Search PubMed⌕ Search

Biomedical subjects

A Takanaka

Publications and source records attributed to A Takanaka.

At least 37 records · Page 2Linked to original sources
PubMed1992

Indium inhibits gap junctional communication between rat hepatocytes in primary culture.

The effect of indium on gap junctional communication was investigated in primary cultured rat hepatocytes. Treatment of hepatocytes with indium chloride at concentrations of 100 microM to 1 mM for 2 h resulted in dose-dependent inhibition of gap junctional communication between hepatocytes. The effect of indium on hepatocytes was also evaluated using two indices for cell viability: lactate dehydrogenase (LDH) leakage and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction. Indium did not cause any increase in LDH leakage from hepatocytes at the above concentrations, but inhibition of MTT reduction was observed at concentrations above 500 microM. These results suggest that the gap junctions between hepatocytes may be vulnerable sites to indium toxicity.

Animals↗
PubMed1992

[Studies on the teratogenic potential of p-tert-butylphenolformaldehyde resin in rats].

p-tert-Butylphenolformaldehyde resin, an adhesive, was given orally to pregnant Wistar rats by stomach intubation at the dose levels of 250, 500 and 1000 mg/kg body weight during days 7 to 17 of gestation, and the effects of the compound on dams and fetal developments were examined. No changes in general conditions, maternal body weight, food consumption, numbers of corpora lutea and implantation ratio were observed. There was no evidence of an increase in fetal death or of malformation attributable to the treatment with p-tert-butylphenolformaldehyde resin in any of dose levels examined. It was concluded that p-tert-butylphenolformaldehyde resin has no teratogenic effect in rats.

Administration, Oral↗
PubMed1991

Inhibition of Ca-channels by diazepam compared with that by nicardipine in pheochromocytoma PC12 cells.

The effects of diazepam on voltage-gated Ca channels were studied in PC12 pheochromocytoma cells using whole-cell voltage-clamp techniques. An inward current activated by a depolarizing voltage step to +10 mV from a holding potential of -60 mV in 10.8 mM Ba was larger than that activated in 10.8 mM Ca. The Ba current was completely blocked by a low concentration of Cd (30 microM) and was also sensitive to nicardipine (100 nM to 10 microM). Diazepam (1-100 microM) inhibited the Ba current in a concentration-dependent manner. Neither diazepam nor nicardipine affected the current-voltage relationship or the dependence on holding potentials of the Ba current. Both slightly accelerated the inactivation time course of the Ba current. When diazepam was applied to the cells in combination with nicardipine, the observed inhibition agreed with a value predicted assuming independent blockade by diazepam and by nicardipine. These results suggest that diazepam inhibits Ca channels in a manner similar to nicardipine, but that the binding sites for diazepam are different from those for nicardipine.

Animals↗
PubMed1991

Effects of ATP antagonists on purinoceptor-operated inward currents in rat phaeochromocytoma cells.

The effects of suramin, reactive blue 2 (RB2) and d-tubocurarine (d-TC) were investigated electrophysiologically to elucidate the mechanisms underlying their antagonism of P2 purinoceptor-mediated responses. All three compounds inhibited an adenosine triphosphate (ATP)-activated inward current in rat phaeochromocytoma PC12 cells in a concentration-dependent manner. The order of potency was RB2 greater than suramin greater than d-TC. The inhibition induced by suramin or RB2 was reversible, whereas that induced by d-TC was not reversed after a 5-min rinse. The inactivation of the ATP-activated current was accelerated by d-TC but not by suramin or RB2. RB2 administered simultaneously with ATP exerted much weaker inhibition compared to that induced by prior administration, suggesting that RB2 is a slowly acting antagonist. This was not observed for suramin or d-TC. Suramin and RB2 caused a parallel shift in the concentration/response curve for the ATP-activated current. With d-TC the maximal response of ATP was decreased but the concentration producing half-maximal response was unchanged. The voltage dependency of the ATP-activated current showed less inward rectification in the presence of d-TC. Suramin or RB2 did not affect the voltage dependency. These results suggest that suramin and RB2 reversibly block binding of ATP to receptors, whereas d-TC blocks ion permeability through the ATP-activated channel.

Adenosine Triphosphate↗
PubMed1991

Selective and competitive antagonism by suramin of ATP-stimulated catecholamine-secretion from PC12 phaeochromocytoma cells.

1. Suramin, a putative P2-antagonist, (10 to 300 microM) inhibited the adenosine 5'-triphosphate (ATP)-stimulated secretion of [3H]-noradrenaline or endogenous dopamine from phaeochromocytoma PC12 cells in a concentration-dependent manner. Suramin (300 microM) did not affect the dopamine-secretion stimulated by high K+ or nicotine. 2. Suramin shifted the concentration-response curve for ATP to the right. The antagonism was competitive with a pA2 value of 4.52. 3. ATP also stimulated an increase in intracellular Ca2+ concentration as determined by fura-2 methods. Suramin antagonized this effect over the same concentration range that antagonized the ATP-stimulated catecholamine secretion. 4. These results suggest that suramin can be used as a selective and competitive antagonist of ATP in experiments concerning mechanisms of catecholamine-secretion.

Adenosine Triphosphate↗
PubMed1991

Antagonism by reactive blue 2 but not by brilliant blue G of extracellular ATP-evoked responses in PC12 phaeochromocytoma cells.

1. The effects of reactive blue 2 and brilliant blue G, which have been shown to block extracellular ATP-evoked responses, were investigated to discover whether these compounds act as P2-purinoceptor antagonists in PC12 phaeochromocytoma cells. 2. Reactive blue 2 (10 to 100 microM) suppressed the ATP-stimulated dopamine secretion from PC12 cells in a dose-dependent manner. The concentration-response curve for ATP was shifted to the right and the maximal response was decreased by reactive blue (30 and 100 microM). Brilliant blue G (up to 100 microM) did not significantly affect the secretion. 3. Reactive blue 2 (10 to 100 microM) suppressed the ATP-activated inward current recorded from the voltage-clamped cells in a concentration-dependent manner. Brilliant blue G (up to 100 microM) did not affect the current. 4. The results suggest that reactive blue 2 but not brilliant blue G is a P2-purinoceptor antagonist in PC12 cells. The purinoceptors in these cells may be the same type as those involved in ATP-evoked smooth muscle relaxation, judging from the antagonism by reactive blue 2.

Adenosine Triphosphate↗
PubMed1991

Comparison of adenosine triphosphate- and nicotine-activated inward currents in rat phaeochromocytoma cells.

1. The adenosine triphosphate (ATP)-activated inward current was compared to the nicotine-activated inward current in nerve growth factor (NGF)-treated rat phaeochromocytoma PC12 cells. 2. Both ATP and nicotine activated an inward current at negative holding potentials. The concentration of ATP necessary to activate the inward current was about 10-fold higher than that of nicotine; the EC50 was 20.5 microM for ATP and 2.4 microM for nicotine. The maximal responses induced by ATP and nicotine were almost identical in the same cells. The current-voltage relationship for the ATP-activated current was very similar to that for the nicotine-activated current, and both currents reversed around 0 mV in a physiological saline. 3. The ATP-activated current and the nicotine-activated current were not additive; the current activated by a combined administration of ATP (100 microM) and nicotine (10 microM) was only about 20% larger than the current activated by either ATP or nicotine alone. Nicotine (100 microM) did not increase the current activated by 1 microM-ATP. 4. ATP could activate an inward current in the cells even after desensitization to nicotine had developed. 5. Hexamethonium (100 microM) selectively blocked the nicotine-activated current whereas suramin (100 microM), a purinoceptor antagonist, selectively blocked the ATP-activated current. 6. Ionic selectivity was studied by changing compositions of extracellular solutions. When external Na+ was replaced with Cs+, both ATP and nicotine activated inward currents. However, with an extracellular solution containing Tris or glucosamine as a major cation, only ATP, not nicotine, activated an inward current. 7. ATP- and nicotine-activated currents were also recorded from cells bathed in a solution containing 1.8 mM-Ca2+ as the only external cation, suggesting that both pathways are Ca2+ permeable. 8. The results suggest that the ATP-sensitive ionic pathway is not independent of the nicotine-sensitive pathway in these cells. Our working hypothesis is that ATP and nicotine activate the same channels but the binding sites and the open-states of the channels are different between these two agonists.

Adenosine Triphosphate↗
PubMed1991

Inhibition of ion channels by hirsutine in rat pheochromocytoma cells.

Effects of hirsutine, an alkaloid that produces a potent ganglion blocking effect, were investigated using rat pheochromocytoma PC12 cells. Hirsutine (1 to 10 microM) suppressed dopamine-release evoked by 100 microM nicotine. In voltage-clamped cells, hirsutine (1 to 10 microM) inhibited the inward current activated by 100 microM nicotine. Hirsutine was equipotent to hexamethonium in blocking the nicotine-activated current. The voltage-dependency of the nicotine activated current was not modified by hirsutine. Effects of hirustine on other ion channels were tested to determine its selectivity. Inward currents mediated through ATP-activated channels were scarcely affected by hirsutine (up to 100 microM). However, hirustine (10 microM) inhibited Ba currents passing through Ca channels and K currents activated by depolarizing voltage steps. The results suggest that hirsutine potently blocks nicotinic receptor-channels, but hirsutine also inhibits voltage-gated Ca and K channels. Roles of the inhibition of these channels in the pharmacological effects of hirsutine were discussed.

Adrenal Gland Neoplasms↗
PubMed1991

[Studies on the uptake of 8-anilino-1-naphthalene sulfonate by rat freshly isolated renal cells].

The addition of 8-anilino-1-naphthalene sulfonate (ANS) into rat renal cell suspension caused a rapid increase in fluorescence (Ex. 400 nm, Em. 470 nm). The increase in fluorescence seemed to be composed of two phases. When the cells were disrupted by ultrasonic wave, the fast phase (0-ca 20 sec) increased and the slow phase (after ca 40 sec) disappeared. The rate of increase in the slow phase was dependent on the concentration of ANS and on the ambient temperature. A double reciprocal plot of the rate and the concentration exhibited straight line. It was decreased by bromophenol blue and rose bengal but not by other organic anions like p-aminohippuric acid and several metabolic inhibitors. It seemed that the uptake of ANS into the renal cell is mediated by a carrier which is different from that for p-aminohippuric acid.

Anilino Naphthalenesulfonates↗
PubMed1991

[Studies on the teratogenic potential of 2,2'-isobutylidene-bis (4,6-dimethylphenol) in rats].

2,2'-Isobutylidene-bis(4,6-dimethylphenol), an antioxidant, was given orally to pregnant Wistar rats by stomach intubation at the dose levels of 5, 15 or 45 mg/kg body weight during days 7 to 17 of gestation, and the effects of the compound on dams and fetal developments were examined. In the dams at the two higher dose levels of 15 and 45 mg/kg, toxic signs (tremor, startle reflex, salivation, involuntary urination, wheezing and nostril discharge) were observed. Moreover, at the highest dose level, additional toxic signs (lacrimation and vaginal bleeding), suppression in maternal body weight gain and food consumption were observed. However, there was no evidence of an increase in malformations attributable to the treatment with 2,2'-isobutylidene-bis(4,6-dimethyl-phenol) in any of the treated groups. It was concluded that 2,2'-isobutylidene-bis(4,6-dimethylphenol) has no teratogenic effect in rats, though toxic signs were observed in treated dams of the 15 and 45 mg/kg groups.

Administration, Oral↗
PubMed1991

Inhibitory action of peripheral-type benzodiazepines on dopamine release from PC12 pheochromocytoma cells.

Characteristics of the benzodiazepine inhibition of dopamine (DA) release in PC12 cells were investigated. Diazepam inhibited DA release evoked by high concentrations of extracellular K+ in a dose-dependent manner (IC50, 10 microM). Ro 5-4864 [7-chloro-1,3-dihydro-1-methyl-5-(p-chlorophenyl)-2H-1,4-benzodiazepine- 2-one], a peripheral-type benzodiazepine, also inhibited DA release effectively. PK 11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methyl-propyl)-3-isoquinoline carboxamide], a benzodiazepine generally considered a peripheral-type benzodiazepine receptor antagonist, did not antagonize the inhibition induced by diazepam, but rather inhibited DA release itself. On the other hand, the central-type benzodiazepines, clonazepam and Ro 15-1788 (ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5a] [1,4]benzodiazepine-3-carboxylate) did not affect the DA release. Diazepam, Ro 5-4864 and PK 11195 also inhibited a Ba(++)-current carried by voltage-gated Ca++ channels, and diazepam suppressed an increase in intracellular Ca++ evoked by 80 mM extracellular K+ as measured by the fura-2 method. These results suggest that the inhibitory action of diazepam and other benzodiazepines on DA release from PC12 cells may be mediated through one type of peripheral-type benzodiazepine receptors which are coupled to voltage-gated Ca++ channels and that these receptors may not necessarily be the same as those in other tissues.

Animals↗
PubMed1990

ATP-activated single-channel currents recorded from cell-free patches of pheochromocytoma PC12 cells.

Single-channel recordings were made using cell-free membrane patches (outside-out configuration) isolated from pheochromocytoma PC12 cells. ATP (50 microM) activated single channel currents in the isolated patches and the currents inactivated with a half-decay time of about 5s. The single channel conductance was about 13 pS in external solution with 140 mM Na. The amplitudes of the single-channel currents were decreased when external Ca was increased from 1.8 to 16.2 mM, suggesting that Ca blocks ion permeation through the channel. These properties of single-channel currents may underlie those of the macroscopic current.

Adenosine Triphosphate↗
PubMed1990

Neurokinin A suppresses a voltage-gated K+ current in smooth muscle cells from rat vas deferens.

The effects of neurokinin A (NKA) on freshly isolated smooth muscle cells from the rat vas deferens were investigated electrophysiologically. NKA (10(-7) M) prolonged the duration of action potentials without affecting resting potentials. Under voltage-clamp conditions, NKA (10(-7) M) suppressed an outward K+ current activated by depolarizing voltage steps. Substance P (SP, 10(-7) M) did not affect the K+ current, suggesting that NKA is more potent in suppressing the K+ current than SP is, as is also true for the contractions of smooth muscles of the rat vas deferens. The suppression of the K+ conductance now reported may contribute to NKA-induced smooth muscle contraction.

Action Potentials↗
PubMed1990

Difference between substance P- and acetylcholine-induced currents in mammalian smooth muscle cells.

The effects of substance P (SP) and acetylcholine (ACh) on membrane currents were compared using freshly isolated smooth muscle cells from guinea-pig ileum. Both SP (100 nM) and ACh (10 microM) induced inward currents at negative holding potentials. The ACh-induced current, but not the SP-induced current, showed relaxation upon voltage-stepping. The SP-induced current was increased by hyperpolarization more negative than -50 mV whereas the ACh-induced current was decreased by hyperpolarization. The results suggest that the SP-induced inward current is elicited via an ionic pathway different from that involved with ACh-activated channels.

Acetylcholine↗
PubMed1990

Aflatoxin B1-specific cytochrome P-450 isozyme (P-450-AFB) inducible by 3-methylcholanthrene in golden hamsters.

Hepatic microsomes of polychlorinated biphenyl (PCB)-treated Syrian Golden hamsters possessed a higher potency toward aflatoxin B1 activation, based on the Ames test, than other animal species. This activity was induced in hamsters preferentially by treatment with 3-methylcholanthrene rather than phenobarbital. The contribution of an isozyme of cytochrome P-450 (P-450-AFB) to the activity of hamster livers for aflatoxin B1 was studied. P-450-AFB, purified from 3-methylcholanthrene-treated hamster livers, was shown to possess the highest activation of aflatoxin B1 in the Ames test. The quantification of this isozyme by a fluorometric sandwich enzyme-linked immunosorbent assay (ELISA) demonstrated that P-450-AFB was induced mainly in Syrian Golden hamsters but not in Chinese hamsters, or in other species. This isozyme constitutes approximately 40% of the total cytochrome P-450 of the hepatic microsomes from 3-methylcholanthrene-treated Golden hamsters but only 1% in the microsomes of phenobarbital-treated hamsters. Thus, we conclude that the high activity of Golden hamster livers towards aflatoxin B1 activation was due presumably to this distinct and unique cytochrome P-450 isozyme which was induced mainly by 3-methylcholanthrene in Golden hamsters.

Aflatoxin B1↗
PubMed1990

Reversible and selective antagonism by suramin of ATP-activated inward current in PC12 phaeochromocytoma cells.

1. The effects of suramin on an adenosine 5'-triphosphate (ATP)-activated inward current were investigated in PC12 phaeochromocytoma cells with whole-cell voltage-clamp techniques. 2. Suramin (30 to 300 microM) inhibited the ATP-activated current in a dose-dependent manner. The inhibitory effects were reversible and competitive. 3. Suramin also suppressed the current activated by adenosine 5'-O-(3-thiotriphosphate) but did not affect the current activated by nicotine. Suramin did not affect the suppression of a K current induced by methacholine. 4. The results suggest that suramin antagonizes the ATP-receptor-operated membrane current reversibly and selectively.

Adenosine Triphosphate↗
PubMed1990

An ATP-activated conductance in pheochromocytoma cells and its suppression by extracellular calcium.

1. ATP-activated inward current in PC12 pheochromocytoma cells was characterized using the whole-cell voltage-clamp technique. 2. ATP (100 microM) applied extracellular elicited an inward rectifying current with a reversal potential of about +7 mV. The current was desensitized in seconds in spite of continued presence of ATP. 3. A comparison was made of the ability of ATP and its analogues. The order of potency in activating the inward current was ATP greater than ATP gamma S greater than ADP; AMP, adenosine and alpha, beta-methylene ATP were inactive at concentrations up to mM. 4. The ATP-activated current was also observed when external Na+ and Ca2+ were replaced with K+, TEA, Tris or glucosamine. The order of ion selectivity was Na+ greater than K+ greater than TEA not equal to Tris greater than glucosamine. 5. The ATP-activated current was also recorded in extracellular solutions containing Ca2+ as the only external cation. The amplitude increased as the concentration of Ca2+ was increased in the range between 1.8 and 16.2 mM. However, the current amplitude decreased at higher Ca2+ concentrations and the current was not recorded in 110 mM-Ca2+ solution. 6. In the presence of 140 mM-Na+ in the external solution, the current amplitude also decreased as the external Ca2+ concentration was increased (from 1.8 to 16.2 mM). 7. The results indicate that Ca2+ as well as monovalent cations permeate through the ATP-sensitive pathway and that Ca2+ blocks ion permeation, including its own permeation through the pathway. This regulation by extracellular Ca2+ is different to the ATP-activated current in smooth muscle cells.

Adenosine Triphosphate↗