Biomedical subjects

N Taira

Publications and source records attributed to N Taira.

At least 37 records · Page 2Linked to original sources

PubMed1996

A consideration on the relationship between worm age and mortality of Setaria marshalli recovered from the peritoneal cavity of calves born in Tottori prefecture, Japan.

Eight calves born in November-December of 1992 were necropsied at the age of 29-230 days in an attempt to estimate the life span of Setaria marshalli in Japan. Worm ages were estimated on the base of active season for mosquitoes. Thirty worms estimated 4-9 months old recovered from 4 calves were all alive in the peritoneal cavity. Thirty-five out of 50 worms estimated 7-13 months old were dead with being entrapped by fibrin on the peritoneum. It is speculated that this is a normal fate of this parasite at the end of its life, and therefore, the life span of S. marshalli would be approximately one year after prenatal infection.

Aging↗

PubMed1995

The voltage-dependent K+ channel (Kv1.5) cloned from rabbit heart and facilitation of inactivation of the delayed rectifier current by the rat beta subunit.

We have isolated a cDNA coding for a delayed rectifier K+ channel (RBKV1.5) from rabbit heart. The amino acid sequence of RBKV1.5 displays a homology to that of other K+ channels of Kv1.5 class. Overall amino acid identity between RBKV1.5 channel and Kv1.5 channel of other species is about 85%. RNA blot analysis revealed the expression of the primary transcript in various rabbit tissues, at the highest level in both the atrium and ventricle. When expressed in Xenopus oocytes, RBKV1.5 current showed a delayed rectifier type characteristics, which was converted to rapidly inactivating currents upon coexpression with a beta subunit.

Amino Acid Sequence↗

PubMed1995

Antiarrhythmic and bradycardic drugs inhibit currents of cloned K+ channels, KV1.2 and KV1.4.

We investigated the effects of the antiarrhythmic drugs, quinidine, disopyramide, flecainide, clofilium, verapamil, and the bradycardic drug, bertosamil, on the currents of the cloned K+ channels, KV1.2 (IK(V1.2)) and KV1.4 (IK(V1.4)), using the Xenopus oocyte expression system. Both IK(V1.2) and IK(V1.4) were inhibited in a concentration-dependent manner by quinidine (10 microM to 1 mM), flecainide (10 microM to 1 mM), clofilium (10-300 microM), verapamil (10 microM to 1 mM) and bertosamil (10 microM to 1 mM) but not by disopyramide (10 microM to 1 mM). The inhibitory effects of clofilium, verapamil and bertosamil on IK(V1.2) were time-dependent. The decay time course of IK(V1.4) was accelerated by clofilium, verapamil and bertosamil, but decelerated by quinidine and flecainide. These results indicate that IK(V1.2) and IK(V1.4) are targets for the four antiarrhythmic drugs and the bradycardic drug.

Animals↗

PubMed1995

Cloning of a swelling-induced chloride current related protein from rabbit heart.

Recently, pIcln has been reported to be a regulator of a swelling-induced chloride conductance. We have cloned a cDNA RCL-H1 from rabbit heart, of which primary structure is highly homologous to that of pIcln. Outwardly rectifying currents were recorded in oocytes expressing RCL-H1, which is consistent with the result of pIcln. RNA blot analysis revealed the widespread expression of RCL-H1 mRNA in rabbit tissues. RCL-H1 may play an important role in regulating cell volume and give a clue to revealing molecular structure of swelling-induced chloride channel(s).

Amino Acid Sequence↗

PubMed1995

Effects of semotiadil fumarate, a novel Ca2+ antagonist, on cytosolic Ca2+ level and force of contraction in porcine coronary arteries.

1. The mechanisms of action of semotiadil fumarate, a novel Ca2+ antagonist, were examined by measuring the cytosolic Ca2+ level ([Ca2+]i) and force of contraction in porcine coronary arteries, and by determining [3H]-pyrilamine binding to bovine cerebellar membranes. 2. Semotiadil or verapamil (0.1 and 1 microM) inhibited both the high KCl-induced increases in [Ca2+]i and force in a concentration-dependent manner. 3. Histamine (30 microM) produced transient increases followed by sustained increases in [Ca2+]i and force, which were inhibited by semotiadil and verapamil (1 and 10 microM). The agents were different in that semotiadil reduced the maximum [Ca2+]i and force responses to histamine, but not pD2 values, whereas verapamil did reduce the pD2 values for histamine, but not the maximum responses. 4. Verapamil (10 microM), but not semotiadil, inhibited histamine-induced increases in [Ca2+]i and force in Ca(2+)-free solution. Neither semotiadil nor verapamil affected the increases in [Ca2+]i and force induced by caffeine. Semotiadil even at the higher concentration (10 microM) did not displace specific binding of [3H]-pyrilamine to bovine cerebellar membranes. 5. These results suggest that semotiadil inhibits both KCl- and histamine-induced contractions mainly by blocking voltage-dependent L-type Ca2+ channels.

Animals↗

PubMed1995

Determination of KA values by controlled receptor expression in Xenopus oocytes.

1. In the present study we estimated the KA value of endothelin-1 (ET-1) for ETA-receptors by a new method in which the level of expression of ETA-receptors in Xenopus oocytes was altered in a controlled way. 2. Kvl.2 (a delayed rectifier type K channel) c RNA at the fixed concentration of 0.2 micro g micro l(-1) was mixed with ETA-receptor cRNA at various concentration ratios (10(-3)-3). Oocytes were examined 2-4 days after the injection of the cRNA mixtures. 3. In these oocytes, ET-1 suppressed the amplitude of Kvl.2 current in a dose-dependent manner in the range of 0.1-100 nM; the maximum inhibition produced by ET-1 was larger and the EC50 value for the inhibition by ET-1 was smaller as the mixture ratio was increased. Double-reciprocal plots of equiactive concentrations of ET-1 in 1/1- and 1/30-injected oocytes yielded a KA for ET-1 of 7.4 nM. The number of ETA-receptors in 1/30-injected oocytes was 13% of that in 1/1-injected oocytes, whereas the inhibition of the current in 1/30-injected oocytes was about 60% of that in 1/1-injected oocytes. This suggests the presence of spare receptors of ETA in the latter. 4. A saturation binding experiment estimated a KD value of 0.1 nM for ET-1 at ETA-receptors and the number of ETA-receptors in 1/30-injected oocytes was 23% of that in 1/1-injected ones. This value was not significantly different from that estimated by the above new method. However, there was a discrepancy between KA and KD, which could be due to factors unique to the expression system employed in the present study.

Analysis of Variance↗

PubMed1995

Massive experimental infection with Strongyloides venezuelensis in rats and absence of sudden death.

Ten rats were divided into five groups, A - E, to determine the larval dose-effect of infection with Strongyloides venezuelensis (SVZ). The rat groups were exposed to SVZ infective larvae as follow: (A) 100, (B) 1,000, (C) 10,000, (D) 100,000 and (E) 1,000,000. The eight rats in Groups A - D survived the infection. Rats exposed to the higher doses of larvae had the higher egg per gram counts (EPG), but more rapid reduction in EPG counts. The four rats in Groups C and D had EPG counts greater than 10,000 EPG during days 7 - 21 after infection. Maximum EPG values in Group C were 85,400 and 106,600; those in Group D were 134,000 and 346,000. The two rats in Group E showed severe itching and bleeding on their digital pads at the time of infection. They became listless thereafter and died with hemorrhagic pneumonia at 4 days after infection. The sudden death that has been demonstrated in calves infected with massive doses of S. papillosus was not observed in SVZ-infected rats.

Animals↗

PubMed1994

Hybrid potassium channels by tandem linkage of inactivating and non-inactivating subunits.

We constructed tandem cDNA by linking the 5' end of a delayed rectifier-type (Kv1.2) clone to the 3' end of a transient-type (Kv1.4) K+ channel clone. Fusion genes were also constructed, consisting of Kv1.4 and mutants of Kv1.2, which have a single amino acid substitution in the S4-S5 loop. From electrophysiological characterization, it is likely that two pairs of tandem heterodimer constructs can form hybrid channels. In addition, it has been revealed that the wild-type hybrid channel shows a time constant of inactivation very similar to that observed in the homotetrameric Kv1.4 channel. Difference of inactivation kinetics between wild-type and mutant hybrid K+ channels suggests that not only the S4-S5 loop of Kv1.4 but also that of Kv1.2 can serve as the acceptor sites for the inactivation gates, and that all of four sets of loops should be functional for rapid inactivation. From these results, in the hybrid channels the structure and composition of the acceptor sites could be important factors for determining the rate of inactivation.

Amino Acid Sequence↗

PubMed1994

Receptor-mediated modulation of rat KV1.2 in Xenopus oocytes.

To investigate mechanisms for the receptor-mediated inhibition of a rat cardiac K+ channel clone (KV1.2), we coexpressed KV1.2 with a subtype of endothelin receptors (ETA) in Xenopus oocytes. Effects of endothelin ETA receptor stimulation were mimicked by application of PMA (4-beta-phorbol 12-myristate 13-acetate; 0.1 microM) or intracellular injection of CaCl2 (estimated concentration of 1 microM). These effects diminished in the presence of staurosporine (1 microM) or EGTA (estimated concentration of 5 mM). These results suggest that both activation of protein kinase C and an increase in intracellular Ca2+ contribute to the suppression.

Alkaloids↗

PubMed1994

Cloning and functional expression of a cardiac inward rectifier K+ channel.

We have isolated a cDNA coding for an inward rectifier K+ channel (RBHIK1) from rabbit heart. The cloned cDNA encodes a protein of 427 amino acids with two putative transmembrane segments. The primary structure of RBHIK1 is highly homologous to that of IRK1 which is an inward rectifier K+ channel recently cloned from mouse macrophage by expression cloning. When expressed in Xenopus oocytes, RBHIK1 current showed strong inward rectification and was inhibited by extracellular Ba2+ and Cs+. RNA blot analysis revealed the expression of RBHIK1 mRNA in various rabbit tissues, especially high level in the ventricular muscle.

Amino Acid Sequence↗

PubMed1994

Relaxant mechanisms of cyclic AMP-increasing agents in porcine coronary artery.

We investigated the relaxant mechanisms of the cyclic AMP (cAMP)-increasing agents, isoproterenol, T-0509, forskolin and 3-isobutyl-1-methylxanthine (IBMX), on porcine coronary arteries contracted with U46619 (300 nM), a thromboxane A2 analogue, or 30 mM KCl, by measuring force simultaneously with intracellular Ca2+ concentration ([Ca2+]i) or cAMP and cyclic GMP (cGMP) levels. In U46619-contracted arteries, these agents decreased [Ca2+]i and force of contraction to almost the same extent in a concentration-dependent manner, whereas in KCl-contracted arteries these agents, except IBMX at higher concentrations, produced a relaxation with little change in [Ca2+]i. These agents all elevated tissue cAMP levels, and in addition, IBMX at higher concentrations increased cGMP levels. In Ca(2+)-free medium, these agents produced a concentration-dependent inhibition of Ca2+ release from intracellular Ca2+ stores induced by U46619 but not by 25 mM caffeine. Isoproterenol at a high concentration (3 microM) transiently decreased [Ca2+]i but steadily relaxed KCl-contracted arteries. This decrease in [Ca2+]i, but not the relaxation was inhibited by ryanodine and caffeine treatments. These results suggest that the relaxant mechanism of these agents on KCl-contracted arteries is mainly due to phosphorylation of myosin light chain kinase via cAMP-dependent protein kinase, resulting in a reduction of the Ca2+ sensitivity of contractile elements. Their relaxant mechanism in U46619-contracted arteries seems due to the inhibition of signal transduction of the agonist, resulting in a decrease in [Ca2+]i and inhibition of the Ca2+ sensitization.

1-Methyl-3-isobutylxanthine↗

PubMed1994

A further study of the vasodilator and negative inotropic mechanisms of action of nicorandil and its congeners in the canine heart.

The vasodilator and negative inotropic mechanisms of action of nicorandil and its congeners (SG-209, SG-103, and SG-86) were investigated in isolated canine papillary muscle preparations cross-circulated through the anterior septal artery with support dogs. SG-209, SG-103, and SG-86 were obtained by replacement of the nitroxyl group of nicorandil by acetoxyl, nicotinoyloxyl, and hydroxyl groups, respectively. Nicorandil (0.03-10 mumol), SG-209 (0.1-10 mumol), SG-103 (1-30 mumol), and SG-86 (3-100 mumol) all produced an increase in coronary blood flow through the anterior septal artery. Both nicorandil and SG-209 produced a near-maximal increase in coronary blood flow, the latter being about 5.5 times less potent than the former. SG-103 and SG-86 were far less potent than SG-209 in that order. The vasodilator actions of nicorandil and SG-209 were antagonized by glibenclamide given IV to support dogs, but those of SG-103 and SG-86 were not. The pKB values of glibenclamide were 6.34 toward nicorandil and 6.49 toward SG-209. Developed tension of the papillary muscle was reduced by nicorandil, SG-209, and SG-103, but not by SG-86. In this respect SG-209 was about 4.7 times less potent than nicorandil, and SG-103 was much less potent than SG-209. The negative inotropic effects of nicorandil and SG-209 were antagonized by glibenclamide, but that of SG-103 was not.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

A possibility that the ATP-sensitive potassium channel in coronary artery has a high-affinity internal binding site for tetraalkylammonium.

The functionally responsible sites for the blocking action of tetraalkylammonium ions (TAAs) in ATP-sensitive K+ (KATP) channels opened by levcromakalim were estimated in canine coronary artery. Tetraethylammonium (TEA) and tetrabutylammonium (TBA) inhibited the levcromakalim-induced relaxation in a noncompetitive manner. Analyses of the noncompetitive antagonism revealed that the binding constant of TBA was about 900 times lower than that of TEA, although the reported affinity of TBA for the internal binding site in various K+ channels was only 10 times higher than that of TEA. TBA is much more lipid-soluble and permeable through membranes than TEA. Thus, TBA blocks KATP channels by binding to a possible high-affinity internal site for TAAs, whereas TEA seems to bind to the external site.

Adenosine Triphosphate↗

PubMed1994

Wasting condition under normal cardiac rhythms in rabbits following Strongyloides papillosus infection.

Pathogenicity of Strongyloides papillosus to rabbits was investigated by monitoring of food intake, body weight and electrocardiogram. No abnormalities were observed in rabbits infected with 10(4) infective larvae (L3)/kg. Rabbits given 10(5) L3/kg exhibited anorexia after the establishment of patent infections. Four of them died on Days 19-33 having lost 32-44% of initial body weight. The other one animal regained appetite and body weight as fecal egg output decreased. Cardiac rhythms remained normal even in the emaciation state. In lethal cases, cardiac activities finally disappeared through escape beats preceded by sinus arrhythmia as in a fasted control. These results suggest that heavy S. papillosus infection produces a wasting condition in rabbits resulting from anorexia under normal cardiac functions.

Animals↗

PubMed1994

Efficacy of ivermectin against Setaria microfilariae in calves and cerebrospinal setariosis in sheep and goats.

Ten calves harboring microfilariae (Mf) were injected with ivermectin at a single dose of 200 micrograms/kg body weight. Thereafter, the number of calves harboring Mf was gradually reduced to 7, 2 and 0 by 1, 4 and 12 weeks, respectively and remained negative for microfilariae by 16 weeks after injection. Furthermore, none of 221 goats and sheep injected twice with ivermectin at a dose of 200 micrograms/kg body weight developed setariosis while 17 out of 303 non-injected animals suffered from that disease. Therefore, ivermectin was much effective for the eradication of Mf in calves and the prevention of setariosis in sheep and goats.

Animals↗

PubMed1994

Two cases of parafilariasis in dairy cattle and treatment of hemorrhage with levamisole topical application.

On June and August in 1989, cutaneous hemorrhagic parafilariasis was found in two cattle among 30 pregnant dairy cattle transported from Hokkaido to Chiba Prefecture. One adult female worm each was recovered from the blood spot in both cattle. Ivermectin oral administration, dosage rate of 200 micrograms/kg body weight, had no effect on the occurrence of the blood spots. Topical application of levamisole on a blood spot at a 2.5% concentration showed to stop the bleeding within a few minutes after treatment. This method was very easy to use at the farm situation where cutaneous hemorrhagic parafilariasis sporadically occurred. The disease has not been found in Chiba Prefecture on a whole since those cases in 1989.

Administration, Topical↗

PubMed1994

Isolation of Strongyloides venezuelensis from Rattus norvegicus in Kagoshima Prefecture.

On 30 August 1984, Strongyloides sp. specimens were isolated from a rat (Rattus norvegicus) trapped at a pig farm in Kiire-cho, Ibusuki-gun, Kagoshima Prefecture. Both anterior and posterior ovaries of parasitic female were spirally coiled. The means of body length and width, esophagus length, and the distances from mouth to vulva and from anus to tail end were 2,493, 34.5, 719.8, 1,682.8 and 54.4 microns respectively. Filariform larvae measured 544.2, 15.6 and 238.5 microns in the means of body length and width, and esophagus length respectively. These measurements of the present Strongyloides species agreed with those described for S. venezuelensis. Infection rate by oral administration of larvae was low, while subcutaneous inoculation and percutaneous exposure to larvae produced high infection rate to rats which discharged many egg in the feces. The present parasite has been passaged through rats (SD strain) in these 8 years. This isolate is designated as the Kagoshima strain of S. venezuelensis.

Animals↗

PubMed1994

Parasitic females of Strongyloides papillosus as a pathogenetic stage for sudden cardiac death in infected lambs.

The present study was aimed at elucidating the responsibility of parasitic females for sudden cardiac death following Strongyloides papillosus infection in calves. A preliminary experiment demonstrated a percutaneous infection with S. papillosus infective larvae to cause sudden cardiac death in lambs as in calves, indicating lambs could serve as a model to study fatal stronglyloidiasis in calves. Parasitic females of S. papillosus were inoculated into the duodenum of lambs. Lambs given live worms developed continuous sinus tachycardia immediately after inoculation, and died of sudden cardiac arrest by ventricular fibrillation through a phase of the disease identical to the case of percutaneous larval infection. The lambs had high fecal egg counts at the time of death. Inoculation of homogenized worms did not produce fatal arrhythmias. These results demonstrate that live parasitic females of S. papillosus in the small intestine are responsible for cardiac dysfunction regardless of the presence or absence of migratory larvae.

Animals↗