Search PubMed⌕ Search

Biomedical subjects

N Akaike

Publications and source records attributed to N Akaike.

At least 361 records · Page 20Linked to original sources
PubMed1985

GABA activates different types of chloride-conducting receptor-ionophore complexes in a dose-dependent manner.

We report here evidence for 3 new subtypes (alpha 1, alpha 2 and beta) of type-A GABA receptor-channel complexes that conduct chloride ions. The chloride current, ICl, was isolated in the frog sensory neuron by a combination of voltage clamp and internal perfusion. Analysis of the variance of GABA-induced ICl fluctuations shows that the channel population N decreases exponentially with single-channel conductance gamma in such a way that alpha 2 less than alpha 1 less than beta for gamma and alpha 2 much greater than alpha 1 greater than beta for N, and that the population-rank plot fits Zipf's law. Various aspects of the GABA-induced ICl are understood from dose-dependent activation and inactivation of these functionally distinct receptor-channel types. The steady-state ICl is mediated by alpha 1 at low but by beta units at high GABA concentrations, and the pronounced ICl peak at intermediate and high doses reflects the desensitization of alpha 1 and alpha 2 receptors, respectively. Picrotoxin blocks alpha 1 and alpha 2 and has no effect on beta channels. Patch-clamp recordings indicate two distinct classes of GABA-gated chloride conductances that appear to correspond to the alpha 1 and beta types. The presence of these different ICl components explains why the dose-response relationship cannot be fitted well by a single Hill equation; the fitting requires a synthesis of 3 suitable Hill equations.

Animals↗
PubMed1985

Bicuculline and picrotoxin block gamma-aminobutyric acid-gated Cl- conductance by different mechanisms.

Using isolated, internally perfused bullfrog dorsal root ganglion cells we have studied the dose-response curves for gamma-aminobutyric acid (GABA) in the presence of internally or externally applied GABA antagonists. With external application of antagonists the inhibition of the GABA current by bicuculline was competitive and that by picrotoxin was noncompetitive. Picrotoxin but not bicuculline blocked when internally perfused.

Animals↗
PubMed1985

Interactions of gamma-aminobutyric acid (GABA), pentobarbital, and homopantothenic acid (HOPA) on internally perfused frog sensory neurons.

Augmentatory actions among Cl- currents (ICl) induced by gamma-aminobutyric acid (GABA), pentobarbital (PB), and homopantothenic acid (HOPA) were investigated in isolated frog sensory neurons after suppression of Na+, K+, and Ca2+ currents using a suction pipette technique which combines internal perfusion with voltage clamp. GABA-sensitive neurons responded to both PB and HOPA, and the responses behaved as a simple Cl- electrode and reversed at the Cl- equilibrium potential (ECl). The dose-response curve for GABA-induced Cl- conductance was sigmoidal with the GABA concentration producing a half-maximum response (4.2 X 10(-5) M). Both GABA and HOPA dose-response curves shifted to the left in the presence of PB, though the facilitatory action of PB on GABA- and HOPA-induced ICl was more effective in the former. There was a significant facilitatory interaction between GABA- and HOPA-induced ICl. It is concluded that HOPA affects the GABA-GABA or PB-PB receptor interactions.

Animals↗
PubMed1985

Contribution of restricted extracellular space to the inactivation of calcium current in the snail neuron.

The mechanisms underlying the inactivation of calcium current (ICa) were investigated in isolated nerve cell bodies of Helix aspersa using a suction pipette technique that allowed voltage clamp and internal perfusion at the same time. ICa was recorded after eliminating the Na and K currents by removing Na+ and K+ both in external and internal solutions, and ICa inactivation due to intracellular Ca2+ accumulation was blocked by 5-25 mM EGTA. The inactivation rates of ICa, IBa and ISr corresponded to two exponential processes. The inactivation rates of the inward currents (IMn, ICd and IZn) less than 1/5 of ICa fitted a single exponential. However, when neurons were superfused with hypertonic external solution by adding 100 mM sucrose together with internal EGTA, the steady-state inactivation of ICa, IBa and ISr was reduced, and the inactivation processes changed to a single exponential similar to that of IMn, ICd and IZn. In contrast, internal perfusion with the hypertonic solution had no effect on the inactivation of ICa, IBa and ISr. Therefore, it was concluded that the inactivation process of ICa is dependent not only on the membrane voltage and the intracellular Ca2+ accumulation as described previously, but is also affected by the rapid fall in the concentration of Ca2+ in the restricted extracellular spaces (RES) which gets enlarged by the hypertonic external solution. The same is also true for IBa and ISr.

Action Potentials↗
PubMed1985

Blockage of the sodium current in isolated single cells from rat ventricle with mexiletine and disopyramide.

The blocking effects of local anesthetics, mexiletine and disopyramide on the sodium currents (INa) of enzymatically isolated, single cells from rat ventricle were studied under voltage clamp conditions. A suction pipette technique was used for voltage clamp and internal perfusion. Potassium currents were blocked by replacing K+ with Cs+ in the internal and external solutions; calcium currents were blocked by replacing Ca2+ with Co2+ in the external solution to isolate INa. When the cells were stimulated infrequently (less than 1 Hz), both drugs produced dose-dependent depression of INa, which was correlated with one-to-one binding to sodium channel. A half-blocking concentration (KD) of 2.8 X 10(-5) M was observed for both agents. The shape of the current-voltage curve along the voltage axis remained unchanged in the presence of either drug. Both drugs shifted the inactivation curve of INa to more negative potentials. Mexiletine produced a marked use-dependent blockage of INa, whereas disopyramide did not produce significant use-dependent block under similar experimental conditions. Both drugs prolonged the recovery of INa from inactivation. The results suggested that both drugs interact with the inactivation mechanism of the sodium channels of rat myocardial cells.

Action Potentials↗
PubMed1985

gamma-Aminobutyric-acid- and pentobarbitone-gated chloride currents in internally perfused frog sensory neurones.

gamma-Aminobutyric-acid- (GABA) and pentobarbitone-induced Cl- currents (ICl) were studied in isolated frog sensory neurones after suppression of Na+, K+ and Ca2+ currents using a suction-pipette technique combining internal perfusion with voltage clamp. All GABA-sensitive neurones responded to pentobarbitone. Both GABA- and pentobarbitone-induced ICl reversed at the Cl- equilibrium potential (ECl). The dose-response curve for maxima of GABA-induced ICl was sigmoidal with a mean concentration producing a half-maximum response, Ka of 2 X 10(-5) M at a Hill coefficient of 1.8. In the presence of pentobarbitone, the GABA dose-response curve shifted to the left without affecting the saturating maximum current. At high concentrations, both GABA and pentobarbitone could also potentiate the pentobarbitone- and GABA-induced ICl respectively, while pre-treatment with one of the two markedly attenuated currents induced by the other, indicating a 'cross-desensitization'. In the presence of pentobarbitone, the augmented response was voltage dependent and this augmentation was much greater in the inward-current direction than outward. In producing ICl, pentobarbitone and its stereoisomers were potent in the order of (-) isomer greater than (+/-) racemic mixture greater than (+) isomer. A stereospecific facilitatory action of pentobarbitone on GABA responses was also found in the same order. Responses to GABA, homotaurine, taurine, beta-alanine, 5-aminovaleric acid, (+)- and (-)-gamma-amino-beta-hydroxybutyric acid and muscimol were equally enhanced by pentobarbitone, though its action on glycine-induced ICl was less effective. Picrotoxin inhibited the GABA- and pentobarbitone-induced ICl from either side of membrane, while internal application of GABA and pentobarbitone did not exert any effect. It was concluded that pentobarbitone binds to the 'barbiturate receptors' located close to the GABA receptor-Cl- channel complex, and directly affects the GABA-GABA receptor interactions rather than the ionic channels.

Action Potentials↗
PubMed1984

Effects of a new antiarrhythmic compound SUN 1165 [N-(2,6-dimethylphenyl)-8-pyrrolizidineacetamide hydrochloride] on the sodium currents in isolated single rat ventricular cells.

The effects of a new antiarrhythmic compound, SUN 1165 (which resembles lidocaine in chemical structure) on sodium currents (INa) of enzymatically isolated, single rat ventricle cells were studied under current or voltage clamp conditions. A suction pipette technique was used for current injection and internal perfusion. Potassium currents were blocked by replacing K+ with Cs+ in the internal and external solutions, and calcium current by replacing Ca2+ with Co2+ in the external solution. When cells were stimulated infrequently (less than 1 HZ), SUN 1165 decreased INa without changing the position of the current-voltage curve. The inactivation curve of INa shifted to negative potentials along the voltage axis. The drug also produced an additional use-dependent block of INa, which depended on the frequency of the voltage clamp pulse. The effects of SUN 1165 on INa resemble those of lidocaine, although the relative importance of use-dependent action versus tonic blockade differs from that of lidocaine.

Action Potentials↗
PubMed1984

Effect of extracellular pH on sodium current in isolated, single rat ventricular cells.

Effects of extracellular pH on the sodium current (INa) of single rat ventricular cells were examined under conditions of voltage clamp and internal perfusion. In this way, pHi was controlled while pHo was changed. The combined suction pipette-microelectrode method was used. The suction pipette passed current and perfused the cell's interior; the microelectrode measured membrane potential. Increasing extracellular H+ depressed INa and slowed inactivation. The current-voltage curves for INa were shifted to positive and negative potentials at low and high pHo, respectively. Similar potential shifts were observed in both the conductance voltage curve and the steady-state inactivation voltage curve (h infinity). Conduction was also depressed at low pHo. The shifts were probably due to surface charge effects, while the impaired conduction was probably due to protonation of a site in the Na channel.

Animals↗
PubMed1984

Separation of ionic currents in the somatic membrane of frog sensory neurons.

Electrical properties of isolated frog primary afferent neurons were examined by suction pipette technique, which combines internal perfusion with current or voltage clamp using a switching circuit with a single electrode. When K+ in the external and internal solutions was totally replaced with Cs+, extremely prolonged Ca spikes, lasting for 5 to 10 sec, and Na spikes, having a short plateau phase of 10 to 15 msec, were observed in Na+-free and Ca2+-free solutions, respectively. Under voltage clamp, Ca2+ current (ICa) appeared at around -30 mV and maximum peak current was elicited at about 0 mV. With increasing test pulses to the positive side, ICa became smaller and flattened but did not reverse. Increases of [Ca]o induced a hyperbolic increase of ICa and also shifted its I-V curve along the voltage axis to the more positive direction. Internal perfusion of F- blocked ICa time-dependently. The Ca channel was permeable to foreign divalent cations in the sequence of ICa greater than IBa greater than ISr much greater than IMn greater than IZn. Organic Ca-blockers equally depressed the divalent cation currents dose- and time-dependently without shifting the I-V relationships, while inorganic blockers suppressed these currents dose-dependently and the inhibition appeared much stronger in the order of IBa = ISr greater than ICa greater than IMn = IZn.

Action Potentials↗
PubMed1984

Origins of the transient anterior-posterior asymmetry in the frog lens fiber potential.

The origin of the transient asymmetry of intracellular resting potentials between the anterior and posterior lens fibers was investigated in the isolated American bullfrog lens by a conventional microelectrode technique. In high K+, Rb+, Cs+, or NH+4 test solution applied only to the lens anterior or posterior side, anterior fibers depolarized at a slower rate than posterior ones. After a long exposure, however, the transient potential difference disappeared. The magnitude of the depolarizations of the lens fibers was in the order of K+ greater than Rb+ greater than Cs+ greater than NH+4. The resting potentials plotted as a function of external K+ concentrations ([K]0) were in agreement with Nernst equation predictions with a slope of 58 mV/decade ion concentration change. A small Na+ permeability is unmasked at a [K]0 less than 10 mM. It was concluded that the transient difference measured in potentials of anterior and posterior lens fibers on increasing external K+, Rb+, Cs+ or NH+4 depends on the anterior epithelial cell layer, which is a diffusional barrier for ions penetrating into the lens interior.

Animals↗
PubMed1984

Comparison of the intracellular membrane potentials in crystalline lenses of various frogs.

The intracellular membrane potentials were measured in the individual lens fibers of three kinds of frogs (Rana catesbeiana, Rana pipiens japonica, Rana nigromata) by a conventional glass microelectrode technique, in which the electrode was advanced to a depth of 200 micron from the anterior surface into the lens interior. The maximum intracellular membrane potentials obtained in both anterior and posterior sides of all preparations were between -90 and -95 mV. The measured potentials were nearly close to the EK, and the membrane potentials in in vitro experiments correlated well with in vivo measurements. Low membrane potentials reported previously in various frog lenses were discussed in comparison with the present results.

Animals↗
PubMed1984

Reconsideration of the indirect measurements of intracellular Na and K concentrations in the rat skeletal muscles.

The intracellular Na and K concentrations ([Na]i, [K]i) of extensor digitrum longus (EDL) and soleus (SOL) muscles of 3- to 52-week-old rats were estimated flame-photometrically. The extracellular space of 3-week-old rat muscles was significantly greater than that of 15-week-old rat muscles. The [K]i of the both muscles decreased gradually with age while [Na]i remained nearly constant. EDL had higher [K]i and lower [Na]i than SOL and the sum of the concentrations of [K]i and [Na]i was significantly greater in EDL than in SOL throughout the age period tested. Significant measurement errors were found in muscles from the youngest age group, where samples weighed less than 50 mg. A method for calculation of corrected [Na]i and [K]i values is discussed.

Aging↗
PubMed1984

Internal perfusion studies demonstrating GABA-induced chloride responses in frog primary afferent neurons.

Cl- current in gamma-aminobutyric acid (GABA)-sensitive neurons of the frog dorsal root ganglia was separated from other ionic components (i.e., Na+, Ca2+, and K+ currents) using a suction pipette technique, which allowed internal perfusion and current clamp. The GABA-induced depolarization response increased slightly on substituting Na+ by tris(hydroxymethyl)amino-methane+ or Ca2+ by Mg2+ in the external solution. Additional replacement of external and internal K+ with Cs+ further enhanced the GABA response. The GABA response was virtually unaffected when the internal perfusate contained, in addition to 60 mM Cl-, large organic anions such as isethionate-, aspartate-, and citrate- (each 70 mM) as well as aspartate- and GABA (each 35 mM). The reversal potential of GABA-induced Cl- response (EGABA) was equal to Cl- equilibrium potential (ECl) and behaved as a simple Cl- electrode following changes of external and internal Cl- concentrations. These observations indicate the adequacy of internal perfusion. The GABA-induced Cl- response increased in a sigmoidal dose-dependent manner, in which the threshold GABA concentration was around 10(-7) M and the GABA response reached ECl at 10(-4) M. When GABA concentration was higher than 6 X 10(-6) M, the responses were always accompanied by a rapid desensitization.

Animals↗
PubMed1984

[Chloride channel].

Cl- current in GABA-sensitive neurons of the frog dorsal root ganglia was separated from other Na+, Ca2+ and K+ currents using the suction pipette technique which allows internal perfusion and current clamp. Adequacy of the internal perfusion technique was assessed from the reversal potential for GABA-induced Cl- current (EGABA) at various intracellular Cl- concentrations. EGABA was equal to the Cl- equilibrium potential (ECl) and behaved as a simple Cl- electrode following changes of external and internal Cl- concentrations [(Cl]0 and [Cl]i. EGABA changed by 58 mV for a tenfold change in either [Cl]0 or [Cl]i at constant [Cl]0 or [Cl]i, respectively. GABA-induced Cl- conductance increased dose-dependently. In addition, single Cl- channel current (icl) and conductance (gamma Cl) were estimated from the Cl- current fluctuation by using both power spectrum and amplitude histogram methods, and the theoretical values were compared with those measured directly by a conventional inside-out patch clamp technique.

Animals↗
PubMed1984

Permeability to various cations of the voltage-dependent sodium channel of rat single heart cells.

The permeability to various cations of the voltage-dependent sodium channel of rat single heart cells has been studied under the current or voltage clamp conditions. The cells, dispersed by collagenase treatment, were perfused internally using a suction pipette technique. The permeability sequence, estimated from the effects of various cations on the maximum rate of rise of action potential or from either the peak amplitude or the reversal potential of the inward current was Na+ greater than Li+ greater than hydrazine greater than guanidine greater than formamidine greater than hydroxylamine greater than methylguanidine greater than monomethylamine. The ionic permeability of a compound was markedly diminished by methylation. All inorganic and organic cation currents were reduced in the presence of tetrodotoxin, a specific Na+ channel blocker. It would appear that the ionic selectivity of the sodium channel of rat single heart cells is similar to the selectivity in the squid axon and of that in the myelinated nerve of the frog.

Action Potentials↗
PubMed1983

Voltage-dependent activation of potassium current in Helix neurones by endogenous cellular calcium.

1. The effect of endogenous Ca on potential-dependent K current IKD, was examined in identifiable neurones of Helix aspersa. The suction pipette method of internal perfusion was used along with a combined voltage-clamp method in which the membrane potential was measured by a separate glass micro-electrode and the current was passed by the suction pipette. Activation of the potential-dependent A current, IA, was prevented by using holding potentials of -40 mV where IA is inactivated and by the addition of the A-current blocker 4-aminopyridine. Activation of K currents by transmembrane Ca current, IKCa, was suppressed by Co substitution for Ca ion extracellularly. 2. Under these conditions, IKD rose to a peak value and then subsided to a steady level. The current-voltage (I-V) relationship for peak IKD had an upward bump at about +50 mV that gave it an S-shape. The I-V curve for steady IKD rose continuously. Peak and steady IKD were reduced by perfusing with EGTA or F ions intracellularly. The EGTA effect occurred at intracellular Ca activity levels below 10(-7) M. Increases in the concentration of EGTAi at constant Cai had no additional effect; however, recovery experiments do not allow us to rule out some direct action of EGTA on IKD. 3. Prolonged extracellular perfusion with Co-substituted solutions also reduced IKD and the effects occurred more quickly when the solutions were made hypertonic or caffeine was added to them. The peak transient was abolished, and the small remaining steady IKD (about 5-10% of normal peak IKD) was blocked by tetraethylammonium. IKD could be restored by the temporary reintroduction of Ca in the extracellular solution. 4. The S-shape of the peak I-V relationship for IKD may be due to Ca released from an endogenous site by membrane depolarization. The reduction of steady and peak IKD to very low values by Ca chelators or prolonged perfusion with Ca-free solutions indicates that Cai is important for activation of these K channels. 5. Three cellular structures were identified in electron micrographs of freeze-fractured neurones that could be involved in potential-dependent endogenous Ca release. These were a restricted extracellularly space, an intracellular membrane system of endoplasmic reticulum that may be fused to the internal face of the plasma membrane (the subsurface cisterns of Henkart & Nelson, 1979), and intracellular vesicles that also may be fused to the plasma membrane.

Animals↗
PubMed1983

Neural regulation on the active sodium-potassium transport in hypokalaemic rat skeletal muscles.

C.N.S.-induced suppression of muscle Na-pump activity was studied in fast 'twitch' muscle, extensor digitorum longus, of hypokalaemic rats which were fed a K-deficient diet for 0-9 weeks. The results were compared with those of slow 'tonic' muscle, soleus, reported previously. K-deficient diet caused blood hypokalaemia and a considerable K+ loss and Na+ accumulation in the skeletal, heart and smooth muscles. The cellular K+ loss was in the order of soleus greater than extensor digitorum longus greater than diaphragm greater than duodenum greater than auricle greater than ventricle; C.N.S. organs such as cerebrum, cerebellum, medulla oblongata, spinal cord and liver were spared this K+ fall. Skeletal, heart and smooth muscles lost more K+ with prolongation of hypokalaemic periods, whereas plasma K+ concentration did not fall much below 1.6 mM during hypokalaemia. Peripheral nerve section, cervical and brain-stem transection, decerebration and cortical spreading depression with 20% KCl, which activated the active Na+ and K+ transport in soleus muscles during hypokalaemia, could not enhance the pump activity in extensor digitorum longus muscles. Alpha-adrenoreceptor antagonists such as phenoxybenzamine, phentolamine and dibenamine and a specific blocker of post-synaptic alpha 1-adrenoreceptor, prazosin, did not stimulate Na+ and K+ transport in the extensor digitorum longus muscles during hypokalaemia while the beta-adrenoreceptor antagonist, propranolol, also had no effect. The sensitivity of the active Na+ and K+ transport system in rat muscles to ouabain applied intraperitoneally was greater in extensor digitorum longus muscles than in soleus muscles. The binding experiment with a radiolabelled ligand of alpha 1 adrenoreceptor antagonist, [3H]prazosin, demonstrated the presence of alpha 1-adrenergic receptors on the soleus muscle membranes of hypokalaemic rats, but not of normal rats. alpha 1 Adrenergic receptors were not detected on the extensor digitorum longus muscle membranes prepared from either hypokalaemic or normal rats. The correlation between the C.N.S.-induced inhibition on the Na pump in soleus muscle during hypokalaemia and the occurrence of alpha 1 adrenergic receptors on the muscle was discussed.

Adrenergic alpha-Antagonists↗