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Biomedical subjects

K Yamagami

Publications and source records attributed to K Yamagami.

At least 91 records · Page 5Linked to original sources
PubMed1988

Fluoroaluminates stimulate histamine secretion in the digitonin-permeabilized rat mast cells.

The combination of NaF and AlCl3 stimulated histamine secretion from digitonin-permeabilized rat mast cells only in the presence of trace amount of Ca2+. When NaF plus AlCl3 were added together with a maximal dose of guanosine-5'-[gamma-thio]triphosphate (GTP gamma S), the combined effect was less than additive. The results suggest that the secretory effect of fluoroaluminates is, at least partially, mediated by GTP-binding protein, which is previously found to be activated by GTP gamma S.

Aluminum↗
PubMed1987

The secretory mechanism in adrenal chromaffin cells by nitrophenol compounds: possible involvement of the change in the surface potentials.

The rabbit adrenal gland was perfused with a modified Locke's medium and the mechanism of adrenaline secretion induced by nitrophenol compound was investigated. The secretory response to 2,4-dinitrophenol (DNP) or trinitrophenol (TNP) showed the following peculiar features. (1) Prolonged exposure to DNP or TNP caused an immediate, and long-lasting increase of secretion only in the presence of Ca. (2) The response to DNP depended on the concentration of Ca, but that to TNP was largest in the presence of 0.5 mM Ca. (3) Re-addition of 2 mM Ca during prolonged exposure to DNP or TNP produced a larger response than did the simultaneous addition of Ca and either DNP or TNP. (4) The response to DNP in the presence of 2 mM Ca was markedly reduced by removal of external Na, but the Na dependency became less marked in the presence of 0.1 mM Ca. The response to TNP in the presence of 0.5 mM Ca was slightly reduced in the absence of Na. (5) DNP or TNP caused a much larger response during depolarization with a high K, Rb, or Cs medium than that with a 5 mM KCl medium. (6) The response to DNP was largely potentiated in the absence of most ions in the presence of only 0.1 mM Ca and that to TNP was potentiated in the presence of only 0.5 mM Ca under the same condition. (7) Re-addition of Ca 5 min after the removal DNP or TNP still caused substantial secretion. These results suggest that nitrophenol compounds stimulate secretion by two independent mechanisms: one is related to its effect on the surface potentials of the plasma membrane and the other unknown except for the possible dependence of Na and Ca.

2,4-Dinitrophenol↗
PubMed1983

Specific cleavage of calmodulin-binding proteins by low Ca2+-requiring form of Ca2+-activated neutral protease in human platelets.

Occurrence of Ca2+-dependent calmodulin-binding proteins in lysed human platelets and their cleavage by low Ca2+-requiring Ca2+-activated protease were investigated by a gel overlay technique using [125I]calmodulin. Calmodulin-binding polypeptides of Mr 100K, 90K, 60K, and 40K were detected in lysed platelets, of which 90K and 60K polypeptides were rapidly degraded to lower molecular weight products in the presence of micromolar concentrations of Ca2+. Then, we investigated cleavage of calmodulin-binding proteins by purified low Ca2+-requiring Ca2+-activated neutral protease from human platelets. As substrate, myosin light chain kinase and caldesmon purified from the chicken gizzard smooth muscle were used. In the presence of micromolar concentration of Ca2+, these two proteins were also rapidly degraded to lower molecular weight species, which were still capable of binding to calmodulin.

Animals↗
PubMed1982

Nitriphenol compound induces Ca-dependent exocytotic secretion of catecholamines by a direct effect on the plasma membranes of the adrenal medullary cells.

2,4-Dinitrophenol induced Ca-dependent secretion of adrenaline from the perfused adrenals of the rabbits. Secretion of adrenaline was accompanied by that of dopamine-beta-hydroxylase showing the exocytotic nature, 2,4,5-Trinitrophenol, which is devoid of uncoupling activity, and other nitrophenol compounds were also effective in inducing secretion, suggesting that secretion by nitrophenol compound is due to increased Ca entry through its direct effect on the plasma membrane.

2,4-Dinitrophenol↗
PubMed1981

Dynamics of calmodulin and cyclic AMP phosphodiesterase in plasma membranes of rat livers and ascites hepatomas.

1. Plasma membranes from ascites hepatoma cells (AH-7974, AH-130) contained much smaller amounts of calmodulin (about half) and cyclic AMP phosphodiesterase (about one-third) compared to plasma membranes of rat livers. 2. Some of calmodulin molecules in liver plasma membranes were released by repeated washing. The 'washed' liver plasma membranes showed the presence of specific binding sites for externally added calmodulin molecules (bovine brain) (N = 140 pmol/mg protein, Kd = 7.9 . 10(-8) M). The calmodulin content of AH-7974 plasma membranes was not reduced by repeated washing. The binding of calmodulin to the 'washed' AH-7974 plasma membranes was only of nonspecific nature with negative cooperativity. 3. Plasma membranes (liver and AH-7974) appeared to contain both calmodulin-dependent and calmodulin-independent phosphodiesterase, but the stimulation by externally added Ca2+ plus calmodulin was rather small. Externally added calmodulin-dependent phosphodiesterase (bovine brain) was bound more to 'washed' liver plasma membranes than to 'washed' AH-7974 plasma membranes. Newly bound phosphodiesterase appeared to be more sensitive to the stimulation by Ca2+ plus calmodulin in 'washed' hepatoma plasma membranes than in 'washed' liver plasma membranes. 4. Preincubation of 'washed' plasma membranes (liver and hepatoma) with calmodulin did not affect the binding of phosphodiesterase, but the sensitivity of phosphodiesterase to the stimulation by Ca2+ plus calmodulin in hepatoma plasma membranes was lost.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1981

Possible occurrence of Na+-dependent Ca2+ influx mechanism in isolated bovine chromaffin cells.

Chromaffin cells were isolated from bovine adrenals and the effects of experimental manipulations which alter the level of internal Na+ on the release of catecholamines and 45Ca uptake by these cells were investigated. In response to NA+ deprivation both parameters were increased or decreased when internal NA+ was raised or reduced, respectively. The results suggest the existence of Na+-dependent Ca2+ influx mechanism in these cells.

Animals↗
PubMed1981

Exocytotic secretion of catecholamines from the cat adrenal medulla by sodium deprivation: involvement of calcium influx mechanism.

1 Cat adrenal glands were perfused with Ca-deficient medium and secretion of catecholamines (CA) was induced by perfusion with Na-free medium in which NaCl was replaced by an osmotically equivalent amount of sucrose. 2 Release of CA and dopamine-beta-hydroxylase (DBH), but not that of phenylethanolamine-N-methyltransferase, was concomitantly found in the effluents when the adrenals were stimulated, indicating that secretion was due to exocytosis. 3 Secretion of CA induced by Na-free (sucrose) medium was dependent on the concentration of Ca and was saturated at 0.5 mM of Ca. 4 Sr or Ba substituted for Ca in maintaining secretion by Na-free (sucrose) medium. 5 The addition of Na, Li or alkali metal ions to Na-free (sucrose) medium containing Ca reduced the response to a variable extent but this inhibition was reversed by raising the concentration of Ca in the Na-free medium. 6 All of the Na substitutes used induced secretion only when this medium contained Ca. However, different Na substitutes released different amounts of CA; sucrose was most effective, K, Tris and choline were moderately and Li least effective. 7 Secretion of CA by Na-free (sucrose) medium was strongly inhibited by D-600, tetracaine or divalent cations such as Co, Ni, Zn and Mg. The inhibition by Co was partially reversed by raising the concentration of Ca in the Na-free medium. 8 Secretion of CA from bovine isolated chromaffin cells was induced by Na-deficient (sucrose) medium and was dependent on the concentrations of ionized Ca involved. 9 All the Na substitutes tested increased secretion of CA and 45Ca uptake, in a parallel fashion. 10 A correlation between secretion and 45Ca uptake was found under various experimental manipulations which reduced secretion of CA. 11 These results demonstrated that unlike the perfused bovine adrenals, the Ca influx mechanism is essential for secretion by Na deprivation in the perfused cat adrenals as it is in bovine isolated chromaffin cells. 12 It is suggested that Na deprivation increases Ca entry through the Ca channels by eliminating the competition between Na and Ca, and possibly by activating Ca influx linked with Na efflux.

Adrenal Medulla↗
PubMed1980

Studies on the angioarchitecture of the posterior choroid in rat and role of posterior ciliary vein.

Vascular casts were made by injection of low-viscosity plastic in eight Wistar-Kyoto rats, and the posterior half of the ocular wall was observed using the semiultrathin section method. Veins which connect with the capillaries of the posterior choroid include a venous system independent of the cortex vein and running parallel to the long and short posterior ciliary arteries. The veins flow into a venous ring which is located in the region at which the arterial circle of Zinn is said to be. There was no structure in this region which could be described as an arterial circle. From the above findings, it is concluded that these venous systems are part of the posterior ciliary vein and that they play an important role as a pathway for irrigation of blood from the posterior choroid.

Anatomy↗
PubMed1979

Ca2+ binding sites in plasma membranes of rat liver and hepatoma cells, and effect of concanavalin A on the Ca2+ binding sites and cellular uptake of Ca2+.

1. Plasma membranes isolated from rat livers and ascites hepatoma cells (AH-130, AH-7974) were assayed for specific Ca2+ binding sites using 45Ca2+ and a Millipore filtration technique. The presence of higher (Kd = 1.4--1.5 . 10(-5) M) and lower (Kd = 0.9--1.0 . 10(-4) M) affinity sites in both liver and hepatoma membranes was observed. The hepatoma plasma membranes however, showed 1.4--2.1-fold as many Ca2+ binding sites (higher and lower affinity sites) as the liver plasma membranes on the basis of protein. 2. Concanavalin A stimulated the specific Ca2+ binding to liver and hepatoma plasma membranes, showing a maximal stimulation (3--5-fold) at 100 microgram/ml. Succinyl concanavalin A was less effective, whereas wheat germ agglutinin and ricinus lectin were ineffective. 3. Concanavalin A stimulated the Ca2+ uptake by AH-7974 cells. The concanavalin A-mediated stimulation of Ca2+ uptake showed lectin-concentrations and Ca2+-concentration dependencies similar to those in the concanavalin A-mediated stimulation of Ca2+ binding.

Animals↗