Biomedical subjects

T Masaki

Publications and source records attributed to T Masaki.

At least 253 records · Page 14Linked to original sources

PubMed1995

Human factor H and C4b-binding protein serve as factor I-cofactors both encompassing inactivation of C3b and C4b.

Human factor H in the complement (C) system has been characterized as a decay-accelerator for the alternative C pathway C3 convertase and a cofactor for factor I-mediated inactivation of C3b. The current concept is that it does not serve as a C4b-inactivating cofactor. In the present study, we demonstrated that in fluid-phase, factor H and Factor I can cleave methylamine-treated C4(C4ma), a C4b analogue, to C4d, regardless of its isotype. The buffer pH and ionic strength were critical factors for the C4ma cleavage, which proceeded at around pH 6.0 and low conductivity around 3.0 mS. Similar results were obtained with fluid-phase C4b. Cell-bound C4b, however, did not undergo factor I-mediated inactivation by factor H. Hence, all of the human cofactors reported to date can mediate factor I-mediated cleavage of both C3b and C4b at least in the fluid-phase.

Carrier Proteins↗

PubMed1995

Endothelin-1 and endothelin B type receptor are induced in mesangial proliferative nephritis in the rat.

We studied whether endothelin-1 (ET-1) and its receptor subtypes (ETAR, endothelin A type receptor; and ETBR, B type receptor) were up-regulated in the glomerulus of a rat model of mesangial proliferative glomerulonephritis induced by anti-thymocyte serum (anti-Thy-1 GN). A marked increase in preproET-1 mRNA could be demonstrated in glomerular RNA 3 and six days after disease induction (4.1- and 4.9-fold vs. day 0, respectively), corresponding to the time of mesangial cell proliferation, to the time of macrophage infiltration into glomeruli, and also to the time of increase in glomerular PDGF B-chain mRNA expression. The localization of ET-1 protein in the mesangial area and along the inner aspect of the glomerular capillary wall was also demonstrated by immunohistochemistry from day 3 and maximal at day 6. The major source of the cells expressing ET-1 in glomeruli appeared to be mesangial cells, glomerular endothelial cells and monocyte/macrophages. Furthermore, both gene and protein expression of ET-1 were associated with increased urinary excretion of ET-1. There was no increase in the plasma ET-1 immunoreactivity. Glomerular expression of ETBR mRNA increased in anti-Thy-1 GN (1.5-fold vs. day 0 at day 3 after disease induction, 3.6-fold at day 6 and 2.7-fold at day 10), but there was minimal change in ETAR mRNA expression. These results suggest that preproET-1 mRNA, which is induced in anti-Thy-1 GN, is linked primarily with ETBR mRNA expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Characterization of a dopamine-releasing action of 6R-L-erythro-tetrahydrobiopterin: comparison with a 6S-form.

6R-L-erythro-Tetrahydrobiopterin (6R-BH4) is a cofactor for aromatic L-amino acid hydroxylases and nitric oxide synthase. Recently, we have reported that independently of its cofactor activities, 6R-BH4 acts from the outside of neurons in the brain to enhance the release of monoamine neurotransmitters such as dopamine. To characterize the pharmacological properties of the action, we examined the effects of 6S-BH4, a diastereoisomer of 6R-BH4, on dopamine release in the rat striatum by using brain microdialysis and compared its effects with those of 6R-BH4. Perfusion of 6S-BH4 or 6R-BH4 through the dialysis probe increased extracellular dopamine levels (an index of in vivo dopamine release) concentration dependently; the maximal increase by 6S-BH4, was one-sixth of that by 6R-BH4. 6S-BH4 increased extracellular DOPA levels in the presence of NSD 1015, an inhibitor of aromatic L-amino acid decarboxylase (an index of in vivo tyrosine hydroxylase activity), to an extent similar to the increase induced by 6R-BH4. The increase in the DOPA levels induced by either of the pteridines was abolished after pretreatment of rats with alpha-methyl-p-tyrosine (an inhibitor of tyrosine hydroxylase). Under the same conditions, the 6S-BH4-induced dopamine release was abolished, but most of the 6R-BH4-induced increase persisted. Coadministration of 6S-BH4 with 6R-BH4 inhibited the increase in dopamine release induced by 6R-BH4 alone. These results show that 6R-BH4 stimulates dopamine release by acting at the specific recognition site on the neuronal membrane, and that 6S-BH4 acts as an antagonist of 6R-BH4 at this site, although it has cofactor activities.

Animals↗

PubMed1995

Long-lasting activation of cation current by low concentration of endothelin-1 in mouse fibroblasts and smooth muscle cells of rabbit aorta.

1. Recombinant human ETA receptors were expressed in a mouse fibroblast cell line (Ltk- cell) and functional coupling of the receptors with Ca2+ permeable channels at low concentrations of endothelin-1 (ET-1) was investigated using whole-cell recordings and monitoring the changes in intracellular free Ca2+ concentrations ([Ca2+]i) with a Ca2+ indicator, fluo-3. A similar type of coupling was investigated in freshly dispersed vascular smooth muscle cells (VSMCs) of rabbit thoracic aorta by use of whole-cell recordings. 2. In Ltk- cells expressing recombinant human ETA receptors, concentrations of ET-1 (10(-8) M, 10(-9) M) evoked an initial transient peak and a subsequent sustained elevation in [Ca2+]i whereas a lower concentration of ET-1 (10(-10) M) evoked only a sustained elevation of [Ca2+]i. After removal of extracellular Ca2+, ET-1 evoked only an initial peak without a sustained elevation of [Ca2+]i. The sustained elevation induced by 10(-10) M ET-1 was blocked by 300 microM mefenamic acid (a cation channel blocker) but not by 10 microM nifedipine (a blocker of voltage-operated Ca2+ channel). 3. In whole-cell recordings with Ltk- cells, a brief (3-5 min) application of ET-1 (10(-10) M) induced a sustained inward current at a holding potential of -60 mV. The current-voltage relationship revealed that the reversal potential of the ET-1-induced current was close to 0 mV (1.9 mV) and was not altered by reducing the concentration of Cl- in the bath solution, indicating that the current is carried by cations. The current was reversibly blocked by 300 microM mefenamic acid, and it persisted after all cations in the bath solution had been replaced by Ca2+ (5 or 30 mM) and nonpermeant cation N-methyl-D glucamine,indicating that the ET-1-activated channel is permeable to Ca2+. Activation of the current was independent of membrane potential and the current was induced even after addition of a high concentration (10 mM) of a Ca2+ chelator, EGTA, to the pipette solution.4. In whole-cell recordings from rabbit aortic VSMCs, ET-l (101-10 M) induced a sustained inward current at a holding potential of -60 mV. The reversal potential was - 12 mV and was not altered when the concentration of Cl- in the pipette solution was decreased, indicating that the current is carried by cations. Again activation of the current was independent of membrane potential and was observed even after addition of a high concentration (10 mM) of a Ca2+ chelator, EGTA to the pipette solution. The current was reversibly blocked by 300 microM mefenamic acid and was permeable to Ca2+,showing marked similarities to ET-1-induced cationic current in Ltk- cells.5. These results indicate that in Ltk- cells transfected with cDNA for recombinant ETA receptors andVSMCs, ETA receptors can functionally couple with a nonselective cation channel permeable to Ca2+.Thus the present data suggest that the cation channel plays an essential role in the sustained elevation of[Ca2+]i at low concentrations of ET-l by causing Ca2+ entry through the channel.

Aniline Compounds↗

PubMed1995

The quest for a more acceptable bowel preparation: comparison of a polyethylene glycol/electrolyte solution and a mannitol/Picolax mixture for colonoscopy.

Eighty-nine consecutive patients attending for day-case colonoscopy were randomly allocated either polyethylene glycol/balanced electrolyte (PEG) mixture (n = 45) or a mannitol/Picolax mixture (n = 44). Both preparations were administered in two fractions. Patients recorded their experience of the preparation on a questionnaire and one of two experienced endoscopists (unaware of the type of preparation given) assessed the result of bowel cleansing. Carbon dioxide insufflation was used for all examinations. Good/excellent bowel cleansing occurred in significantly more patients given PEG, 43 (96%), than those allocated mannitol/Picolax, 34 (77%), p = 0.01. More patients receiving mannitol/Picolax were able to complete the preparation in full than patients receiving PEG (38 vs 27, p = 0.01). More patients found the taste of mannitol/Picolax pleasant compared to PEG (46% vs 20%). Both preparations had a similar side-effect profile. Of those patients tested, 13% receiving mannitol/Picolax had a postural drop in blood pressure and blood parameters suggestive of mild dehydration. A fractionated administration of PEG as a bowel preparation for day-case colonoscopy is well tolerated and superior as a cleansing agent to a mannitol/Picolax combination. Provided carbon dioxide is used as the insufflating agent, mannitol/Picolax is an acceptable alternative in fit, young patients intolerant of PEG.

Administration, Oral↗

PubMed1995

Possible role of endothelin in endothelial regulation of vascular tone.

In vascular beds, a potent vasoconstrictor of endothelin-1 (ET-1) is produced by endothelial cells and released preferentially to the basal side of endothelial cells. It acts on endothelial cells and on the underlying smooth muscle cells, as a modulator of vascular tone, in an autocrine and paracine manner. ET-1 induces release of relaxing factors (nitric oxide and prostacycline) from endothelial cells. Whether relaxation or constriction is predominantly elicited by endogenous ET-1 may depend on the concentration of ET-1 in vascular beds, the density and mode of distribution of ET receptor subtypes on the endothelial and smooth muscle cells, the turnover of the receptors, and the existing conditions of each vascular beds. When ET-1 is overproduced by endothelial cells at pathological conditions, endogenous ET-1 acts as a vasoconstrictor. However, ET-1 may act as a vasodilator at physiologically low concentrations, depending on the existing condition.

Amino Acid Sequence↗

PubMed1995

Negative chronotropic effect of endothelin 1 mediated through ETA receptors in guinea pig atria.

Endothelins exert potent excitatory cardiac effects by acting on specific receptors on myocytes. In this study, we have examined the signal transduction mechanism for the chronotropic effect of endothelins in guinea pig atria. A competition binding of [125I]endothelin 1 ([125I]ET-1) using the recently developed ETA receptor-selective antagonist BQ123 showed the presence of almost equal populations of ETA (44%) and ETB (56%) receptors in the guinea pig right atria. In a concentration-response study, endothelin 3 (ET-3), an agonist with higher affinity to ETB receptors than to ETA receptors, and sarafotoxin S6c (STXS6c), an ETB receptor-selective agonist, increased the rate of spontaneous beating at all concentrations tested (10 pmol/L to 100 nmol/L). In contrast, ET-1, a nonselective agonist, increased the heart rate at lower concentrations (10 pmol/L to 10 nmol/L) but decreased it at higher concentrations (30 to 100 nmol/L). When ET-1 (100 nmol/L) was applied in a single amount, heart rate was strongly increased; however, this increase was followed by a rapid decline in the response. ET-1 (100 nmol/L) but not ET-3 or STXS6c significantly reduced the heart rate when it was raised by isoproterenol (ISO, 300 nmol/L) either in the absence or presence of a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). Correspondingly, ET-1 significantly reduced the ISO-induced elevation of cAMP accumulation (19.1 +/- 1.7 pmol/mg protein [n = 8] and 12.6 +/- 1.2 pmol/mg protein [n = 7] in the absence and presence of ET-1, respectively; P < .01), which was also observed even in the presence of IBMX.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Suppression of endothelin-1-induced mitogenic responses of human aortic smooth muscle cells by interleukin-1 beta.

When applied to quiescent human aortic smooth muscle cells (AOSMC), endothelin-1 (ET-1) caused significant increases in mitogen-activated protein kinase (MAPK) activity, [3H]thymidine incorporation, and cell proliferation, confirming an activity of ET-1 as a potent mitogen on AOSMC. As an in vitro model to evaluate the significance of the mitogenic activity of ET-1 on smooth muscle cells during atherogenesis, we studied possible modulations of the responsiveness of the cells by treatment with various cytokines (IL-1 beta, IL-8, TNF alpha, and TGF beta). Of the four cytokines tested, we found that the treatment of the cells with IL-1 beta dramatically reduced the responsiveness of the cells to ET-1; IL-1 beta treatment at the concentration of 0.2 ng/ml for 8 h completely abolished the activity of ET-1 to induce the mitogenic responses. IL-1 beta treatment caused no changes in the responses induced by EGF, basic fibroblast growth factor, or PDGF. Studies on ET-1-induced intracellular signaling events in IL-1 beta-treated cells revealed that the failure of ET-1 to induce mitogenic responses was due to an increase in cAMP formation secondary to ET-1-induced activation of prostanoid metabolism. These findings on AOSMC in vitro raise the possibility that, under some inflammatory conditions in vivo, ETs may work as a negative modulator of smooth muscle cell proliferation.

Amino Acid Sequence↗

PubMed1995

Renal glomerular fibrosis in two pigs.

Massive deposition of collagen fibrils was found in the renal glomeruli of two pigs. The affected pigs were a 6-month-old female hybrid pig with systemic mycobacteriosis and a retired sow showing azotemia. Microscopically, various amounts of a homogeneous eosinophilic substance were deposited within the expanded mesangium of almost all renal glomeruli in both cases. The deposit was also seen occasionally on the glomerular capillary walls in the sow. Capillary lumens were occluded in the glomerular segments with heavy deposition. Obsolescent glomeruli were often surrounded by lymphoid cells. The deposited substance was Congo red negative and stained deep blue with Heidenhain's azan staining. Immunohistochemical evaluation revealed that the major component of the homogeneous substance was type-III collagen. Electron microscopic examination showed that the deposits were masses of fibrils of variable length, width, and shape. The fibrils had transverse bands with a periodicity of approximately 60 nm, consistent with collagen fibrils. These glomerular changes were identical to those of collagenofibrotic glomerulonephropathy that has recently been described as a new glomerular disease in humans. The glomerular lesion may be the result of unusual production of type-III collagen by mesangial cells.

Animals↗

PubMed1995

Involvement of annexin-I in glucose-induced insulin secretion in rat pancreatic islets.

Annexin-I was demonstrated to specifically present in islets and not in exocrine tissues of the rat pancreas and to have a diffuse and homogeneous distribution in all islet cells in our previous study. In the present report, to clarify the functions of annexin-I in rat pancreatic islets, especially in beta-cells, we investigated the role of annexin-I in insulin secretion. Immunoelectron microscopic analysis of pancreatic beta-cells demonstrated that immunogold particles reactive to annexin-I were almost exclusively observed on most of the insulin-containing granules (approximately 90%) and less frequently located in cytosol and other organelles, such as the endoplasmic reticulum and mitochondria. The number of annexin-I gold particles located on insulin granules after oral glucose administration was significantly increased compared with that observed in fasted rats. Moreover, when the isolated islets were stimulated by a high concentration of glucose (20 mM), the phosphorylation of annexin-I was markedly enhanced, and it was synchronized to insulin secretion. This phosphorylation mainly occurred on serine residues. H-7 (100 microM), a potent inhibitor of protein kinase-C, inhibited the phosphorylation to about 90%. These findings suggest that annexin-I might be involved in the regulatory mechanism of glucose-induced insulin secretion in rat pancreatic islets via phosphorylation-dephosphorylation processes.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1995

[Mutagenesis study of pharmacological receptors: approach to their structure-function relationships].

Recent cDNA cloning of pharmacological receptors revealed their primary structures, and the following functional studies with those cloned receptors enabled us to discover the existence of various receptor subtypes. Each receptor has three characteristics properties: 1) ligand binding, 2) effector coupling and 3) desensitization. Delineation of precise domains of a receptors involved in these functions is now an important matter. The molecular mapping of receptors would give us not only a rationale for designing selective drugs, but also new insight about the genotype-phenotype relationships of a certain kinds of hereditary diseases caused by a mutation of receptor genes. A mutagenesis study is a powerful approach for elucidating the structure-function relationships of pharmacological receptors. In contrast to a peptide, a protein is impossible to engineer in vitro. However, modulation of a specific codon in a given cDNA could bring about a substitution of a corresponding amino acid in the protein expressed in vivo. In this article, the popular strategies for generating artificially mutated receptors are discussed. This review will focus on three types of mutant receptors: 1) point mutation, 2) chimeric and 3) truncated receptors. The annotated bibliographies will also come in handy when devising experimental protocols.

Animals↗

PubMed1995

Two different endothelin B receptor subtypes mediate contraction of the rabbit saphenous vein.

To study endothelin receptor subtypes that mediate venous smooth muscle contraction, effects of some endothelin receptor agonists and antagonists on the rabbit lateral saphenous vein were examined and compared with those on the saphenous artery. In the artery, endothelin (ET)-1 elicited concentration-dependent contractions, while selective ETB-receptor agonists, IRL1620 (Suc-[Glu9,Ala11,15]ET-1(8-21)) and sarafotoxin 6c (S6c) had almost no effect. The ET-1-induced responses shifted in parallel to the right by BQ-123 (cyclo (-D-Trp-D-Asp-Pro-D-Val-Leu-)), an ETA-receptor antagonist, or PD142893 (Ac-D-Dip-Leu-Asp-Ile-Ile-Trp), an ETA/ETB-receptor antagonist, indicating the involvement of the ETA receptor in this response. In the saphenous vein, not only ET-1 and ET-3, but also ETB-receptor agonists, IRL1620, S6c and [Glu9]sarafotoxin 6b ([Glu9]S6b), produced concentration-dependent, BQ-123-insensitive contractions. PD142893 did not affect the ET-1-induced contraction, but it shifted greatly the IRL1620-induced concentration-response curve in parallel to the right. The major components of ET-3-, S6c- and [Glu9]S6b-induced contractions were resistant to PD142893. These results indicate that two different vasoconstrictive ETB-receptor subtypes, ETB1 (sensitive to IRL1620 and PD142893) and ETB2 (insensitive to IRL1620 and PD142893), are located on the smooth muscle of the saphenous vein.

Animals↗

PubMed1995

Pharmacological heterogeneity of both endothelin ETA- and ETB-receptors in the human saphenous vein.

To study endothelin receptor subtypes that mediate the smooth muscle contraction of human saphenous vein, effects of some endothelin-receptor agonists and antagonists were examined. Endothelin (ET)-1 and sarafotoxin 6b (S6b) elicited potent concentration-dependent contractions with similar pD2 values and similar maximal responses. Selective ETB-receptor agonists, sarafotoxin 6c (S6c) and IRL1620 (Suc-[Glu9,Ala11,15]-endothelin-1(8-21)), also caused contractions, but their maximal responses were about one third of that of ET-1. ET-3 showed a biphasic concentration-response curve. An ETA-receptor antagonist, BQ-123 (cyclo(-D-Asp-L-Pro-D-Val-L-Leu-D-Trp-)), an ETA/ETB-receptor antagonist, PD142893 (Ac-D-Dip-Leu-Asp-Ile-Ile-Trp), or the combination of these two antagonists hardly affected the contractile effect of ET-1, while each of them markedly antagonized the effects of higher concentrations of ET-3 and S6b. Contractions induced by lower concentrations of ET-3 and S6b were resistant to these antagonists. The concentration-response curves for S6c and IRL1620 were not affected by BQ-123. The effect of IRL1620 was markedly inhibited by PD142893, while S6c-induced contractions were much more resistant to PD142893. These different sensitivities to antagonists suggested heterogeneity of both ETA- and ETB-receptors [ETA1 (sensitive to BQ-123), ETA2 (resistant to BQ-123), ETB1 (sensitive to PD142893) and ETB2 (resistant to PD142893)] in the human saphenous vein, although contractions mediated by ETB-subtypes have smaller maximal responses than those mediated by the ETA-subtypes.

Dose-Response Relationship, Drug↗

PubMed1995

Modulation of glomerular endothelin and endothelin receptor gene expression in aminonucleoside-induced nephrosis.

This study assessed glomerular endothelin (ET)-1, ET-3, and ET-receptor A and B mRNA levels in puromycin aminonucleoside (PAN)-induced nephrosis. During the nephrotic stage, 8 days after PAN injection, ET-1 and ETB receptor mRNA were elevated by 2.8 +/- 0.8-fold (P < 0.01) and 2.4 +/- 0.9-fold (P < 0.01), respectively, as compared with controls. These mRNA levels decreased to control levels by Day 20, when the nephrosis was in remission. In contrast, glomerular ETA receptor mRNA levels did not change in PAN nephrosis or control rats during the experimental period. ET-3 mRNA was not detected in the glomeruli of PAN nephrosis or control rats. Additionally, plasma ET concentration and glomerular ET production were measured in PAN nephrosis and control rats by radio-immunoassay. Eight days after PAN injection, ET-1 levels in plasma and glomeruli were not significantly altered in rats with PAN-induced nephrosis (glomeruli, 104.68 +/- 16.46 pg/mg of protein versus 98.24 +/- 13.68 pg/mg of protein; plasma, 2.68 +/- 1.10 versus 2.52 +/- 0.98 pg/mL). The administration of methylprednisolone to PAN rats resulted in the rapid disappearance of proteinuria and partially attenuated the increased ET-1 and ETB receptor gene expression in the glomeruli. These data indicate that glomerular ET-1 and ETB receptor expression in PAN nephrosis in increased at the mRNA level and that methylprednisolone treatment results in an attenuated increase.

Animals↗

PubMed1995

[Endoscopic treatment of colorectal cancer].

Endoscopic polypectomy should be applied only for early colorectal carcinomas. Intramucosal carcinoma do not have a risk of lymph node metastases. However, there is an about 10% risk of lymph node metastases among carcinomas showing submucosal invasion (sm carcinoma). When risk factors revealed to be positive after polypectomy, subsequent surgical resection of the large bowel with lymph nodes dissection is needed, because these sm carcinomas are considered to have a high risk of lymph node metastases. Therefore, accurate diagnosis of depth of invasion is essential to prevent subsequent surgical resection following endoscopic polypectomy. Endoscopy, barium enema and endoscopic ultrasonography (EUS) are all considered to be effective for an accurate diagnosis of depth of invasion. Endoscopic polypectomy includes hot biopsy, snare polypectomy and endoscopic mucosal resection (EMR). Appropriate maneuver must be chosen, considering the characteristics of the lesion. Major complications after endoscopic polypectomy are bleeding and perforation of the large bowel. Including an establishment of a new risk factors, further efforts must be made to prevent unnecessary additional surgical resection of the large bowel following endoscopic polypectomy.

Aged↗

PubMed1995

Renal osteodystrophy in hemodialysis patients.

Patterns of bone loss in the axial and appendicular skeleton were studied in 88 chronic hemodialysis patients (59 males and 29 females) and 60 normal volunteers (30 males and 30 females). The hemodialysis patients were properly medicated with phosphate binders and 1 alpha-OH D3 where necessary. The metacarpal index (MCI), sigma gray scale/diameter (sigma GS/D) and bone mineral content (BMC) were measured as bone mass indices, and the relationship investigated between clinical factors [age, duration of hemodialysis, serum phosphate (P), calcium (Ca), carboxy-terminal fragments of parathyroid hormone (C-PTH), osteocalcin (OC), alkaline phosphate (ALP) and Ca x P]. The bone loss in the hemodialysis patients was greater than that in the normal controls and was accelerated after menopause in women. However, the bone mass indices in a few of the hemodialysis patients of advanced age (over 60) showed higher values than those of the controls. The bone mass indices in male hemodialysis patients showed a negative correlation with the hemodialysis duration, C-PTH and OC, as did those in female patients with hemodialysis duration. On the other hand, BMC in female hemodialysis patients showed a negative correlation with P, C-PTH and Ca x P. In conclusion, age and the duration of hemodialysis are the most essential factors in skeletal and trabecular bone loss in male and female hemodialysis patients. Subsequent factors responsible for skeletal bone loss in male patients are C-PTH and OC, and those for trabecular bone loss in female patients are P, C-PTH and Ca x P. Control of the levels of C-PTH, OC, P and Ca x P is recommended for prevention of bone loss in hemodialysis patients.

Adult↗

PubMed1995

Distinct roles of second and third intracellular loops of human endothelin receptors in the selective activation of G alpha s/G alpha i.

Endothelin-1 (ET-1) stimulated cAMP formation in Chinese hamster ovary cells stably expressing human wild-type ET(A) (CHO/hET(A) cells) and inhibited the formation in cells expressing human wild-type ETB (CHO/hETB cells), suggesting a selective coupling of hET(A) and hETB with G alpha s and G alpha i, respectively. To find out the receptor domain(s) that determined the selective coupling, a series of chimeric receptors between hET(A) and hETB were expressed on CHO cells and the effect of ET-1 on cAMP formation in each cell line was tested. hET(A) with the replacement of the second and/or third intracellular loop (ICLII and/or III) to the corresponding region(s) of hETB failed to transmit the stimulatory effect of ET-1. hETB with the replacement of ICLIII to the corresponding region of hET(A) failed to transmit the inhibitory effect of ET-1. A chimeric receptor with ICLII of hETB and with ICLIII of hET(A) failed to transmit either effect. These results indicated the roles of ICLII and III of hETR as major determinants of the selective coupling of hET(A)/hETB with G alpha s/G alpha i, respectively.

Animals↗

PubMed1995

Functional coupling of ETA receptor with Ca(2+)-permeable nonselective cation channel in mouse fibroblasts and rabbit aortic smooth-muscle cells.

Endothelin-1 (ET-1) induces persistent vasoconstriction via a sustained increase in intracellular free Ca2+ concentrations ([Ca2+]i). The mechanisms of the elevation of [Ca2+]i operating at physiologically low concentrations of ET-1 are controversial. Here we report that both native ETA receptors in vascular smooth-muscle cells and recombinant ET(A) receptors expressed in mouse fibroblasts (Ltk cells) are functionally coupled with a non-selective cation channel, which is permeable to Ca2+ and is blocked by mefenamic acid. The channel is persistently activated by a low concentration of ET-1 (10(-10) M) without stimulation of inositol triphosphate (IP3) formation and mediates sustained vasoconstriction.

Animals↗