Biomedical subjects

J Ozawa

Publications and source records attributed to J Ozawa.

10 recordsLinked to original sources

PubMed1992

Possible involvement of both N- and L-type voltage-dependent Ca channels in adrenergic neurotransmission of canine saphenous veins in low Ca2+ plus tetraethylammonium medium.

The involvement of N- and L-type voltage-dependent Ca channels (VDCCs) in adrenergic neurotransmission under the superfusion with 0.25 mM Ca2+ + 20 mM tetraethylammonium (low Ca2+ + TEA) medium has been studied by examining the effects of omega-conotoxin GVIA (omega-CTX) and dihydropyridine antagonists and agonist on transmural nerve stimulation (TNS)-evoked 3H overflow from canine saphenous veins preloaded with [3H]-noradrenaline. Nisoldipine (10 and 30 microM) and nifedipine (30 microM) reduced significantly the TNS-evoked 3H overflow in low Ca2+ + TEA medium, while the two dihydropyridine antagonists failed to suppress it in normal Krebs medium. Bay K 8644 (30 and 100 nM) produced a significant and concentration-dependent enhancement of the TNS-evoked 3H overflow in low Ca2+ + TEA medium. The enhancing effects of Bay K 8644 were antagonized by both 3 microM nisoldipine and 10 microM nifedipine. omega-CTX inhibited markedly the TNS-evoked 3H overflow in both normal Krebs and low Ca2+ + TEA media, the inhibition by omega-CTX being ten times more potent in low Ca2+ + TEA medium. Nisoldipine (30 microM), when combined with 1 nM omega-CTX, produced a further significant inhibition of the TNS-evoked 3H overflow in low Ca2+ + TEA medium. However, no additional inhibition by 30 microM nisoldipine was observed when omega-CTX concentration was raised to 2 nM. In the veins superfused with normal Krebs medium, nisoldipine (30 microM) did not affect the inhibitory effect of 10 nM omega-CTX on the evoked 3H overflow.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic Fibers↗

PubMed1991

A selective effect of protein kinase C activators on noradrenaline release compared with subsequent contraction in canine isolated saphenous veins.

1. Effects of protein kinase C (PKC) activators and inhibitors on both tritium overflow and subsequent contraction evoked by transmural nerve stimulation (TNS) were investigated in canine saphenous veins prelabelled with [3H]-noradrenaline. 2. Activation of PKC by stepwise increasing concentrations (0.01 nM-1 microM) of 12-O-tetradecanoylphorbol 13-acetate (TPA), phorbol 12,13-dibutyrate (PDBu) or mezerein caused a significant and concentration-dependent enhancement of the tritium overflow evoked by TNS, while the activators failed to affect the corresponding contraction except with the highest concentration of PDBu when the contraction was significantly reduced. Phorbol, which is inactive on PKC, had no effects on the tritium overflow and contraction induced by TNS. 3. PKC inhibitors, polymyxin B (1 and 10 microM) and the isoquinolinesulphonamide, H-7 (1 microM), inhibited significantly the phorbol ester-potentiated tritium overflow evoked by TNS with no effects on the contraction. H-7 and the related inhibitor H-8 at 10 microM reduced significantly both responses to TNS in the presence of TPA, while they suppressed only the TNS-induced contraction in the absence of TPA. 4. None of the PKC activators or inhibitors affected the spontaneous tritium overflow. 5. PDBu (0.01 and 0.1 microM) elevated resting tension of the veins more effectively than TPA and mezerein. 6. These results suggest that PKC may modulate electrically stimulated noradrenaline release from adrenergic nerve endings of the canine saphenous veins and the PKC activators may act more selectively on presynaptic than postsynaptic sites, but have no apparent effect on postjunctional noradrenergic mechanisms.

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

PubMed1991

Presynaptic sites of isolated canine saphenous veins are more sensitive to protein kinase C than postsynaptic ones.

Effects of protein kinase C (PKC) activators and inhibitors on both tritium overflow and contraction evoked by 40 mM KCl were studied in canine saphenous veins preloaded with [3H]norepinephrine (NE). 12-O-Tetradecanoylphorbol 13-acetate (TPA) and phorbol 12,13-dibutyrate (PDBu) at 10(-11)-10(-7) M enhanced concentration-dependently the KCl-evoked tritium overflow, which was antagonized by polymyxin B (10(-5) M) and staurosporine (10(-7) or 10(-6) M). PDBu (10(-8) and 10(-7) M), but not TPA, potentiated the KCl-induced contraction. Only staurosporine reduced the KCl-induced contraction in the presence of PKC activators. Polymyxin B (3 X 10(-5) M) which failed to inhibit exogenous NE-induced contraction attenuated both responses to KCl. Staurosporine (10(-6) M) suppressed not only both the responses to KCl but also exogenous NE-induced contraction. Phentolamine (10(-6) M) inhibited almost completely the KCl-induced contraction and augmented remarkably the evoked tritium overflow. PDBu (10(-8) and 10(-7) M) still potentiated both responses to KCl in the phentolamine-treated veins. An additional treatment with nifedipine (10(-6) M) inhibited markedly the potentiation of the KCl-induced contraction by PDBu in the presence of phentolamine without affecting the evoked overflow. These results suggest that PKC may modulate KCl-evoked NE release from the adrenergic nerve endings of canine saphenous veins and that PKC is more sensitive to presynaptic than postsynaptic sites.

Animals↗

PubMed1991

Low Ca2+ plus tetraethylammonium medium: its usefulness in studying the effect of Ca antagonist on adrenergic neurotransmission.

The low Ca2+ + tetraethylammonium (TEA) medium enhanced electrically evoked norepinephrine release by 3.5-fold in canine saphenous veins. omega-Conotoxin GVIA (omega-CTX) inhibited the neurotransmission more markedly in low Ca2+ + TEA medium than in normal Krebs medium. This is the case for the inhibition by tetrodotoxin, though to a lesser extent. The inhibition by omega-CTX was competitively antagonized by elevating external Ca2+. The results indicate that low Ca2+ + TEA medium is useful for studying the effect of Ca antagonists on adrenergic neurotransmission, because omega-CTX acts more effectively in this medium.

Animals↗

PubMed1988

Interaction between chicken gizzard caldesmon and tropomyosin.

Chicken gizzard muscle caldesmon has been examined for ability to interact with tropomyosin from chicken gizzard muscle by using fluorescence enhancement of tropomyosin labeled with dansyl chloride (DNS) and affinity chromatography. The binding of caldesmon to tropomyosin was regulated by Ca2+ and calmodulin, i.e., at low ionic strength most of the caldesmon bound to tropomyosin-Sepharose 4B was co-eluted by adding calmodulin only in the presence of Ca2+, but not in its absence. This regulation by Ca2+ and calmodulin was also suggested by fluorescence measurements. Actin- and calmodulin-binding sites on the caldesmon molecule were located in the 38K fragment (Fujii, T., Imai, M., Rosenfeld, G.C., & Bryan, J. (1987) J. Biol. Chem. 262, 2757-2763). When 38K-enriched fraction was applied to the tropomyosin-Sepharose, the 38K fragment was retained by the column and could be eluted by adding Ca2+ and calmodulin.

Animals↗

PubMed1970