Biomedical subjects

S Mihara

Publications and source records attributed to S Mihara.

At least 73 records · Page 4Linked to original sources

PubMed1992

Possible implication of peptidase activity in different potency of angiotensins II and III for displacing [125I]angiotensin II binding in pig aorta.

A single class of [125I]angiotensin II ([125I]AII) binding sites was found in porcine aortic smooth muscle membranes. Des-Asp1-AII (AIII) and des-Asp1-[Ile8]AII were 20 times less potent than AII or [Sar1,Ile8]AII to displace [125I]AII binding. In contrast, AII and AIII equipotently induced an increase in cytosolic free Ca2+ concentration in cultured porcine aortic smooth muscle cells. Des-Asp1-[Ile8]AII and [Sar1,Ile8]AII equipotently inhibited the increase induced by either AII or AIII. In order to explain this discrepancy, we studied [125I]AIII binding. In the presence of amastatin or a potent inhibitor of aminopeptidase M, [125I]AII binding remained stable for 90 min, but [125I]AIII binding decreased gradually after the peak at 30 min. The decrease was completely blocked by the presence of amastatin and phenylmethylsulfonylfluoride. Consequently, AIII was as potent as AII to displace [125I]AII binding in the presence of these two protease inhibitors. These results suggest that the lower potency of AIII to displace [125I]AII binding is related primarily to AIII-specific degradation by proteases.

Aminopeptidases↗

PubMed1992

Non-isopeptide-selective endothelin receptors in human Girardi heart cells.

We characterized the endothelin (ET) receptor in Girardi heart (GH) cells derived from human atrium. The ET isopeptides ET-1, ET-2 and ET-3 induced the monotonous and long-lasting rise in cytosolic free Ca2+ concentration [( Ca2+]i) with almost the same potency in GH cells. Scatchard analysis of [125I]ET-1 and [125I]ET-3 binding revealed that GH cells have almost the same number of binding sites for either labeled ligand. All ET isopeptides displaced either [125I]ET-1 or [125I]ET-3 binding in GH cells almost equipotently. These results reveal that the functional ET receptors in GH cells are of the ETB-type. GH cells are the first cell line to be found to express the functional ETB-receptor.

Autoradiography↗

PubMed1992

Studies of temperature rise in bladder cancer and surrounding tissues during radiofrequency hyperthermia.

Temperatures in the tumor on the bladder wall, tumor margin, intravesical urine, rectal cavity and pubic subcutaneous fat tissue (SCFT) were measured in a total of 48 bladder tumor patients during radiofrequency (RF)-capacitive heating of the tumors. There were close correlations (p less than 0.01) between the temperature of the tumor margin and intratumor temperature, between the intravesical temperature and the temperature of the tumor margin, between the RF power applied and the intravesical temperature and also between the thickness and the temperature of SCFT. As long as the thickness of SCFT was 20 mm or less, it was possible to raise the temperature of bladder cancer to 42.5 degrees C or above. The intravesical temperature could be regarded as an indicator for hyperthermia treatment since the intravesical urine temperature of over 42 degrees C implied a therapeutic temperature of 42.5 degrees C or more in the margin of the tumor. Since the intravesical temperature was closely related to the output power, the therapeutic magnitude of the output power could be defined at least as 400 W, by which intravesical urine temperature could exceed 42 degrees C.

Adipose Tissue↗

PubMed1991

Two states of the L-type Ca2+ channel in PC12 cells: different sensitivity to 1,4-dihydropyridines.

A omega-conotoxin-resistant component of high K(+)-induced [Ca2+]i increase in PC12 cells was further divided into two components by the difference in sensitivity to 1,4-dihydropyridines. The initial phase (up to 30s) was several times less sensitive to 1,4-dihydropyridines than the following plateau phase (several minutes). On the other hand, diltiazem blocked both phases with the same potency. Verapamil also was only a little more sensitive to the initial phase. All four 1,4-dihydropyridines tested showed 5-10 times more potent inhibition of (+)-[3H]PN200-110 binding in PC12 cells under the depolarizing (70 mM K+) condition than under the non-depolarizing (5 mM K+) condition. The biphasic blockade of the high K(+)-induced [Ca2+]i rise by 1,4-dihydropyridines appears to reflect their different affinities under depolarizing and non-depolarizing conditions.

Calcium Channel Blockers↗

PubMed1991

Neuropeptide Y receptor in vascular smooth muscle.

125I-Bolton-Hunter (125I-BH) neuropeptide Y (NPY) was used to identify specific high-affinity NPY binding sites in porcine aortic smooth muscle membrane fractions and to characterize the binding sites in comparison with those in porcine hippocampal membrane fractions. Ca2+, but not Mg2+ or Mn2+, enhanced specific 125I-BH-NPY binding in aortic smooth muscle, while all of the cations did in hippocampus. The fast, saturable, and selective binding was to a single population of sites, with a KD of 0.99 +/- 0.11 nM and a Bmax of 0.35 +/- 0.06 fmol/mg protein. GTP and its non-hydrolyzable analogues reduced 125I-BH-NPY binding dose dependently. Neither calcium channel blockers nor noradrenaline had any effect on the binding. Among structurally related peptides, peptide YY displaced 125I-BH-NPY binding as potently as NPY, while human, avian, and rat pancreatic polypeptides displaced 125I-BH-NPY binding 100 times less potently than NPY. The C-terminal fragment NPY(13-36) for inhibiting 125I-BH-NPY binding in aortic smooth muscle was approximately 40 times less potent than in the hippocampus. When we examined the effect of these peptides on cytosolic free Ca2+ ([Ca2+]i) in cultured porcine aortic smooth muscle cells, only the peptides showing high affinity for 125I-BH-NPY binding sites increased [Ca2+]i. These results indicate that the NPY binding sites labeled by 125I-BH-NPY in aortic smooth muscle are functional receptors and have different properties from those in the hippocampus with respect to dependency on divalent cations, sensitivity to GTP analogues, and affinity for NPY(13-36) and pancreatic polypeptides.

Animals↗

PubMed1991

Mechanisms underlying intracellular signal transduction of the slow IPSP in submucous neurones of the guinea-pig caecum.

1. Intracellular recordings were obtained from submucous plexus neurones of the guinea-pig caecum. 2. The resting membrane conductance displayed two types of inward rectification: one which developed at potentials more negative than -70 mV, and another that occurred at potentials more negative than the potassium equilibrium potential. The former inward rectification was blocked by extracellular caesium (Cs+; 1-2 mM) and the latter was blocked by Cs+ (1-2 mM) or barium (Ba2+; 30-100 microM). 3. The noradrenaline-induced current measured by subtraction of the current-voltage (I-V) relation before and after adding the agonist also showed an inward rectification around the resting potential. Ba2+ (30-100 microM) blocked both the outward and inward current induced by noradrenaline. The noradrenaline current was not affected by Cs+ (1-2 mM). Both the slow IPSP and the slow IPSC (inhibitory postsynaptic current) were reduced by Ba2+, but not by Cs+. 4. During the intracellular injection of guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S), multiple repetitive stimulation or repeated applications of noradrenaline produced irreversible membrane hyperpolarizations with a decreased membrane input resistance, until the membrane had approached the potassium equilibrium potential. 5. Pertussis toxin (1-40 micrograms/ml) abolished both the slow IPSP and the noradrenaline hyperpolarization without affecting the nicotinic fast EPSP or the slow EPSP. 6. Superfusion with a Ca(2+)-free, high-Mg2+ (12 mM) solution caused a membrane depolarization associated with an increased input resistance. It eliminated the Ca2+ spikes, the slow after-hyperpolarizations following the spikes, and the synaptic potentials within 3 min. Prolonged exposure (longer than 20 min) to this solution resulted in a progressive decline of the noradrenaline hyperpolarization. 7. Intracellular injection of ethylene glycol-bis(beta-aminoethylether)N,N,N',N'-tetraacetic acid (EGTA) reduced the slow IPSP and the noradrenaline hyperpolarization. Superfusion with a membrane-permeable Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetraacetoxymethyl ester (BAPTA/AM; 10-200 microM) reduced the noradrenaline hyperpolarization. 8. Procaine reversibly reduced the slow IPSP and noradrenaline hyperpolarization without affecting the fast EPSP or slow EPSP at concentrations up to 300 microM.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Effect of S-312, a new calcium channel blocker, on the 1,4-dihydropyridine binding sites in porcine basilar blood vessels and rat aortic smooth muscle cells.

We examined the interaction of two isomers of S-312, a new calcium channel blocker with a bicyclic dihydrothienopyridine structure, with 1,4-dihydropyridine binding sites. Specific bindings of [3H]nitrendipine and (+)-[3H] PN200-110 in membranes prepared from porcine basilar blood vessels were saturable, reversible, and stereoselective, and had high affinities. The binding properties were very similar to those in membranes from other tissues such as the aorta, myocardium, and cerebral cortex. 1,4-Dihydropyridine calcium channel blockers competed for each radioligand binding in the order of: nisoldipine = nicardipine = S-(+)-S-312 greater than nifedipine greater than R-(-)-S-312. S-(+)-S-312 caused a decrease in the Kd values for both radioligands without changing the maximal binding capacity. 1,4-Dihydropyridines inhibited the high K(+)-induced increase in cytosolic free Ca2+ concentration in rat aortic smooth muscle A7r5 cells. S-(+)-S-312 was 3.3-4.9 times more potent than nicardipine or nisoldipine in inhibiting the Ca2+ increase, although S-(+)-S-312 bound to A7r5 cells with almost the same affinity. These and earlier findings show that S-(+)-S-312 exerts effects more potent than expected from the affinity for [3H]nitrendipine or (+)-[3H]PN200-110 binding sites. This was the case with R-(-)-S-312. These dihydrothienopyridine derivatives appear to interact with the Ca2+ channel in a manner slightly different from the conventional 1,4-dihydropyridines.

Animals↗

PubMed1991

[A clinical survey of advanced bladder cancer: treatment of advanced and non-resectable bladder cancer].

Sixty-three patients with advanced cancer of more than T3b and/or non-resectable bladder cancer who were treated at Kanazawa University Hospital from January 1982 to June 1990 were analyzed with regard to treatment and prognosis. Thirty-one of the 63 patients had non-resectable bladder cancer; T3b in 9, T4b in 15, M1 in 6 and N4 in 4. Twenty-four of the 31 patients received anticancer therapy consisting of systemic chemotherapy, 8 MHz-RF hyperthermia, radiation or a combination of these modalities. With this treatment 9 patients achieved partial response, 4 minor response, 7 no change and 2 progressive disease. In 2 patients evaluation was not performed. Seven of the 31 patients received no treatment. One-year and 2-year survival rates with the above types of treatment were 27.7% and 16.7%, respectively, and 33.4% and 16.7%, respectively, without anti-cancer treatment. There was no significant difference between the survival rates of the two groups. Thirty-two of the 63 patients underwent operation. In 17 patients, total cystectomy was carried out, 9 and 8 of whom received and did not received respectively various adjuvant therapies before operation. One-year and 2-year survivals in the group undergoing adjuvant therapy were 33.3% and 11.1%, respectively, and 66.7% and 66.7% respectively in the group without adjuvant therapy. Survival of the 2 groups did not differ significantly. These data indicate that anticancer treatment including chemotherapy, hyperthermia and radiation dose not enhance long-term survival.

Adult↗

PubMed1991

[End-stage chronic renal failure in patients treated by antireflux operation].

We report 3 patients progressed to end-stage chronic renal failure after antireflux surgery. Preoperatively, the 3 patients had proteinuria, probably due to reflux nephropathy. Surgical procedures used were Paquin's method in 1 patient and Politano-Leadbetter's method in 2. Rapid deterioration of renal function was observed from puberty in all patients. In addition, renal hypoplasia was suspected in 2 patients. We concluded that both reflux nephropathy and renal hypoplasia played important roles in the progression of renal insufficiency.

Adolescent↗

PubMed1990

Enhancement of bradykinin-induced prostacyclin synthesis in porcine aortic endothelial cells by pertussis toxin. Possible implication of lipocortin I.

Bradykinin-stimulated prostacyclin synthesis in porcine aortic endothelial cells was enhanced by pretreatment of the cells with pertussis toxin or islet-activating protein (IAP) for 5 hr or longer. Although ADP-ribosylation of a protein with a molecular weight of 41-42 kD in the cell membranes was completed by 3 hr after the addition of IAP into the incubation medium, there was good correlation between enhancement of bradykinin-induced prostacyclin synthesis and ADP-ribosylation of the IAP substrate over a wide range of IAP concentrations. Furthermore, even if IAP was removed from the incubation medium at 3 hr, bradykinin-induced prostaglandin synthesis at 24 hr was still potentiated. Cycloheximide and actinomycin D enhanced bradykinin-induced prostacyclin synthesis and apparently blocked the effect of IAP. Since this result suggested the involvement of an inhibitor protein(s) of prostacyclin synthesis in the IAP effect, we studied the effect of IAP on the level of lipocortin I which is known to inhibit phospholipase A2. Western and Northern blot analyses revealed that IAP decreased the amounts of protein and mRNA of lipocortin I. These results suggest that the enhancement of bradykinin-induced prostacyclin synthesis by IAP is associated with a decrease in the level of lipocortin I.

Adenosine Diphosphate Ribose↗

PubMed1990

Interaction of lipocortin I with peripheral-type benzodiazepine binding sites.

Recombinant rat lipocortin I increased [3H]PK 11195 binding to porcine aortic smooth muscle membranes, whereas a polyclonal anti-rat lipocortin I antiserum decreased both basal and lipocortin I-enhanced [3H]PK 11195 binding. The results suggest the possibility of lipocortin I being involved in the function of peripheral-type benzodiazepine binding sites.

Animals↗

PubMed1990

Neuropeptide Y receptor in cultured vascular smooth muscle cells: ligand binding and increase in cytosolic free Ca2+.

We have previously shown that neuropeptide Y (NPY) increases cytosolic free Ca2+ concentration [( Ca2+]i) in porcine aortic smooth muscle cells. In this study, specific NPY receptor binding sites were identified in the cells by use of [125I]Bolton-Hunter NPY [( 125I]BH-NPY). Binding was to a single population of the sites with a Kd of 1.1 +/- 0.2 nM and a Bmax of 0.68 +/- 0.10 pmol/mg protein. [125I]BH-NPY binding was displaced by NPY-related peptides including members of the pancreatic polypeptide (PP) family. The potency of these peptides other than human PP for displacing [125I]BH-NPY binding was substantially consistent with their potency for increasing [Ca2+]i. Human PP had no effect on [Ca2+]i even at 10(-5) M, but it inhibited the NPY-induced increase in [Ca2+]i with a potency comparable to that for displacing [125I]BH-NPY binding. NPY(13-36) was about 500 and 300 times less effective than porcine NPY in increasing [Ca2+]i and in displacing [125I]BH-NPY binding, respectively, showing that the NPY receptor in cultured vascular smooth muscle cells is of the Y1-type.

Animals↗

PubMed1989

Neuropeptide Y-induced intracellular Ca2+ increases in vascular smooth muscle cells.

The effect of neuropeptide Y (NPY) on cytosolic free Ca2+ concentration ([Ca2+]i) was studied in cultured smooth muscle cells from porcine aorta (PASMC) and compared with the effect of bradykinin (BK) and angiotensin II (ATII) on [Ca2+]i. All peptides induced dose-dependent and transient rises in [Ca2+]i which were not blocked by extracellular EGTA, but the NPY response was different from the others' as follows. First, the [Ca2+]i rise induced by NPY was not as rapid as that induced by BK or ATII. Second, pertussis toxin abolished the [Ca2+]i rise induced by NPY, but not by BK or ATII. Third, following initial treatment with BK, PASMC were able to respond to NPY, but not to ATII. Finally, BK and ATII, but not NPY, significantly increased inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) generation. Although NPY attenuated forskolin-induced accumulation of cyclic AMP, forskolin- and 3-isobutyl-1-methyl-xanthine-induced alterations in intracellular cyclic AMP did not affect the NPY-induced [Ca2+]i rise. These results suggest that NPY increases [Ca2+]i by a pertussis toxin-sensitive GTP binding protein-involved mechanism which is not mediated by the intracellular messengers such as Ins(1,4,5)P3 and cyclic AMP.

1-Methyl-3-isobutylxanthine↗

PubMed1989

Antagonistic actions of S-145 on vascular and platelet thromboxane A2 receptors.

We studied the actions of a potent thromboxane A2/prostaglandin in H2 (TP) receptor antagonist, (+/-)-(5Z)-7-[3-endo-[(phenylsulfonyl)amino]bicyclo [2.2.1]hept-2-exo-yl]heptenoic acid (S-145) on vascular and platelet receptors in the pig. S-145 showed almost the same affinity for both receptors in ligand binding studies with [3H]U46619 or [3H]SQ29, 548. The binding affinity of S-145 was 5-8 times higher than that of SQ29,548, a well-characterized TP receptor antagonist. However, S-145 inhibited U46619-induced contractions of pig coronary arteries with an IC50 value 52.5 times lower than that of SQ29,548, and was approximately equipotent with SQ29,548 in inhibiting U46619-induced secondary aggregation of pig platelets. Detailed kinetic studies on [3H]S-145 binding revealed that the apparent discrepancy between the pharmacological potency of S-145 in platelet and vascular systems was not due to tissue selectivity, but its small association constants for both receptors.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1989

Comparison of vascular and platelet thromboxane A2/prostaglandin H2 receptors in the pig.

We compared the properties of vascular and platelet thromboxane A2/prostaglandin H2 receptors in the pig. The binding profiles of U46619, several prostaglandins and thromboxane A2/prostaglandin H2 receptor antagonists to the aorta and platelet receptors were almost the same irrespective of whether the agonist ([3H]U46619) or the antagonist ([3H]SQ29,548) radioligand was used, except that the receptor density in the latter was 4 times higher than that in the aorta. The antagonists suppressed U46619-induced contraction of pig coronary artery and secondary aggregation of platelets at potencies comparable to their KI values in the binding experiments. On the other hand, the responses of the artery specimens to U46619 and the prostaglandins differed from those of the platelets. Thus, the binding sites in the vascular and platelet receptors seem to be the same or quite similar, but there seem to be different mechanism(s) leading the agonistic binding signal to final responses.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1989

High-affinity binding sites for PK 11195, but not for RO5-4864, in porcine aortic smooth muscle.

Peripheral benzodiazepine (BZ) binding sites were characterized in porcine aortic smooth muscle membrane preparation. [3H]PK11195 bound with high affinity to the membranes (Kd = 8.6 + 0.9 nM), whereas [3H]Ro5-4864 bound slightly to the membranes. The Ki value of Ro5-4864 obtained from the inhibition of [3H]PK 11195 binding was 1200 + 200 nM, which was 480 times weaker than that obtained in rat kidney. Furthermore, the Ro5-4864 effect was temperature-insensitive. When [3H]PK 11195 binding was examined in porcine, human and rat platelets, Ro5-4864 inhibited the binding in porcine and human platelets one order of magnitude less potently than that in rat platelets. These results suggest that low affinity for Ro5-4864 in porcine aorta smooth muscle originates in porcine tissue, but not in smooth muscle.

Animals↗

PubMed1989

Muscarinic excitation and inhibition of neurons in the submucous plexus of the guinea-pig caecum.

Intracellular recordings were made from neurons in the submucous plexus of the guinea-pig caecum. Muscarinic agonists (acetylcholine, bethanechol and muscarine) depolarized about 70%, and hyperpolarized about 30% of the submucous plexus neurons. Low concentrations of pirenzepine reversibly antagonized both responses. The measured dissociation constants (KD) of 10-30 nM for the depolarizations and 1-3 nM for the hyperpolarizations suggest that each response was mediated by muscarinic M1 cholinoceptors. The muscarinic depolarization and hyperpolarization were associated with a decreased and an increased conductance, respectively, and the reversal potential for the muscarinic responses varied as the potassium concentration varied, always being around the potassium equilibrium potential. In cells depolarized by muscarinic agonists these agents appeared to decrease a potassium conductance that could also be inactivated by substance P. In approximately 30% of the submucous neurons, the slow inhibitory postsynaptic potential, elicited in response to single or repetitive focal stimuli (1-10 pulses at 20-40 Hz), appeared to consist of a large component which was sensitive to the blocking action of idazoxan (100-300 nM) and a small component which was idazoxan-insensitive. The latter (muscarinic slow inhibitory postsynaptic potential) was completely abolished by pirenzepine. The concentrations of pirenzepine which caused a 50% depression ranged from 5 to 20 nM. The muscarinic slow inhibitory postsynaptic potential was increased in amplitude and duration by physostigmine (100-300 nM). The muscarinic slow inhibitory postsynaptic potential was accompanied by a decrease in membrane input resistance, and was reversed in polarity near the potassium equilibrium potential. When muscarine induced a hyperpolarization and/or focal stimulation elicited a muscarinic slow inhibitory postsynaptic potential in the presence of idazoxan (100-300 nM), the intracellular injection of guanosine 5'-O-(3-thiotriphosphate) produced a progressive membrane hyperpolarization during which the muscarinic hyperpolarizing responses were attenuated. It is concluded that the muscarine-induced reduction in potassium conductance is mediated through a muscarinic M1 receptor which has a relatively low affinity for pirenzepine. The muscarine-induced increase in potassium conductance is probably produced by the association of a guanine nucleotide-binding regulatory protein with another muscarinic M1 receptor that has a relatively high affinity for pirenzepine.

Acetylcholine↗

PubMed1988

Characterization of [3H]U46619 binding in pig aorta smooth muscle membranes.

The binding characteristics of [3H]U46619, a tritiated thromboxane A2/prostaglandin H2 mimetic, were studied in pig aorta smooth muscle membranes. Binding was fast, saturable, selective and reversible. The KD values determined by kinetics, equilibrium binding and drug competition methods were 68, 42 and 53 nM, respectively. The Bmax was 87.8 fmol/mg protein. Specific binding was competitively displaced by thromboxane A2/prostaglandin H2 antagonists. Binding was also displaced by prostaglandins D2, E2 and F2 alpha with IC50 values of 8, 21 and 12 microM, respectively. U46619 contracted the rat and pig aorta smooth muscle, but the response of the latter was slower than that of the former. The antagonists prevented the U46619-induced contraction of rat aorta with the same rank order as that for the inhibition of ligand binding in pig aorta smooth muscle membranes. These results provide evidence that the putative thromboxane A2/prostaglandin H2 receptor in vascular smooth muscle membranes can be detected by a ligand binding technique.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗