryocyte is also modulated by cAMP.

1-Methyl-3-isobutylxanthine↗

PubMed1993

Nicotinic acetylcholine receptor in dissociated rat nucleus tractus solitarii neurons.

The ACh-activated response of the acutely dissociated neuron from the rat nucleus tractus solitarii (NTS) was investigated using conventional and perforated-patch techniques. In the present preparation, ACh and nicotine evoked inward transient currents in approximately 30% of NTS neurons tested. The ACh-activated inward current reversed the direction near 0 mV and was inhibited by D-tubocurarine in a dose-dependent manner. In contrast, muscarine resulted in no detectable changes in the NTS neurons. Some populations of the NTS had nicotinic but no muscarinic acetylcholine receptors.

Acetylcholine↗

PubMed1993

Antagonism of various tonic convulsions in mice by dextrorphan and dizocilpine.

To define their efficacy and mechanism of action, the possible antagonistic effects of intravenously administered dextrorphan and dizocilpine, non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonists, on tonic convulsions and death in a variety of experimental mice models were compared. Dextrorphan not only produced dose-dependent protection against the tonic convulsions caused by an intracerebroventricular injection of NMDA, but also showed a broad spectrum of anticonvulsant activities against tonic convulsions caused by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), kainic acid (KA), bicuculline, pentylenetetrazole or electroconvulsive shock. The anticonvulsant action of dizocilpine was found to be more efficacious for any type of tonic convulsions and was 20- to 70-fold more potent than that of dextrorphan. Dizocilpine, unlike dextrorphan, impaired motor function at doses showing its anticonvulsant activity. Bay k-8644 (a Ca2+ channel agonist)-induced seizures were not antagonized by dextrorphan. Dextrorphan and dizocilpine were characteristically selective for protective functions against death, especially with three subtypes of glutamate receptors, as death caused by NMDA but not by AMPA and KA was selectively and markedly inhibited by both dextrorphan and dizocilpine. In view of these results, the efficacy of dextrorphan and dizocilpine as antagonists of convulsant effects appears to be consistent with the interpretation that a variety of convulsants cause tonic convulsions via direct or indirect interaction with the NMDA receptor complex. Furthermore, it is suggested that influx of Ca(2+) and intracellular Ca(2+) activity, such as the Bay k-8644-modulated activation of Ca(2+) binding proteins, are not directly modified by the administration of dextrorphan, itself.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1993

Dextrorphan attenuates the behavioral consequences of ischemia and the biochemical consequences of anoxia: possible role of N-methyl-d-aspartate receptor antagonism and ATP replenishing action in its cerebroprotecting profile.

The acute anti-ischemic and anti-anoxic effects of dextrorphan (DX) were compared with those of dizocilpine (MK-801) in a variety of animal models, and in vivo and in vitro testings under anoxic conditions. DX reduced the incidence of death in ischemic mice and improved the rotarod performance of mice with brain ischemia. The ischemically-impaired memory of mice treated with DX markedly improved, as shown in the step-through type passive avoidance test, Morris water maze and in the habituation of exploratory behavior test. MK-801 likewise improved the water maze performance of the ischemically-impaired mice, but to a lesser extent. The step-through type passive avoidance performance of ischemic mice was not improved by MK-801. In the passive avoidance task with normal mice, DX, like MK-801, produced anterograde amnesia at doses higher than those needed to attenuate the behavioral effects of ischemia. DX, intravenously or centrally administered, markedly and dose-dependently reduced the incidence of death in mice receiving potassium cyanide (KCN). DX lessened the reduction in adenosine triphosphate (ATP) and increased lactate contents in mice dosed with KCN and also lessened the reduction in ATP in the TCA cycle and oxidative phosphorylation reactions caused by KCN (0.58 mmol/l), whereas MK-801 failed to show any effect on ATP formation pathways in vivo and in vitro, and failed to protect mice against KCN-induced lethal toxicity in vivo. In the in vitro studies, DX increased the adenylate kinase activity of the rat brain homogenate. DX was found to be a cerebroprotectant with anti-ischemic and anti-anoxic actions, the effects probably stemming from its N-methyl-d-aspartate receptor antagonistic property in cooperation with its ATP replenishing action.

Adenosine Triphosphate↗

PubMed1993

Time-dependent expression of Na and Ca channels in PC12 cells by nerve growth factor and cAMP.

Changes in voltage-dependent Na+ (INa) and Ca2+ currents (ICa) were investigated in PC12 cells cultured without or with either nerve growth factor (NGF) or 8-Br-cAMP for 10 days. Current recordings were made in the whole-cell mode by using the conventional patch-clamp technique under voltage-clamp conditions. Membrane capacitance, an indicator of the total cell surface area, was increased 3- and 1.5-fold by 10-day treatment with NGF and 8-Br-cAMP, respectively. At the same time, NGF increased the current density of both INa and ICa approximately 25 and 2.5 times greater than in their respective controls. 8-Br-cAMP also increased both current densities; the effect on the INa was one-third less than that of NGF, while the effect on the ICa was similar to that of NGF. It was concluded that NGF has strong and moderate effects, respectively, on the expression of voltage-dependent Na+ and Ca2+ channels. 8-Br-cAMP mimicked the effect of NGF especially in Ca2+ channel expression.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1993

Spontaneous synaptic transmission in dissociated Meynert neurons with the attached synaptic boutons.

1. Neurons acutely dissociated from the nucleus basalis of Meynert of adult rats showed spontaneous currents with rapid onset and slow decay under the whole-cell patch-clamp recording. 2. The current had the reversal potential close to the theoretical Cl- equilibrium potential (ECl) and was suppressed by 2 x 10(-6) M bicuculline and 3 x 10(-6) M strychnine. 3. The spontaneous current was suppressed reversibly in the Ca(2+)-free solution containing either EGTA or BAPTA (5 mM). The enhancement of the frequency and amplitude of the current was observed with elevated extracellular K+ concentration, which was also suppressed in the presence of the Ca(2+)-free solution. 4. Nicardipine, a blocker of voltage-dependent Ca2+ channels, had an inhibitory effect as well. 5. A selective GABAB agonist, baclofen, blocked the spontaneous current, whereas a selective antagonist, phaclofen, potently enhanced the current. 6. It is concluded that the observed spontaneous current was a spontaneous inhibitory postsynaptic current (IPSC) due to the release of GABA from the attached synaptic boutons. The release was suppressed by a GABAB receptor activation, indicating that the GABAB receptor regulates the release of GABA from nerve terminals and acts as a negative autoreceptor.

Animals↗

PubMed1993

Protein kinase A-mediated phosphorylation reduces only the fast desensitizing glycine current in acutely dissociated ventromedial hypothalamic neurons.

Modulation of glycine receptor-ionophore complex by internally perfused cyclic AMP was investigated and compared to that of GABA in the acutely dissociated ventromedial hypothalamic neurons using whole-cell and outside-out patch-clamp techniques. Cyclic AMP significantly reduced both GABA- and glycine-gated chloride currents. The reduction in glycine-induced chloride current was specific in that only the fast-desensitizing one gated by high concentrations of glycine (30-100 microM) was affected. Cyclic AMP did not modulate the non-desensitizing current induced by lower concentrations (6-10 microM). Addition of N-[-2-(methylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride, a protein kinase A inhibitor, did not have a significant effect on its own but prevented the attenuation of fast desensitizing glycine current induced by cyclic AMP. Both the reversal potential and inactivation kinetics of glycine current were not affected by the activation of protein kinase A, suggesting that cyclic AMP-mediated attenuation is not due to an enhancement of desensitization. In outside-out patch studies intracellular perfusion of cyclic AMP reduced the open probability of the 100 microM glycine-activated channels without affecting that of the 6 microM glycine-activated channels. In conclusion, cyclic AMP selectively modulates the channel open frequency of the glycine receptor when activated at higher concentrations through a protein kinase A-mediated phosphorylation.

Animals↗

PubMed1993

Antiarrhythmic agents act differently on the activation phase of the ACh-response in guinea-pig atrial myocytes.

1. Anti-acetylcholine effects of pilsicainide, flecainide, disopyramide and propafenone on the acetylcholine (ACh)-induced K+ current (IK.ACh) were examined in dissociated guinea-pig atrial myocytes under whole-cell voltage clamp by the use of the 'concentration-clamp' technique. 2. The IK.ACh was activated with a latency of about 100 ms after 1 microM ACh application and desensitized to a steady-state level. The latent period and the time to peak response were shortened with increasing ACh concentration. 3. The values of half-maximal inhibition (IC50) on the peak and steady state responses were 25 and 25 microM for pilsicainide, 1.7 and 2.0 microM for disopyramide, 19 and 2.0 microM for flecainide and 0.7 and 0.2 microM for propafenone, respectively. 4. Pilsicainide and disopyramide increased the latent period and the time to peak of IK.ACh in a concentration-dependent manner. Flecainide and propafenone did not change the latent period, but shortened the time to peak and hastened the decay of IK.ACh in a voltage-independent manner. 5. The results suggest that the mechanisms underlying the anti-acetylcholine effect of antiarrhythmic drugs are different among these drugs: i.e., pilsicainide and disopyramide mainly block the muscarinic ACh receptors while flecainide and propafenone inhibit the K+ channel itself as open channel blockers.

Acetylcholine↗

PubMed1993

Caffeine and related compounds block inhibitory amino acid-gated Cl- currents in freshly dissociated rat hippocampal neurones.

1. The effects of caffeine and related compounds on responses mediated by inhibitory amino acids were investigated in freshly dissociated rat hippocampal pyramidal neurones by conventional and nystatin perforated patch-clamp techniques. 2. Glycine and gamma-aminobutyric acid (GABA) evoked Cl- currents in hippocampal neurones. The half-maximum effective concentrations (EC50) of glycine and GABA were 8.5 x 10(-5) and 5 x 10(-6) M, respectively. 3. Caffeine reversibly inhibited both 10(-4) M glycine- and 10(-5) M GABA-induced Cl-currents in a concentration-dependent manner. The half-maximum inhibitory concentrations (IC50) of caffeine were 4.5 x 10(-4) M for the glycine response and 3.6 x 10(-3) M for the GABA response. 4. Caffeine shifted the concentration-response curve of IGly to the right without affecting the maximum response. 5. The inhibitory action of caffeine did not show voltage-dependency. 6. The blocking action of caffeine was not affected by intracellular perfusion with 5 mM BAPTA or by pretreatment with the protein kinase A inhibitor, H-8. This excludes the participation of Ca2+ or cyclic AMP in the inhibitory action of caffeine. 7. Caffeine failed to inhibit the augmentations of aspartate- and N-methyl-D-aspartate (NMDA) -gated current by glycine, suggesting that caffeine has no effect on the allosteric glycine binding site on the NMDA receptor. 8. The inhibitory effects of some xanthine derivatives on IGly were compared. The inhibitory potency of those compounds on IGly was in the order of pentoxifylline > theophylline > or = caffeine > paraxanthine > IBMX > or = theobromine > dyphylline. Xanthine had no effect. 9. The results indicate that methylxanthines including caffeine may act directly on the glycine receptor Cl- channel complex in rat hippocampal pyramidal neurones. The blockade of the inhibitory amino acid response by methylxanthines may be involved in the excitatory side effects of methylxanthines in the mammalian central nervous system.

Amino Acids↗

PubMed1993

Differential properties of type I and type II benzodiazepine receptors in mammalian CNS neurones.

1. The effects of benzodiazepine receptor (BZR) partial agonists, Y-23684 and CL218,872, were compared with its full agonist, diazepam, on gamma-aminobutyric acid (GABA)-induced Cl- current (ICl) in acutely dissociated rat cerebral cortex (CTX), cerebellar Purkinje (CPJ) and spinal ventral horn (SVH) neurones, by the whole-cell mode patch-clamp technique. 2. The GABA-induced responses were essentially the same in both SVH and CPJ neurones, but the KD value of the GABA response in CTX neurone was lower than those in the other two brain regions. 3. Enhancement of the GABA response by the two partial agonists was about one-third of that by diazepam in the SVH neurones (where type II subtype of BZR, BZ2, is predominant), whereas these partial agonists potentiated the GABA response as much as diazepam in CPJ neurones (where the type I subtype of BZR, BZ1, is predominant). In CTX neurones where both type I and II variants are expressed, the augmentation ratio of the GABA response by diazepam was between the values in CPJ and SVH neurones. 4. In concentration-response relationships of BZR partial agonists, the threshold concentrations, KD values and maximal augmentation ratio of the GABA response were similar in all CTX, CPJ and SVH neurones. Also, in all preparations, the threshold concentration and KD values of diazepam action were 10 fold less than those induced by partial agonists. 5. All BZR agonists shifted the concentration-response relationship for GABA to the left without changing the maximum current amplitude, indicating that activation of both BZ1 and BZ2 increase the affinity of the GABAA receptor for GABA. 6. The results are important in clarifying the mechanism of anxiety and might explain the anxioselectivity of BZR partial agonists.

Aging↗

PubMed1993

Existence of rolipram-sensitive phosphodiesterase in rat megakaryocyte.

1. The effect of rolipram (ME3176) on ADP- and IP3-induced repetitive IK(Ca) in rat megakaryocyte was investigated by use of the nystatin perforated patch and conventional whole-cell patch-clamp techniques. 2. The ADP-induced IK(Ca) was depressed by treatment with rolipram in a concentration-dependent manner. The inhibition by rolipram disappeared after treatment with a cyclic nucleotide-dependent protein kinase inhibitor, H-8. The inhibition of IK(Ca) was also observed in the presence of cyclic AMP accumulating agents such as forskolin and isobutylmethylxanthine (IBMX). 3. Rolipram enhanced the inhibitory action of forskolin, suggesting that rolipram facilitates the accumulation of cyclic AMP by blocking its breakdown. Similar results was obtained with adenosine, an endogenous adenylate cyclase activator. 4. Intracellular application of inositol trisphosphate (IP3) induced repetitive IK(Ca) in megakaryocytes. The induced IK(Ca) was also inhibited by rolipram and by other cyclic AMP accumulating agents. 5. It was concluded that megakaryocytes possess rolipram-sensitive phosphodiesterase (PDE), which was not detected in platelets, but plays a distinct modulatory role in megakaryocytes for generating ADP-induced IK(Ca).

1-Methyl-3-isobutylxanthine↗