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Biomedical subjects

M Fukase

Publications and source records attributed to M Fukase.

At least 127 records · Page 7Linked to original sources
PubMed1988

Calcitonin gene-related peptide stimulates adenylate cyclase activation via a guanine nucleotide-dependent process in rat liver plasma membranes.

To evaluate the functional relationship between the liver calcitonin gene-related peptide (CGRP) receptor and guanine nucleotide-binding proteins, we investigated the effects of nucleotides not only on adenylate cyclase activation by CGRP, but also on 125I-[Tyr0]rat CGRP binding to rat liver plasma membranes. In the presence of GTP, rat CGRP stimulated adenylate cyclase activity in a dose-dependent manner in rat liver plasma membranes, and this effect was reduced in the absence of GTP. Salmon calcitonin also enhanced adenylate cyclase activation in the presence of GTP, but only in higher concentrations. On the other hand, guanine nucleotides not only decreased 125I-[Tyr0]rat CGRP binding to rat liver plasma membranes, but also accelerated the dissociation of label binding, and the removal of Mg2+ from incubation medium attenuated this inhibitory action of GTP on 125I-[Tyr0]rat CGRP binding to membranes. Scatchard analysis of the data revealed that the reduction of 125I-[Tyr0]rat CGRP binding by GTP was due to the decrease in binding affinity without a significant change in binding capacity. These findings lead us to conclude that binding of CGRP to its receptors activates adenylate cyclase in rat liver plasma membranes via a guanine nucleotide-dependent process, suggesting the involvement of guanine nucleotide-binding stimulatory protein in the action of CGRP.

Adenylyl Cyclases↗
PubMed1988

Parathyroid hormone degradation by chymotrypsin-like endopeptidase in the opossum kidney cell.

Cathepsin-D has been previously reported to cleave intact PTH into PTH-(1-34) and -(35-84) in membranous fractions of rat and bovine kidney. Whether PTH degradation occurs by intact kidney cells, however, has not been examined in detail. We have, therefore, examined this possibility using an opossum kidney (OK) cell line which possesses the characteristics of proximal renal tubules and responds to PTH. PTH radioimmunoreactivity recovered in trichloroacetic acid-soluble products and in fractions eluted from reverse phase HPLC was measured using an antibody directed to the midregion and C-terminus of PTH. In this study, intact OK cells, but not extracellular enzymes, cleaved human (h) PTH-(1-84) into three discrete fragments which were released into the medium in a time- and temperature-dependent fashion. Half-maximal velocity of PTH-degrading activity (PTHDA) was observed at 9 nM hPTH-(1-84). A 1000-fold molar excess of PTH antagonists [hPTH-(3-34) and [Tyr34]hPTH-(7-34)amide] markedly inhibited PTHDA, whereas ACTH, glucagon, or big gastrin did not suppress it, suggesting an involvement of the PTH receptor in PTHDA. This PTHDA was strongly inhibited by phenylmethylsulfonylfluoride and chymostatin, but not by trypsin inhibitor, elastatinal, or inhibitors of aspartic, cysteine, or metalloproteinases, suggesting that it is due to a seryl chymotrypsin-like endopeptidase. Analysis of chymotrypsin-digested products of hPTH-(1-84) eluted from HPLC exhibited five fragments detected by UV absorbance (210 nm), three of which were measurable by PTH RIA, and each corresponded to the three PTH fragments produced by OK cells. All three fragments were predominantly suppressed in the presence of chymostatin, suggesting that chymotrypsin-like activity is solely responsible for PTHDA in intact OK cells. To further explore the cleavage sites of PTH by chymotrypsin, amino acid analysis of chymotrypsin-cleaved products was performed. The results strongly support the conclusion that a chymotrypsin-like enzyme in OK cells cleaved the hormone between residues 23-24, and 34-35 to produce, at least, hPTH-(24-84) and -(35-84). Lysosomal blockers (chloroquine, ammonium chloride, or monensin) did not affect this PTHDA. Our present study indicates that chymotrypsin-like endopeptidase, but not other endopeptidase or lysosomal enzymes, is responsible for the limited hydrolysis of PTH by intact OK cells.

Amino Acids↗
PubMed1988

Hemangiopericytoma-induced osteomalacia: tumor transplantation in nude mice causes hypophosphatemia and tumor extracts inhibit renal 25-hydroxyvitamin D 1-hydroxylase activity.

Although more than 50 patients with the tumor-induced osteomalacia syndrome, characterized by remission of unexplained osteomalacia after resection of a coexisting tumor, have been reported, the pathogenesis of this syndrome is still not clear. We investigated the cause of biopsy-confirmed osteomalacia which was resistant to treatment with 1 alpha-hydroxyvitamin D3 in a 54-yr-old man. He had severe hypophosphatemia, a high serum alkaline phosphatase level, a low plasma 1,25-dihydroxyvitamin D level, and remarkably increased urinary phosphorus excretion. A tumor, with histological characteristics of a hemangiopericytoma, was found on his left thigh. After surgical removal of this tumor, his plasma 1,25-dihydroxyvitamin D and serum phosphorus levels increased to normal levels, and his bone pain subsided. The tumor was transplanted to athymic nude mice. A nodule formed in each mouse, with histological features identical to those of the original tumor, and the tumor-bearing mice had hypophosphatemia, high serum alkaline phosphatase levels, and increased urinary phosphorus excretion. When extracts of the original tumor were added to primary cultures of renal tubular cells, renal cAMP levels did not change, but 25-hydroxyvitamin D-1 alpha-hydroxylase activity was significantly inhibited. These data indicate tumoral production of some humoral factor(s) inhibiting 25-hydroxyvitamin D-1 alpha-hydroxylase activity and phosphorus reabsorption unrelated to adenylate cyclase-cAMP production in proximal renal tubules.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1988

Calcitonin-induced increase in phosphate accumulation in LLC-PK1 cells probably through protein kinase C activation.

To assess the role of protein kinase C and cAMP on the calcitonin-induced alteration of phosphate accumulation by renal tubular cells, the effects of phorbol esters, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), and DBcAMP on the phosphate accumulation in LLC-PK1 cells were investigated. Calcitonin stimulated phosphate accumulation with a concomitant increase in cAMP production. Phorbol esters and 1-oleoyl-2-acetyl-glycerol, activators of protein kinase C, also stimulated the phosphate accumulation. Furthermore, H-7, an inhibitor of protein kinase C, inhibited a calcitonin-induced increase in phosphate accumulation significantly. Although DBcAMP by itself did not increase the phosphate accumulation, it enhanced the stimulatory effect of 12-0-tetradecanoyl phorbol-13-acetate on the phosphate accumulation. Accordingly, protein kinase C as well as cAMP might be involved in the calcitonin-induced increase in phosphate accumulation in LLC-PK1 cells.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1988

Intestinal absorption of oyster shell electrolysate.

High voltage electric current was passed through oyster shell powder for electrolysis. The crystalline shape of oyster shell electrolysate appeared to be quite different from that of CaO or CaCO3. Higher serum calcium values were achieved by oral administration of the same amount of as oyster shell electrolysate than as calcium carbonate in vitamin D-deficient rats, suggesting a better intestinal absorption of the former than the latter. In four patients with postoperative hypoparathyroidism with reduced intestinal calcium absorption, the same amount of elementary calcium as oyster shell electrolysate was more effective than calcium carbonate in raising serum calcium in the absence of vitamin D supplement. Oyster shell electrolysate was also more effective in suppressing serum parathyroid hormone concentration than calcium carbonate in two patients with secondary hyperparathyroidism with renal failure. Calcium thus appears to be more readily absorbed from oyster shell electrolysate than from calcium carbonate through intestinal barriers produced by insufficient vitamin D action.

Adult↗
PubMed1987

Phorbol esters inhibit phosphate uptake in opossum kidney cells: a model of proximal renal tubular cells.

The effects of phorbol esters and diacylglycerol on phosphate uptake in opossum kidney (OK) cells were investigated to assess the possible role of Ca2+-activated, phospholipid dependent protein kinase (protein kinase C) on renal phosphate handling. OK cells are widely used as a model of proximal renal tubular cells and are reported to possess a Na+-dependent phosphate transport system. Phorbol-12,13-dibutyrate (PDBu) inhibited phosphate uptake. This inhibitory effect was synergistically enhanced with A23187. 4 beta-phorbol 12,13-didecanoate inhibited phosphate uptake, while 4 alpha-phorbol 12,13-didecanoate did not. 1-oleoyl-2-acetyl-glycerol (OAG), a synthetic diacylglycerol, also exhibited an inhibitory effect on phosphate uptake. These data suggest the possible involvement of protein kinase C in proximal renal tubular phosphate transport.

Animals↗
PubMed1987

Possible involvement of inositol phosphates and calmodulin in calcitonin-induced stimulation of phosphate transport in LLC-PK1 cells.

The present study investigated the possible involvement of phosphatidylinositol breakdown and Ca2+-calmodulin complex in the calcitonin-induced stimulation of phosphate transport in LLC-PK1 cells. This cell line with calcitonin receptors possesses Na+-dependent phosphate transport and has been employed as a model for studying the mechanism of renal tubular phosphate transport. (Asu1,7) eel calcitonin stimulated the phosphate transport in LLC-PK1 cells in a dose-dependent fashion with accompanying increase of inositol triphosphate (IP3) production. When the cells were preincubated with the potent calmodulin antagonist, w-7 or w-13, the stimulatory effect of calcitonin on phosphate transport was significantly inhibited. These findings indicate that Ca2+-calmodulin complex formed by increased cytosolic Ca2+, which is mobilized from intracellular pools by IP3, may be involved in the signal transduction of calcitonin in these cells.

Animals↗
PubMed1987

Defective adaptation to a low phosphate environment by cultured renal tubular cells from X-linked hypophosphatemic (Hyp) mice.

Effects of parathyroid hormone (PTH), low phosphate environment, and 12-O-tetradecanoyl phorbol-13-acetate (TPA) on the phosphate reabsorption by the renal tubular cells from mutant hemizygous hypophosphatemic (Hyp/Y) mice and their littermates (+/Y) were studied using a phosphate accumulation system which had been developed recently. This system mimics phosphate transport at the renal tubules. When cultured in a normal phosphate medium, the characteristics of the phosphate accumulation by Hyp cells was almost identical with that by normal cells; a PTH-induced inhibition and a TPA-induced stimulation of phosphate accumulation. However, when preincubated in a low phosphate medium, the accumulation of phosphate by normal cells increased significantly, while that by Hyp cells did not. These results indicate that the adaptation to the low phosphate environment is defective in Hyp cells and it may be one of the cause of renal phosphate leakage in the Hyp mouse.

Alkaline Phosphatase↗
PubMed1987

Arachidonic acid inhibits phosphate transport by cultured renal cells.

Because arachidonic acid and its metabolites are reported to be intracellular messengers of various exogenous stimuli, we studied whether arachidonic acid influences phosphate transport by cultured mouse renal epithelial cells. Arachidonic acid, at 10(-7)-10(-4)M, inhibited phosphate transport without influencing cyclic adenosine 3':5'-monophosphate production. Nordihydroguaiaretic acid and indomethacin, inhibitors of arachidonic acid metabolism, did not cancel the arachidonic acid-induced inhibition of phosphate transport. Furthermore, unsaturated fatty acids other than arachidonic acid also inhibited phosphate transport and their inhibitory effect increased as the number of double bond increased. These data demonstrate that arachidonic acid inhibits the phosphate transport by the cultured renal epithelial cells, probably not via conversion to its metabolites.

Animals↗
PubMed1987

Possible involvement of protein kinase C in parathyroid hormone degradation by osteoblast-like rat osteosarcoma cell line UMR106.

The effects of 12-O-tetraadecanoyl phorbol-13-acetate (TPA), 1-oleoyl-2-acetyl-glycerol (OAG), and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) on the parathyroid hormone (PTH) degrading activity in a PTH-responsive osteoblast-like rat osteosarcoma cell line UMR106 were investigated to assess the role of Ca2+-activated. Phospholipid dependent protein kinase (protein kinase C) on the degradation of hormones. TPA and OAG, activators of protein kinase C, enhanced the PTH degrading activity dose-dependently, whereas H-7, an inhibitor of protein kinase C, exhibited a dose-dependent inhibition on this activity. These data suggest that protein kinase C activation may enhance PTH degrading activity by UMR106 cells as a possible regulator of PTH degradation.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1987

Synthetic parathyroid hormone fragments shortened at the amino terminus stimulate glucose-6-phosphate dehydrogenase activity in the distal renal tubule.

The cytochemical bioassay, using glucose-6-phosphate dehydrogenase (G6PD) activity in the distal convoluted tubule of a guniea pig as an index, is specific and the most sensitive method of evaluating the biological activity of parathyroid hormone (PTH). Using this method, biological activities of the amino- or carboxyl-terminal PTH fragments and analogues, human (h) PTH-(3-34), [Tyr34]hPTH-(7-34)amide(NH2), [Tyr34]hPTH-(13-34)NH2, hPTH-(39-84), hPTH-(51-84), hPTH-(69-84), were tested over a concentration range of 10(-16) to 10(-13) M. In addition, the combined effect of these hormones with human or bovine PTH-(1-84) and the effect of dibutyryl (Bu)2) cAMP were also evaluated. In the 14-min time-course study, amino-terminal PTH fragments and analogues induced cyclic changes of G6PD activity with shorter cycle lengths in higher concentrations and with constant peak heights regardless of the concentrations. Human and bovine PTH-(1-84) showed the same activity on G6PD activation at 6 min. hPTH-(3-34), [Tyr34]hPTH-(7-34)NH2, and [Tyr34]hPTH-(13-34)NH2 were equipotent with PTH-(1-84) on a molar basis, and none of these analogues inhibited PTH-(1-84) even with doses up to 240 times that of PTH-(1-84). Carboxyl-terminal PTH showed no effect. (Bu)2cAMP mimicked the effect of PTH-(1-84) on G6PD activation in time course and dose response. We conclude that the amino terminus is not essential for the biological activity of PTH in the cytochemical bioassay.

Animals↗
PubMed1987

Phosphate transport by reconstructed monolayers from cultured mouse kidney cells.

A reconstructed monolayer was formed using epithelial cells from normal mouse kidney to investigate the hormonal effect on phosphate transport by the renal cells. The cells, when cultured on a Millipore filter, formed a monolayer with an apical negative transepithelial potential of 8.4 +/- 0.4 mV. When radioactive phosphate was added onto the apical surface of the monolayer (corresponding to the luminal surface of a renal tubule), the phosphate was transported through the cell layer to the basolateral surface (corresponding to the peritubular surface of a renal tubule). This transport process was saturable, energy-dependent, and inhibited by 2,4-dinitrophenol or ouabain. Dose-dependent parathyroid hormone-induced inhibition (73% of the control) was also evident in this system. Similar inhibition (69% of the control) was observed with DBcAMP. Thus, monolayers reconstructed from cultured mouse kidney cells show characteristics similar to those of renal tubules.

2,4-Dinitrophenol↗
PubMed1987

Calcium-dependent activation of glucose-6-phosphate dehydrogenase by 1,25-dihydroxycholecalciferol in the guinea pig distal convoluted tubule.

The effect of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) on glucose-6-phosphate dehydrogenase (G6PD) activity in the distal convoluted tubule of a vitamin D-depleted guinea pig was determined using quantitative cytochemistry. When kidney segments were incubated with 1,25(OH)2D3 (0, 0.15, 0.30, 1.5 or 3.0 nM) during the initial 5 h maintenance culture, G6PD activity at each steroid concentration decreased gradually to reach its stable basal level, which was higher in proportion to the increasing concentration of 1,25(OH)2D3. 1,25(OH)2D3-induced activity of this enzyme was completely abolished by cycloheximide (35 microM). In the presence of 1.5 nM 1,25(OH)2D3, at 0.15 mM calcium, increasing concentrations of EGTA from 0.1 to 2.0 mM caused a dose-dependent reduction in the enzyme activity and abolished it to the cycloheximide-treated level at 2 mM, whereas in the absence of 1,25(OH)2D3, the enzyme activity remained unchanged regardless of the concentration of calcium. These results indicate that G6PD is activated by 1,25(OH)2D3 via new protein synthesis, and that the extracellular calcium plays a crucial role in the regulation of this enzyme activity.

Animals↗