Biomedical subjects

J Kawabe

Publications and source records attributed to J Kawabe.

At least 55 records · Page 3Linked to original sources

PubMed1997

Isoform-dependent activation of adenylyl cyclase by proteolysis.

Recent findings have suggested that the cellular proteolytic system plays a major role in the regulation of various intra- and extra-cellular signaling. It was previously shown that proteolytic treatment of adenylyl cyclase leads to the activation of this enzyme. We demonstrate that this activation occurs in an adenylyl cyclase isoform-dependent manner. The type II isoform was strongly activated (approximately 500%), the type III isoform was modestly activated (approximately 30%),and the type V isoform was inhibited by trypsin. Activation of type II adenylyl cyclase occurred in trypsin dose- and time-dependent manners and was blocked by a trypsin inhibitor in a dose-dependent manner. Other proteases, such as thrombin and plasminogen, similarly activated the type II isoform, but not the others. Our data suggest that proteolytic activation is an isoform- and thus cell type-dependent mechanism of altering adenylyl cyclase catalytic activity.

Adenylyl Cyclases↗

PubMed1997

Isoform-specific regulation of adenylyl cyclase by oxidized catecholamines.

Both epinephrine and manganese are known to stimulate cAMP production in cardiac homogenates. When added together, however, they inhibited adenylyl cyclase catalytic activity. Type V adenylyl cyclase, the major isoform in the heart, was also inhibited when an increasing concentration of epinephrine was added in the presence of manganese. Inhibition was not dependent on the condition of stimulation or preparation of the enzyme. However, this inhibition was abolished in the presence of anti-oxidant. Other catecholamines, including dopamine and isoproterenol, as well as adrenochrome, an oxidized product of epinephrine, similarly inhibited the activity of this enzyme. Kinetic analyses revealed that the K(m) for the substrate ATP was unchanged, but the V(max) was significantly decreased. In contrast, type II adenylyl cyclase, a non-cardiac isoform, was resistant to such inhibition by adrenochrome and was somewhat stimulated by it. Thus, catecholamines, when oxidized, directly interacted with adenylyl cyclase in an isoform-specific manner in the absence of G proteins. Our findings suggest that adenylyl cyclase isoforms have different sensitivity to various stresses, including oxidative stress.

Adenylyl Cyclases↗

PubMed1997

[Secretion of atrial natriuretic peptide from the left ventricle and heart in patients with hypertrophic cardiomyopathy: relationship with hemodynamic and echocardiographic profiles].

This study investigated whether atrial natriuretic peptide (ANP) secretion from the left ventricle occurs and correlated any secretion with the hemodynamic or echocardiographic parameters in patients with hypertrophic non-obstructive cardiomyopathy (HNCM). Volume overload was induced by intravenous injection of low-molecular weight dextran in 19 patients with HNCM and seven normal subjects (control group). Simultaneous measurements of plasma ANP concentrations in the aortic root, anterior interventricular vein and coronary sinus, and hemodynamic parameters were performed before and after volume overload. Echocardiographic parameters were measured under the basal conditions in the HNCM group. There was no difference in ANP concentrations between the aorta and anterior interventricular vein either before or after volume overload in the control group, whereas they were significantly higher in the anterior interventricular vein than in the aorta both before and after volume overload in the HNCM group, suggesting increased ANP secretion from the left ventricle. Moreover, the difference in ANP concentrations between these locations was enhanced by volume overload. In the HNCM group, the differences in ANP concentrations between these locations were positively correlated with the pulmonary capillary wedge pressure and left ventricular end-diastolic pressure before and after volume overload, but not with left ventricular thickness or left atrial dimension. These results suggest that enhanced ANP secretion from the left ventricle in both basal and volume overloaded states occurs in HNCM, and this ANP secretion from the left ventricle is closely related to left ventricular end-diastolic pressure but not to wall thickness and mass index of left ventricle.

Aorta↗

PubMed1997

[A case of an adult neuroblastoma with bone-marrow metastases: 131I-MIBG scintigraphy in comparison with MRI].

To detect a primary neuroblastoma lesion and its metastases, 131I-MIBG scintigraphy was performed for a 24-year-old woman who had a high level of serum catecholamine. 131I-MIBG scintigrams showed high radioactivity in the left upper quadrant, pelvic bone, and vertebral bodies. A biopsy of the pelvic bone revealed metastasis from the neuroblastoma. After four chemotherapy courses, the accumulation of 131I-MIBG decreased after each course; however, scintigraphy performed after the last chemotherapy course showed focal mild uptake in the right sacroiliac. The presence of residual tumor in the sacroiliac was confirmed histologically. On the other hand, T1-weighted and T2-weighted MR images performed before the treatment showed low signal intensity and high signal intensity in the pelvic bone, respectively. After the fourth chemotherapy course, T2-weighted MR images showed low signal intensity in the pelvic bone; however, it was difficult to determinate whether it should improve. To assess the effect of treatment of neuroblastoma, 131I-MIBG scintigraphy was considered more useful than MRI.

3-Iodobenzylguanidine↗

PubMed1995

Regulation of adenylyl cyclase by protein kinase A.

The changing relationship between stimuli and responses after prolonged receptor stimulation is a general feature of hormonal signaling systems, termed desensitization. This phenomenon has been best exemplified in the covalent modification of the G protein-linked catecholamine receptors. However, other components within this signaling pathway can be involved in desensitization. Here we present evidence that desensitization occurs at the level of the effector enzyme itself through phosphorylation. Type V adenylyl cyclase (AC) is the major isoform expressed in the heart. Using purified enzymes, we demonstrate that protein kinase A (PKA) directly phosphorylates and thereby inhibits type V AC catalytic activity. This inhibition was negated in the presence of PKA inhibitor. Analysis of enzyme kinetics revealed that this inhibition was due to a decrease in the catalytic rate, not to a decrease in the affinity for the substrate ATP. Our results indicate that AC catalytic activity can be regulated through PKA-mediated phosphorylation, suggesting another mechanism of desensitization for receptor pathways which signal via increases in intracellular cAMP.

Adenosine Triphosphate↗

PubMed1995

Multiplicity in type V adenylylcyclase: type V-a and type V-b.

Type V mammalian adenylylcyclase cDNA was originally isolated from two animal species, the dog and rat. The amino acid sequences from the two species are highly homologous, but completely different in the putative N-terminal, cytoplasmic region. Northern blot analysis using oligonucleotide probes unique to either of the two clones has revealed that the two forms of type V adenylylcyclase mRNA, canine form (= type V-a) and rat form (= type V-b), are co-expressed as splicing variants in both species. Genomic Southern blot analysis has suggested that the two forms are the products of a single gene. When overexpressed, however, deletion of the N-terminal domain did not alter any biochemical properties. Thus multiple splicing variants with unique N-terminal amino acid sequences of type V adenylylcyclase can be generated from a single gene, however, biochemical properties of these variants may not be different.

Adenylyl Cyclases↗

PubMed1995

[A case of peritoneal metastasis from retroperitoneal yolk sac tumor diagnosed by 67Ga-scan and 18F-FDG-PET].

Yolk sac tumor is one of the histological types of germ cell tumors. Primary retroperitoneal germ cell tumors are extremely rare neoplasms. We report a case of peritoneal metastasis after resection of a primary retroperitoneal germ cell tumor. The peritoneal metastases were detected by 67Ga-scan when CT did not suggest metastatic lesions while the level of alphafetoprotein was still elevated. The 67Ga-scan showed multiple hot spots in the abdomen and pelvis 72 hours after intravenous injection of the tracer and no changes were observed in serial scan taken 6 hours after the first scan. These findings were strongly suggested the dissemination of the malignant tumors. A PET study with 18F-fluorodeoxyglucose was performed and showed extensive uptake in the intraabdominal and intrapelvic cavity. It was also useful for understanding the extension and distribution of the peritoneal metastatic lesions. The sites of the accumulation of 18F-fluorodeoxyglucose corresponded to the results found in postmortem.

Adult↗

PubMed1995

[Assessment of bone mineralization of hemodialyzed patients with SPA and DPA--different effect of PTX with the site].

We analyzed the bone changes at each site of secondary hyperparathyroidism (2 degrees HPT) on hemodialyzed patients using both single photon absorptiometry (SPA) and dual photon absorptiometry (DPA). The subjects were 35 hemodialysis patients (12 male, 24 female) with 2 degrees HPT. The bone mineral densities (BMD) of 1/3 radius, head, total body and 3rd lumbar spine were measured before and after parathyroidectomy (PTX). Before PTX, the BMD of 2 degrees HPT patients were lower than the normal range of all sites, especially at the radius which mainly consisted of cortical bone. After PTX, the BMD at all sites increased especially in the head. The BMD of the radius also continued to increased up two years after PTX, but it was not as increased as the BMD of head. The BMD of the lumbar spine which consisted of cancellous bone mainly increased after PTX for one year and decreased thereafter. This decrease was influenced by age. There was a difference with the site of BMD after PTX. The determination of changes of BMD of head and radius was considered useful for the judgment of treatment.

Absorptiometry, Photon↗

PubMed1995

[Transrectal portal scintigraphy for evaluation of portal hemodynamics before and after TIPS].

In order to evaluate portal venous hemodynamics before and after TIPS, transrectal portal scintigraphy was performed in 8 patients. In all 8 patients, scintigram before TIPS demonstrated hepatofugal flow in the portal vein and less accumulation of radioisotope in the liver. In the scintigrams for follow-up of TIPS, the flow direction in the portal vein changed to be hepatopedal. In 3 of the patients in whom stent shunt was occluded after TIPS, the portal blood flow was turned to be hepatofugal again. It is concluded that transrectal portal scintigraphic studies of the TIPS patients provide noninvasive evaluation of portal hemodynamics.

Aged↗

PubMed1995

[Local cerebral blood flow and glucose metabolism during seizure in spontaneously epileptic El Mice].

Local cerebral blood flow and glucose metabolism were examined in spontaneously epileptic El mice using autoradiography with 125I-IMP and 14C-DG in the interictal phase and during seizure. El (+) mice that developed generalized tonic-clonic convulsions and El (-) mice that received no stimulation and had no history of epileptic seizures were examined. The seizure non-susceptible, maternal strain ddY mice were used as control. Uptake ratios for IMP and DG in mouse brain were calculated using the autoradiographic density. In the interictal phase, the pattern of local cerebral blood flow of El (+) mice was similar to that of ddY and El (-) mice, and glucose metabolism in the hippocampus was higher in El (+) mice than in El (-) and ddY mice, but flow and metabolism were nearly matched. During seizure, no significant changed blood flow and increased glucose metabolism in the hippocampus, the epileptic focus, and no markedly changed blood flow and depressed glucose metabolism in other brain regions were observed and considered to be flow-metabolism uncoupling. These observations have never been reported in clinical or experimental studies of epilepsy. Seizures did not cause large regional differences in cerebral blood flow. Therefore, only glucose metabolism is useful for detection of the focus of secondary generalized seizures in El mice, and appeared possibly to be related to the pathophysiology of secondary generalized epilepsy in El mice.

Animals↗

PubMed1994

A novel peptide inhibitor of adenylyl cyclase (AC). A peptide from type V AC directly inhibits AC catalytic activity.

Peptides derived from various regions of type V adenylyl cyclase (AC) were studied to determine their effect on AC catalytic activity. Out of 10 examined, only one peptide, peptide 2 (Lys425-Cys444), significantly inhibited both basal and stimulated (forskolin or GTP gamma S (guanosine 5'-O-thiotriphosphate)) type V AC catalytic activity overexpressed in CMT cells. The sequence of this peptide was taken from the first cytoplasmic domain of type V AC, which has a high sequence homology to other AC isoforms. Competition studies performed between the peptide and the substrate ATP showed that the inhibition was noncompetitive. Mutation or truncation of the peptide designed to destroy its secondary structure totally negated the inhibitory effect. This peptide also inhibited the catalytic activity of purified types II and V AC, as well as that of various cells, including S49 cyc- cells. Our data indicate that the peptide directly interacts with AC to inhibit catalytic activity; this provides new information regarding regions of the enzyme involved in its catalytic activation.

Adenylyl Cyclase Inhibitors↗

PubMed1994

Differential activation of adenylyl cyclase by protein kinase C isoenzymes.

Cyclic AMP production within cells is altered upon protein kinase C (PKC) activation; however, whether PKC directly modulates adenylyl cyclase (AC) catalytic activity has been controversial. Molecular studies have elucidated the existence of multiple PKC isoenzymes although the functional role of this diversity is not clear. Using purified PKC and AC isoenzymes, we demonstrate that PKC zeta directly phosphorylates type VAC, leading to an approximate 20-fold increase in its catalytic activity, a significantly larger enhancement than that achieved with forskolin (approximately 5-fold), the most potent activator of AC. When forskolin and PKC phosphorylation are combined, type V AC catalytic activity is increased 100-fold over basal levels. The two PKC isoenzymes (alpha and zeta) are additive in their capacity to activate AC, although PKC alpha is less potent than PKC zeta. Our data indicate that PKC can directly and potently regulate AC activity in an isoenzyme-specific manner, suggesting that direct cross-talk plays a major role in coordinating the activity of these two principal signal transduction pathways.

Adenylyl Cyclases↗

PubMed1994

[Usefulness of 99mTc-PMT SPECT and 18F-FDG PET in diagnosing orbital metastasis of hepatocellular carcinoma].

We reported a case in which 99mTc-PMT scintigraphy was useful in diagnosing orbital metastasis of HCC. The case involved a 70 y.o. male, who had undergone nine transcatheter arterial embolizations over two years because of HCC and who had a past history of gastric cancer. The patient had complained of headache and visual disturbance for two months. Cranial CT and MRI studies showed a large homogeneous mass with remarkable bone destruction in the right lateral orbital wall. Because AFP was elevated, orbital metastasis of HCC was suspected, and 99mTc-PMT scanning was performed. On the planar and SPECT images, very high uptake was found in the right orbital tumor. The FDG-PET study showed remarkable hypermetabolism in the medial portion of tumor and follow-up MRI revealed that the tumor had expanded and invaded to the medial side of the orbit. 99mTc-PMT scanning was critical in diagnosing this case of orbital metastasis, and FDG-PET imaging was useful in determining the most active portion of the tumor.

Aged↗

PubMed1994

[A case of mesenteric panniculitis: comparing the findings of 67Ga scintigraphy with pathological results].

We report a case of mesenteric panniculitis where we compared the findings of 67Ga-citrate (Ga) scintigraphy with pathological results. The patients, a 75-year-old man, was hospitalized for examination of low abdominal mass. After hospitalization he developed high CRP levels. A Ba enema revealed serrated intestinal walls and a thick fat density, the margins of which were distinct, as judged from abdominal CT scans. Therefore we suspected a mesenteric panniculitis. Since the patient did not improve under conservative treatment for three months, surgery was performed a day after Ga scintigraphy which showed the abnormal uptake in the abdominal mass, which was removed. The radioactivity of several tissue slices from the resected specimen containing the affected part which had been described inflammatory in the pathological examination showed very high radioactivity. This disease is usually diagnosed from the typical findings of Ba enema and CT scan. But, when an extraordinary abdominal accumulation presents, one should think of performing a Ga scan as an additional diagnostic parameter.

Aged↗

PubMed1994

[Evaluation of renal function by factor analysis using 99mTc-MAG3].

The kinetics of 99mTc-mercapto-acetyltriglycine (MAG3), a new renal scintigraphic agent, was studied by factor analysis in patients with chronic renal disorders, and its application to assessment of the renal function was evaluated. Data were collected for 30 minutes from immediately after intravenous injection of MAG3 at 370 MBq, the first pass image and serial renal scintigrams were obtained, and factor analysis was attempted simultaneously. Since most of MAG3 is excreted via the kidney during the first pass, factor analysis was performed. Two factors reflecting renal parenchymal components and pelvic components could be separated in 8 (Cre < or = 2.9 mg/dl) of 10 patients, and they corresponded with respective segmental renograms. In the remaining 2 (Cre > or = 3.0 mg/dl), separation was impossible by 2-factor analysis, and 3-factor analysis was needed. Factor analysis is considered to allow objective evaluation of renal function without setting the ROI.

Adult↗

PubMed1993

In vivo generation of an adenylylcyclase isoform with a half-molecule motif.

A truncated form of adenylylcyclase (type V-alpha) has been cloned from a cardiac cDNA library. It constitutes a half-molecule of type V adenylylcyclase diverging at the end of the first cytoplasmic loop. Northern blotting study has revealed the presence of such a mRNA species (approximately 3.5 kilobases in size) in the heart. Genomic sequence analysis has revealed that type V-alpha is generated via usage of a polyadenylation signal located within an intronic sequence of type V adenylylcyclase gene. When type V-alpha is co-expressed with an artificially generated half-molecule constituting the latter half of type V adenylylcyclase, the catalytic activity in transfected cell membranes is significantly higher than that of controls. However, when either alone is overexpressed, no significant increase in catalytic activity results. These results indicate that a half-molecule of adenylylcyclase, i.e. a protein containing six-transmembrane spans followed by a single cytoplasmic domain, can be generated in vivo, but catalytic activity is lacking unless heterodimerization can occur. This finding identifies another potential mechanism for generating diversity within this enzyme family.

Adenylyl Cyclases↗

PubMed1993

Role of endothelium in biphasic hypoxic response of the isolated pulmonary artery in the rat.

We investigated the roles of the endothelium in the hypoxic responses of the isolated main pulmonary artery (PA) in the rat. Hypoxia was induced by gassing an organ chamber with 95% N2 + 5% CO2 (PO2 = 34.6 +/- 3.1 Torr) instead of 16% O2 + 5% CO2 + balance N2 (PO2 = 92.8 +/- 3.0 Torr). Vascular rings were precontracted with 2 x 10(-8) M phenylephrine. A transient hypoxic contraction and a subsequent relaxation were observed in the endothelium-intact rings. The hypoxic contraction was reduced in the endothelium-denuded rings. In contrast, there were no significant differences between the hypoxic relaxation in the endothelium-intact and endothelium-denuded rings. Inhibitors of endothelium-derived relaxing factor (EDRF) activity, 2 x 10(-6) M NG-monomethyl-L-arginine (L-NMMA) and 10(-6) M methylene blue, produced 53% and 66% reductions in hypoxic contraction, respectively, Furthermore, the amount of cyclic GMP in the endothelium-intact PA rings which had been precontracted with phenylephrine decreased from 2.10 +/- 0.45 pmol/mg protein during normoxia to 0.90 +/- 0.18 pmol/mg protein during hypoxia. Indomethacin and OKY-046 did not influence hypoxic contraction or relaxation. These results suggest that hypoxic contraction of the isolated pulmonary artery in the rat is partially induced by inhibition of the release of EDRF.

Animals↗

PubMed1992

Down-regulation of protein kinase C potentiates atrial natriuretic peptide-stimulated cGMP accumulation in vascular smooth-muscle cells.

It has been reported that atrial natriuretic peptide (ANP) produces inositol phosphates and diacylglycerol in vascular smooth muscle cells (VSMC). The purpose of this study is to investigate whether diacylglycerol produced by ANP affects ANP-induced cyclic GMP (cGMP) accumulation through the activation of protein kinase C. Short-term (15 min) treatment of rat aortic VSMC with protein kinase C activating phorbol 12-myristate 13-acetate (PMA, 100 nM) decreased ANP (100 nM)-induced cGMP accumulation by 34.7% in the presence of IBMX (0.5 mM). However, the long-term (24 h) treatment to decrease the activity of protein kinase C led to an enhancement of the cGMP accumulation by 69.6% compared with that of control VSMC. There were no significant differences in Bmax and Kd for ANP and ANP-dependent particular guanylyl cyclase activity between long-term PMA-treated and control VSMC. In the present study, we show that the activation of protein kinase C attenuates the cGMP accumulation induced by ANP and that down-regulation of protein kinase C results in an enhancement of the cGMP accumulation. These data are consistent with the role of protein kinase C as a negative regulator in ANP-receptor/guanylyl cyclase pathway.

Animals↗