Biomedical subjects

H Hazama

Publications and source records attributed to H Hazama.

At least 37 records · Page 2Linked to original sources

PubMed1997

Effects of extracellular pH on receptor-mediated Ca2+ influx in A7r5 rat smooth muscle cells: involvement of two different types of channel.

1. The effects of extracellular pH (pHo) on receptor (vasopressin or endothelin-1)-mediated Ca2- entry and Ca(2+)-permeable channels were investigated in aortic smooth muscle cells (A7r5) from rat embryonic thoracic aorta. Intracellular Ca2+ ([Ca2+]i) was measured using fura-2 AM and whole-cell voltage clamp techniques were employed. 2. Vasopressin and endothelin-1 (100 nM) in the presence of nicardipine (10 microM) evoked a sustained rise in [Ca2+]i due to calcium entry. Extracellular acidosis decreased receptor (vasopressin or endothelin-1)-mediated Ca2+ entry, while extracellular alkalosis potentiated it. 3. Depletion of intracellular Ca2+ stores with thapsigargin (1 microM) also evoked Ca2+ entry activated by emptying of intracellular Ca2+ stores (capacitative Ca2+ entry). Extracellular acidosis decreased this capacitative Ca2+ entry, while extracellular alkalosis potentiated it. 4. Under voltage-clamp conditions with Ca+ internal solution, vasopressin and endothelin-1 activated non-selective cation currents (ICAT). Ba2+ or Ca2+ were also charge carriers of ICAT. Reducing the pHo inhibited ICAT, while increasing pHo potentiated it in a reversible manner. 5. Intracellular pH (pHi) changes did not cause the same marked effects as pHo changes, and a high concentration of Hepes (50 mM) in the patch pipette did not inhibit the effects of pHo on ICAT. 6. Similar results were obtained when ICAT was activated by GTP gamma S (1 mM) applied through the patch pipette, even in the absence of agonists, probably because of direct activation of GTP-binding proteins coupled to the receptors. 7. In cells treated with thapsigargin, addition of Ca2+ to the bath solution induced Ca(2+)-dependent K+ currents activated by capacitative Ca2+ entry. However, no measurable ionic currents activated by capacitative Ca2+ entry (ICRAC) were observed under conditions with Cs+ internal solution and EGTA (5 mM), although vasopressin still activated ICAT. 8. These results suggest that the contractile agonists vasopressin and endothelin-1 evoked Ca2+ entry through two different types of Ca(2+)-permeable channel (ICAT and ICRAC) and pHo affects these channels, which may modulate receptor-mediated Ca2+ influx in A7r5 cells. Thus, pH-induced changes of these channels may play a pathophysiological role in the control of receptor-mediated contractions.

Animals↗

PubMed1997

Effect of caffeine on mucus secretion and agonist-dependent Ca2+ mobilization in human gastric mucus secreting cells.

Caffeine is known to stimulate gastric acid secretion, but, the effects of caffeine on gastric mucus secretion have not been clarified. To elucidate the action of caffeine on gastric mucin-producing cells and its underlying mechanism, the effects of caffeine on mucus glycoprotein secretion and agonist-induced [Ca2+]i mobilization were examined in human gastric mucin secreting cells (JR-I cells). The measurement of [Ca2+]i using Indo-1 and the whole cell voltage clamp technique were applied. Mucus glycoprotein secretion was assessed by release of [3H]glucosamine. Caffeine by itself failed to increase [Ca2+]i and affect membrane currents, while it dose-dependently inhibited agonist (acetylcholine (ACh) or histamine)-induced [Ca2+]i rise, resulting in inhibiting activation of Ca2+-dependent K+ current (I(K.Ca)) evoked by agonists. The effect of caffeine was reversible, and the half maximal inhibitory concentration was about 0.5 mM. But, caffeine did not suppress [Ca2+]i rise and activation of I(K.Ca) induced by A23187 or inositol trisphosphate (IP3). Theophylline or 3-isobutyl-1-methyl-xanthine (IBMX) did not mimic the effect of caffeine. Caffeine failed to stimulate mucus secretion, while it significantly decreased ACh-induced mucus secretion. These results indicate that caffeine selectively inhibits agonist-mediated [Ca2+]i rise in human gastric epithelial cells, probably through the blockade of receptor-IP3 signaling pathway, which may affect the mucin secretion.

Caffeine↗

PubMed1997

Extracellular Mg2+ inhibits receptor-mediated Ca(2+)-permeable non-selective cation currents in aortic smooth muscle cells.

The effects of extracellular Mg2+ on receptor-mediated Ca(2+)-permeable non-selective cation currents were investigated in a cultured aortic smooth muscle cell line (A7r5) from rat thoracic aorta, using the whole-cell voltage-clamp technique. Under the Cs(+)-containing internal solution, both vasopressin and endothelin-1 (100 nM) activated a long-lasting inward current with a high noise level. The reversal potential of these agonists-induced current was approximately +0 mV, and was not significantly altered by the replacement of [Cl-]i or [Cl-]o, suggesting that the inward current was a cation-selective channel. La3+ and Cd2+ (1 mM) almost completely abolished the vasopressin or endothelin-induced non-selective cation current; however, nifedipine (10 microM) failed to inhibit it significantly. Extracellular Mg2+ (3-20 mM) also markedly inhibited the vasopressin- or endothelin-induced non-selective cation current in a concentration-dependent manner. When a non-hydrolysable GTP-analogue, GTP gamma S (1 mM), was applied from the patch pipette, the non-selective cation current was gradually activated even in the absence of agonist (vasopressin or endothelin-1), probably due to the direct activation of GTP-binding proteins coupled to the receptors. Extracellular Mg2+ (3-20 mM) also suppressed the activation of non-selective cation current induced by GTP gamma S, suggesting that the inhibitory sites of Mg2+ are not located on the receptors. These results suggest that extracellular Mg2+ inhibits receptor-mediated non-selective cation current, which may contribute to the relaxation effects of Mg2+ in vascular smooth muscle cells.

Animals↗

PubMed1997

Inhibitory effects of omega-3 polyunsaturated fatty acids on receptor-mediated non-selective cation currents in rat A7r5 vascular smooth muscle cells.

1. The effects of omega-3 polyunsaturated fatty acids on receptor-mediated non-selective cation current (Icat) and K+ current were investigated in aortic smooth muscle cells from foetal rat aorta (A7r5 cells). The whole-cell voltage clamp technique was employed. 2. With a K(+)-containing solution, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA, 30 microM) produced an outward current at a holding potential of -40 mV. This response was inhibited by tetraethylammonium (20 mM) or Cs+ in the patch pipette solution, and the reversal potential of the EPA-induced current followed the K+ equilibrium potential in a near Nernstian manner. 3. Under conditions with a Cs(+)-containing pipette solution, both vasopressin and endothelin-1 (100 nM) induced a long-lasting inward current at a holding potential of -60 mV. The reversal potential of these agonist-induced currents was about +0 mV, and was not significantly altered by the replacement of the extracellular or intracellular Cl+ concentration, suggesting that the induced current was a cation-selective current (Icat). 4. La3+ and Cd2+ (1 mM) completely abolished these agonist-induced Icat, but nifedipine (10 microM) failed to inhibit it significantly. 5. omega-3 polyunsaturated fatty acids (3-100 microM), EPA, DHA and docosapentaenoic acids (DPA), inhibited the agonist-induced Icat in a concentration-dependent manner. The potency of the inhibitory effect was EPA > DHA > DPA, and the half maximal inhibitory concentration (IC50) of EPA was about 7 microM. 6. Arachidonic and linoleic acids (10, 30 microM) showed a smaller inhibitory effect compared to omega-3 fatty acids. Also, oleic and stearic acids (30 microM) did not show a significant inhibitory effect on Icat. 7. A similar inhibitory action of EPA was observed when Icat was activated by intracellularly applied GTP gamma S in the absence of agonists, suggesting that the site of action of omega-3 fatty acids is not located on the receptor. 8. These results demonstrate that omega-3 polyunsaturated fatty acids can activate a K+ current and also effectively inhibit receptor-mediated non-selective cation currents in rat A7r5 vascular smooth muscle cells. Thus, the data suggest that omega-3 fatty acids may play an important role in the regulation of vascular tone.

Animals↗

PubMed1997

Thromboxane inhibition and monocrotaline-induced pulmonary hypertension in rats.

Monocrotaline (MCT)-induced pulmonary hypertension (PH) is a useful model for the investigation of this disorder in humans. The role of thrombocytes in the genesis of PH has already been addressed; however, the exact mechanism by which they induce PH remains to be elucidated. We investigated the effects of a thromboxane A2 (TXA2) synthase inhibitor (OKY-046) and a TXA2/prostaglandin H2 (PGH2) receptor antagonist (ONO-8809) on the development of MCT-induced PH. A single dose of MCT (60 mg/kg bodyweight; BW) was injected subcutaneously in Wistar rats 24 h after the administration of OKY-046 or ONO-8809. The TXA2 inhibitors were administered by gavage daily for 3 weeks. Urinary excretion of eicosanoids was determined by radioimmunoassay. At the end of the treatment period, the lungs, heart and kidneys were morphologically examined. The per cent medial thickness of the muscular pulmonary arteries (%MT) and the ratio of the right to the left ventricular mass including the septum (RV/LV + S) increased significantly in MCT-treated rats compared with the control rats. The %MT was attenuated by the administration of ONO-8809. Either OKY-046 or ONO-8809 attenuated the increase in RV/LV + S. In addition, both TXA2 inhibitors reduced urinary excretion of 11-dehydro-TXB2, particularly during the early phase of PH, suggesting that platelet aggregation was reduced. These findings suggest that the inhibition of TXA2 by synthase inhibition or receptor antagonism reduces or delays the development of MCT-induced PH in rats, probably by inhibiting platelet aggregation.

Animals↗

PubMed1996

Analysis of the mRNA cap-binding ability of human eukaryotic initiation factor-4E by use of recombinant wild-type and mutant forms.

In order to identify the amino acid residues necessary for the selective recognition of the mRNA cap structure by human eukaryotic initiation factor-4E (eIF-4E), which plays a central role in the first step of mRNA translation, we prepared recombinant wild-type and fourteen mutant forms and compared their cap-binding abilities by affinity chromatography. By the direct expression of a synthetic gene encoding human eIF-4E as the soluble form in Escherichia coli and the application on a 7-methylguanosine-5'-triphosphate-Sepharose 4B cap affinity column, pure recombinant eIF-4E was prepared; the optimum pH for the binding of the mRNA cap was 7.5. Among the amino acid residues conserved among various eIF-4E species, each of 14 functional residues was replaced with a nonpolar amino acid (alanine or leucine). All mutant eIF-4E genes, which were constructed by site-directed mutagenesis, were expressed in the same way as the wild type, and their cap-binding abilities were compared with that of the wild type. Consequently, all eight tryptophan residues. Glu103, and two histidine residues at positions 37 and 200 in human recombinant eIF-4E were suggested to be important for the recognition of the mRNA cap structure through direct interaction and/or indirect contributions. Indirect contributions included the construction of the overall protein structure, especially the cap-binding pocket.

Amino Acid Sequence↗

PubMed1996

Neurokinin A and Ca2+ current induce Ca(2+)-activated Cl(-) currents in guinea-pig tracheal myocytes.

1. Membrane currents were recorded by a patch clamp technique in guinea-pig tracheal myocytes, using the whole cell mode with Cs(+) internal solution. 2. Both neurokinin A (NKA, 1 mu M) and caffeine (10 mM) evoked Ca(2+)-activated Cl- currents (I[Cl(Ca)]) transiently. In Ca(2+)-free bathing solution, the first application of NKA or caffeine elicited I[Cl(Ca)] but the second application of these substances failed to activate it. In addition, pretreatment with ryanodine in the presence of caffeine abolished the response to both NKA and caffeine whilst heparin (200 mu g ml(-1)) only blocked the NKA-induced response. I[Cl(Ca)] was also elicited by inositol 1,4,5-trisphosphate (IP(3)). 3. Command voltage pulses positive to 0 mV from a holding potential of -60 mV activated the voltage-dependent L-type Ca2+ current (I(Ca,L)) and late outward current. Upon repolarization to the holding potential, slowly decaying inward tail currents were recorded. The outward current during the depolarizing pulses and the inward tail current were enhanced by Bay K 8644, but completely blocked by Cd2+ or nifedipine. Replacement of external Ca2+ with Ba2+, removal of Ca2+ from the bath solution, or inclusion of EGTA (5 mM) in the patch pipette, also led to abolition of these currents, indicating that they were Ca2+ dependent, and that Ca2+ influx due to I(Ca,L) activated the currents. 4. When [Cl(-)](O) or [Cl(-)](i) was changed, the reversal potential (E(rev)) of the Ca2+-activated currents shifted, thus behaving like a Cl(-)-selective ion channel as predicted by the Nernst equation. DIDS (1 mM) completely abolished the currents, also suggesting that they were I[Cl(Ca)]. 5. NKA (1 mu M) and caffeine (30 mM) transiently activated I[Cl(Ca)], and after that both agents markedly reduced I[Cl(Ca)] induced by I(Ca,L). This is probably due to sarcoplasmic reticulum (SR) Ca2+ release induced by NKA or caffeine, followed by inhibition of the Ca(2+)-induced Ca2+ release from the SR. 6. The present results indicate that I[Cl(Ca)] can be activated by SR Ca2+ release due to NKA or caffeine (through IP(3) or ryanodine receptors) as well as by Ca2+ influx due to I(Ca,L). It also suggests that activation of I[Cl(Ca)] by NKA may be mediated by the production of IP(3), which releases Ca2+ from the SR.

Action Potentials↗

PubMed1996

Endothelin-1 and vasopressin activate Ca(2+)-permeable non-selective cation channels in aortic smooth muscle cells: mechanism of receptor-mediated Ca2+ influx.

The effects of vasopressin and endothelin-1 on cultured aortic smooth muscle cell lines (A7r5) were investigated by measurements of intracellular calcium [Ca2+]i and the patch-clamp techniques. Vasopressin and endothelin-1 (100 nM) evoked an initial peak followed by a smaller sustained rise of [Ca2+]i in the presence of extracellular calcium [Ca2+]o. In the absence of [Ca2+]o, only the initial peak of [Ca2+]i was observed. Therefore, the initial peak of [Ca2+]i was mainly due to calcium release from the storage sites, whereas the later sustained rise of [Ca2+]i was due to the calcium entry from outside. The sustained rise of [Ca2+]i was unaffected by nifedipine (10 microM) significantly, but was completely abolished by La3+ (1 mM). Under current clamp conditions with K(+)-internal solution, vasopressin and endothelin-1 (100 nM) produced hyperpolarization, then followed by depolarization. Under voltage clamp conditions at a holding potential of -40 mV, both vasopressin and endothelin-1 first activated the outward current, then followed by a long-lasting inward current with a high noise level. The first outward current was abolished by charybdotoxin (100 nM), Cs+ in the patch pipette and high EGTA (10 mM) in the pipette, suggesting that it was a Ca(2+)-sensitive K+ current (IK.Ca). The inward current was still elicited with the patch pipette containing Cs(+)-internal solution, and reversed at about 0 mV. The reversal potential was not significantly altered by the replacement of [Cl-]i or [Cl-]o, proposing that the inward current is a cation selective channel (IN.S.). The inward current was also observed even when extracellular cations are Ca2+. La3+ (1 mM), Cd2+ (1 mM) completely abolished the vasopressin-induced (IN.S.), however, nifedipine (10 microM) failed to inhibit it significantly. Single channel activities were recorded in the cell-attached configurations when vasopressin or endothelin-1 was applied to the bathing solution. The unitary conductance of the channels was approximately 20 pS with 140 mM Na+, Cs+, or K+ in the pipette, but was 15 pS with 110 mM Ca2+ in the pipette. Permeabilities sequence calculated from the reversal potentials was Na+ not equal to Cs+ not equal to K+ > Ca+. These results provide evidence that calcium entry and membrane depolarization elicited by vasopressin or endothelin-1 are mediated by a receptor-mediated Ca(2+)-permeable non-selective cation channel in aortic smooth muscle cells.

Aorta, Thoracic↗

PubMed1996

Periodicity and prediction of mania onsets in biopolar I affective disorders.

In studying the periodicity of mania onsets, cycle-oriented diagrams were made of the clinical course from 257 manic episodes analyzed retrospectively in 34 bipolar I manic-depressive patients for a period of about 5 years. Using these diagrams, the frequent period of mania onsets located in one-quarter of the follow-up period was pre-estimated, and the accordance ratio during a 25 month follow-up period was analyzed. The accordance ratio in all subjects was 39% (11/28) for the first episode and 35% (7/20) for the second episode. These ratios were not significantly different from the expected level (25%). The number of subjects was limited to 11 patients (10 rapid and 1 non-rapid cyclers) whose number of episodes used for the determination of the index cycle was eight or more. The accordance ratio was 64% (7/11) and 60% (6/10) for the first and second episodes, respectively. Their levels were significantly higher than those expected. Periodicity of mania onsets existed at least in rapid cyclers with abundant past data.

Adult↗

PubMed1996

Ouabainlike compound in hypertension associated with ectopic corticotropin syndrome.

Molecular mechanisms related to sodium retention have been implicated in the pathogenesis of hypertension. It is unclear how sodium retention leads to a rise in blood pressure, but ouabainlike compound may act as a final common pathway in sodium-induced hypertension. In ectopic corticotropin syndrome, hypertension has been attributed to cortisol inactivation overload, giving rise to mineralocorticoid-type hypertension. We sequentially measured plasma and urinary levels of ouabainlike compound over 2 months to evaluate its role in the hypertensive mechanisms in a 64-year-old man with this syndrome caused by lung cancer. His data included hypokalemia and increased cortisol concentrations, corticotropin levels, and urinary 17-hydroxycorticosteroid excretion. Plasma renin activity was suppressed. Plasma and urinary levels of ouabainlike compound were markedly increased concomitantly with high blood pressure. The maximum plasma level was 40-fold the normal range of the subject. After chemotherapy, ouabainlike compound levels gradually decreased in parallel with the decline in blood pressure and rise in potassium concentration. A correlation was observed between plasma and urinary levels of ouabainlike compound (P < .05). Plasma and urinary levels of ouabainlike compound correlated with systolic (P < .01) and diastolic (P < .05) pressures, respectively. The peak of ouabainlike compound in plasma and urine coincided with that of authentic ouabain on high-performance liquid chromatography. Ouabainlike compound derived from urine inhibited [3H]ouabain binding to human erythrocytes. These findings suggest that ouabainlike compound with biological activity could partly account for hypertension in ectopic corticotropin syndrome.

ACTH Syndrome, Ectopic↗

PubMed1995

17beta-Estradiol inhibits the voltage-dependent L-type Ca2+ currents in aortic smooth muscle cells.

To elucidate the mechanisms of estrogens-induced relaxation effects on vascular smooth muscle cells, the effects of estrogens and the related hormones were examined in cultured rat thoracic aortic smooth muscle cell lines (A7r5), using the whole-cell voltage clamp technique. The patch pipette was filled with 140 mM CsCl- or KCl-containing internal solution. With CsCl-internal solution, 17beta-estradiol and synthetic estrogens, ethynylestradiol and diethylstilbestrol (0.1-30 mu M) inhibited the Ba2+ inward current (IBa) through the voltage-dependent L-type Ca2+ channel in a concentration-dependent and reversible manner. The potency of the inhibitory effects on IBa was 17beta-estradiol < ethynylestradiol < diethylstilbestrol. 17beta-Estradiol (10 mu M) appeared to reduce the maximal conductance of IBa with only a slight shift of voltage-dependency of inactivation and to affect IBa in a use-independent fashion. On the other hand, testosterone and progesterone (30 mu M) failed to affect IBa. At a holding potential of -40 mV, both vasopressin and endothelin-1 (100 nM) activated a long-lasting inward current. After endothelin-1 (100 nM) activated the current, the additional application of vasopressin (100 nM) could not induce it furthermore, suggesting that each agonist activates the same population of the channels. The reversal potential of the current was about 0 mV and was not significantly altered by replacement of [Cl-]i or [Cl-]0 and the inward current was also observed even when extracellular cations are Ca2+, proposing that it was a Ca2+-permeable non-selective cation channel (IN.S.). La3+ or Cd2+ (1 nM) completely abolished IN.S., however, nifedipine (10 mu M) failed to inhibit it at all. Diethylstilbestrol (1-30 mu M) suppressed the IN.S. evoked by both endothelin-1 and vasopressin in a concentration-dependent manner, while 17beta-estradiol, ethynylestradiol, progesterone and testosterone (30 mu M) failed to inhibit it significantly. In addition, at a holding potential of +0 mV, 17beta-estradiol by itself did not affect the holding currents, and did not inhibit K+ currents evoked by endothelin-1 or vasopressin, possibly due to the Ca2+ release from the storage sites. These results suggest that 17beta-estradiol may play a role in regulating vascular tone, selectively by inhibiting the voltage-dependent L-type Ca2+ current in vascular smooth muscle cells.

Animals↗

PubMed1995

Regional differences in transient outward current density and inhomogeneities of repolarization in rabbit right atrium.

BACKGROUND: Recent experimental and clinical studies on atrial flutter have demonstrated that the crista terminalis (CT) plays an important role in the genesis of atrial reentry. To elucidate the underlying mechanism of its role, we characterized the electrophysiological repolarization properties of CT cells by comparing them with those of the pectinate muscles (PM). METHODS AND RESULTS: After action potential properties of both regions were compared by conventional microelectrode technique in multicellular atrial tissues, the whole-cell clamp experiments were applied in atrial cells isolated from both regions. Action potential duration (APD) was more prolonged in CT than in PM in multicellular preparations (APD90 77 +/- 5 ms versus 52 +/- 8 ms at 1 Hz, P < .01), though the other properties did not differ significantly. Similarly, in isolated atrial cells, APD was more prolonged in CT cells than in PM cells (APD90 63 +/- 7 ms versus 41 +/- 6 ms at 0.1 Hz, P < .01). Isolated single cells were larger in CT than in PM. The whole-cell clamp recordings showed no definite distinctions in the density of the voltage-dependent L-type Ca2+ current and the inwardly rectifying K+ current between these cells but revealed a significant reduction of the density of the 4-aminopyridine-sensitive transient outward current (Ito) in CT cells compared with that in PM cells (6.3 +/- 0.7 pA/pF versus 10.3 +/- 0.8 pA/pF at +20 mV, P < .05). However, no differences in the kinetics or the voltage dependence of Ito were observed between the cells. The time course of recovery from inactivation of Ito was also similar in both types of cells. CONCLUSIONS: These results suggest that the preferential reduction in the density of Ito in the CT cells could contribute to prolong their APD, which may be related to the genesis of atrial reentry.

Action Potentials↗

PubMed1995

Ionic basis of neurokinin-A-induced depolarization in single smooth muscle cells isolated from guinea-pig trachea.

Neurokinin A (NKA) caused single tracheal smooth muscle cells (TSMCs) to contract. The effects of NKA on the electrical activity of guinea-pig TSMCs were examined using the tight-seal whole-cell patch-clamp technique. Under current-clamp conditions at rest, the membrane potential of TSMCs spontaneously oscillated at about -40 mV and NKA rapidly depolarized the membrane potential to nearly 0 mV, which then gradually repolarized to about -20 mV in the presence of NKA. The oscillations in potential disappeared transiently during the rapid phase of depolarization in response to NKA and reappeared during the sustained phase of depolarization. Under voltage-clamp conditions, NKA evoked an inward current which faded quickly. Subsequently, the cell conductance in the presence of NKA at potentials greater than -40 mV decreased gradually. The reversal potential of the NKA-induced inward current was about 0 mV, and shifted with changes in the Cl- equilibrium potential. The Cl- current was not elicited by NKA when using a pipette solution containing 10 mM ethylenebis(oxonitrilo)tetraacetic acid (EGTA). During the sustained phase, K+ currents evoked by depolarizing voltage steps were inhibited by NKA. The present results indicate that NKA causes rapid and sustained depolarization of TSMCs by two distinct mechanisms: (1) initial transient activation of the Ca(2+)-dependent Cl- current, and (2) sustained inhibition of K+ currents.

Animals↗

PubMed1995

Flecainide inhibits the transient outward current in atrial myocytes isolated from the rabbit heart.

We examined the effects of flecainide, a class Ic antiarrhythmic agent, on membrane currents in single rabbit atrial myocytes, using the tight-seal whole cell voltage-clamp technique. Under the current-clamp condition, flecainide (1-100 microM) prolonged the action potential duration at both the early and the late phases of repolarization in a concentration-dependent manner without affecting the resting membrane potential. In the presence of 4-aminopyridine, however, the drug affected the atrial action potential duration differently than it did in the absence of 4-aminopyridine: it shortened the early phase and only slightly lengthened the late phase of the atrial action potential. Under the voltage-clamp condition, flecainide suppressed the 4-amino-pyridine-sensitive, Ca(++)-insensitive transient outward current in a concentration-dependent fashion (the concentration for the half-maximal effect was approximately 17 microM). The drug also slightly inhibited the voltage-dependent L-type Ca++ current and delayed outward K+ current. Flecainide apparently accelerated the inactivation time course of the transient outward current but did not affect the voltage-dependence of its steady-state inactivation. These actions of flecainide on the transient outward current could be described by a voltage-dependent first-order interaction of the drug with the channel.

4-Aminopyridine↗

PubMed1994

Effects of azelastine on membrane currents in tracheal smooth muscle cells isolated from the guinea-pig.

Azelastine [4-(p-chlorobenzyl)-2-(hexahydro-1-methyl -1H-azepin-4-yl)-1-(2H)-phthalazinone hydrochloride], an anti-allergic agent, inhibited the high K(+)-induced contraction in tracheal smooth muscle cells isolated from the guinea-pig. In order to investigate the ionic mechanisms, we examined the effects of azelastine on membrane currents, using the tight-seal whole cell voltage clamp technique. Azelastine (1-100 microM) caused an inhibition of the Ba2+ inward current (IBa) through the voltage-dependent L-type Ca2+ channel in a concentration-dependent manner. The inhibitory effect of azelastine on IBa was fully reversible. The IC50 value for azelastine-induced inhibition of IBa was approximately 8 microM, and 100 microM azelastine completely suppressed IBa. Azelastine exerted mainly a tonic block of IBa but did not show use dependence. Azelastine (10 microM) shifted the quasi-steady-state inactivation curve of IBa to more negative membrane potentials by approximately -20 mV, suggesting that the inhibitory effect of azelastine on IBa was voltage-dependent. In addition, azelastine produced inhibitory actions on other membrane currents (i.e. the voltage-dependent transient outward K+ current and the Ca(2+)-activated oscillatory K+ current) at doses higher than 10 microM. These results suggest that azelastine inhibits the voltage-dependent L-type Ca2+ current in single tracheal smooth muscle cells, which may contribute to the anti-allergic actions of azelastine in airways.

Animals↗

PubMed1994

Molecular mechanism of cibenzoline-induced anticholinergic action in single atrial myocytes: comparison with effect of disopyramide.

The anticholinergic effects of cibenzoline were examined and compared with those of disopyramide in atrial myocytes isolated from guinea pig heart. The tight-seal whole-cell voltage clamp technique was performed with a patch pipette filled with guanosine-5'-triphosphate (GTP) or guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S). In GTP-loaded cells, both acetylcholine (ACh) and adenosine (Ado) induced a specific K channel current through GTP-binding proteins by binding to the muscarinic and Ado receptors, respectively. Both cibenzoline and disopyramide suppressed the ACh-induced K current effectively in a concentration-dependent manner. The concentrations for half-maximal inhibition of the current (EC50) caused by cibenzoline and disopyramide were 8 and 3 microM, respectively. In GTP gamma S-loaded cells, the K current was irreversibly activated because GTP binding proteins were directly elicited by GTP gamma S. Cibenzoline effectively caused a decrease in the GTP gamma S-induced K current, whereas the extent of disopyramide action on the GTP gamma S-induced K current was much less. Cibenzoline also caused significant inhibition of Ado-induced K current in GTP-loaded cells. However, the action of disopyramide was less effective in inhibiting Ado-induced K current. These results indicate that cibenzoline has less potent anticholinergic effects than disopyramide in atrial myocytes. In addition, cibenzoline effectively inhibits the muscarinic K channel itself and/or GTP-binding proteins coupled to the channel, whereas the effect of disopyramide is attributed mainly to blockade of muscarinic receptors. These findings provide novel understanding of the molecular mechanism of anticholinergic action of cibenzoline.

Animals↗

PubMed1994

Prophylactic effect of mianserin on recurrent depression.

The prophylactic effect of mianserin on recurrent depression was studied in a double-blind comparison with an inactive placebo by analyzing the recurrence rate and the number of depressive episodes in 9 mianserin-treated (daily dose 20-60 mg) and 13 placebo-treated patients. The selected patients were those who had a higher incidence of recurrence (more than 2 depressive episodes during the 2 years preceding the study). During the 18-month study period, 4 of 9 mianserin-treated patients and all 13 placebo-treated patients had recurrences. The ratio between patients with recurrence and total patients (recurrence ratio) was lower in the mianserin-treated group throughout the study, and the intergroup difference from the 3rd to the 18th month was significant. In the mianserin-treated group, the frequency of episode recurrence during the study period was significantly lower and the total duration of episodes was significantly shorter than those in the placebo-treated group. The treatments did not differ significantly in safety. These results clearly indicate that mianserin is effective in the prophylaxis of recurrent depressive episodes.

Adult↗

PubMed1994

[Endocrinological examination and its clinical significance in manic-depressive illness].

Neuro-endocrine test is one of the useful strategies in examining the pathophysiology of manic-depressive illness (MDI). Unfortunately, however, the pathophysiology of MDI has not yet been clarified and the specific biological markers of MDI have still not been found. In the present paper, a brief general survey as to main clinical points of endocrinological examination and its results towards the hypothalamic-pituitary-adrenal axis, the hypothalamic-pituitary-thyroid axis, the hypothalamic-pituitary-gonadal axis, growth hormone, melatonin, etc. are given and some mentions of biological markers in MDI are made.

Adrenocorticotropic Hormone↗