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S Ichida

Publications and source records attributed to S Ichida.

69 records · Page 4Linked to original sources
PubMed1980

Inhibitory effect of dibutyryl cyclic GMP on potassium-stimulated 45Ca uptake by synaptosomes from rat brain.

The effects of dibutyrl cyclic GMP (db-cGMP) and dibutyryl cyclic AMP (db-cAMP) on potassium-stimulated 45Ca uptake by the P2 fraction of Gray and Whittaker were investigated with the following results. (1) db-cGMP inhibited the initial rate of potassium-stimulated 45Ca-uptake in a dose-dependent manner in 0.1 mM Ca0 medium, but had no effect on the uptake in low K+ medium. In 0.1 mM Ca0 medium, the concentration of db-cGMP causing 50% inhibition was about 3 mM. db-cAMP (5 mM) had no effect on the uptake. (2) db-cGMP-inhibited potassium-stimulated 45Ca uptake in 1 mM Ca0 medium, though less than in 0.1 mM Ca0 medium. (3) db-cGMP inhibited potassium-stimulated 45Ca uptake by synaptosomes (pinched-off nerve terminals) more than the uptakes by other subfractions of P2 fraction. It is suggested from the results that cGMP inhibits the Ca influx resulting from depolarization of the nerve endings in situ.

Animals↗
PubMed1980

Subsynaptosomal distribution of 45Ca taken up by synaptosomes in high-potassium medium.

The 45Ca uptake of synaptosomes was stimulated by high K+, and the K-stimulated uptake was temperature dependent and reached a plateau level within 20 sec at 30 degrees C. The synaptosomes which took up 45Ca in high-K+ medium for 20 sec was disrupted, and subsynaptosomal distribution of 45Ca was examined. The percentage increases of 45Ca labeling of fractions D (vesicles), C (myelin), B (synaptic plasma membrane), and A (mitochondria) induced by high potassium were 27.7 +/- 10.3%, 28.7 +/- 10.4%, 31.0 +/- 4.0%, and 48.1 +/- 5.5%, respectively. However, total counts of K-stimulated 45Ca labeling in fraction B was equal to that in fraction A, and those in fractions C and D were less. These observations indicate that Ca binding on the synaptic plasma membrane may be as important as a Ca reservoir or regular of Ca2+ in nerve terminals as the mitochondria.

Absorption↗
PubMed1980

Effect of verapamil on 45Ca uptake by synaptosomes.

The effect of verapamil on K-stimulated 45Ca uptake (the difference between uptake in 60 mM-Ko medium and 5 mM-Ko medium) was studied using a synaptosomal fraction from rat brain. Verapamil inhibited K-stimulated 45Ca uptake, but not 45Ca uptake in 5 mM-Ko media (1 mM- and 0.1 mM-Cao media). The concentrations of verapamil inducing 50% inhibition of K-stimulated 45Ca uptake (ID50) in 1 mM- and 0.1 mM-Cao media were not significantly different, being about 10(-4) M and 2 X 10(-4) M, respectively. Like verapamil, Mn++ inhibited only K-stimulated 45Ca uptake, but its ID50 values in 1 mM- and 0.1 mM-Cao media were about 1.7 mM and 0.2 mM, respectively. It is considered from these findings that both verapamil and Mn++ specifically inhibit K-stimulated 45Ca uptake, but the modalities of their inhibitory effects on K-stimulated 45Ca uptake are different.

Animals↗
PubMed1978

Effects of synaptic plasma membranes on release of acetylcholine from synaptic vesicles.

The influences of synaptic plasma membranes on release of acetylcholine (ACh) from synaptic vesicles isolated from rat brain were examined. In the presence of ATP, Mg++ and Ca++ but absence of cytoplasm from the nerve endings, the synaptic plasma membranes did not increase ACh release indicating absence of a stimulating factor which is known to be present in the cytoplasm. In presence of ATP, Mg++, Ca++ and the cytoplasm, the synaptic plasma membranes inhibited ACh release from the synaptic vesicles in high K+ medium, though not in high Na+ medium. Binding of Ca++ by the synaptic plasma membranes was dependent on ATP, inhibited by Na+ and stimulated by K+. Thus, the synaptic plasma membranes may inhibit ACh release in high K+ medium due to reduction in the concentration of free Ca++.

Acetylcholine↗
PubMed1978

Muscarinic cholinergic receptors in mammalian brain: differences between bindings of acetylcholine and atropine.

Studies were made on the bindings of [3H]-acetylcholine and [3H]-atropine to synaptic plasma membranes from rat brain. Synaptic plasma membranes have reversible, high affinity binding sites for both ligands, the KD values for ACh and atropine being about 20 nM and 1 nM, respectively. The maximal binding capacities for ACh and atropine, respectively, are 0.8-1.2 pmoles and about 1.5 pmoles/mg protein of synaptic membranes. The specific binding of ACh is almost completely inhibited by oxotremorine and atropine. 5,5'-Dithiobis (2-nitrobenzoic acid) (DTNB) increased the ACh-binding to about 1.5 pmole/mg protein. It also increased the inhibition of atropine-binding by ACh about 10-fold. Marked discrepancies were found in the inhibitions of atropine- and ACh-bindings by muscarinic agonists, but not in the inhibitions by antagonists. These findings support the hypothesis that muscarinic receptors have different sites for agonists and antagonists. The possibility that one receptor can be simultaneously occupied by both an agonist and an antagonist is also discussed.

Acetylcholine↗
PubMed1976

Effects of Na+ and other monovalent cations on Ca-efflux from synaptosomes.

Effects of monovalent cations on Ca-efflux were examined in rat brain cortex slices, synaptosomes and synaptic plasma membranes. Effluxes of 45Ca from brain slices and synaptosomes were stimulated by Na+ in medium and the effects of Na+ on the 45Ca-effluxes disappeared at low temperature. Furthermore, we observed that Rb+ had more effect than Na+ on 45Ca-efflux from the synaptosomes, while Li+ had less effect. On the other hand, release of 45Ca from the synaptic plasma membranes which had been preincubated with ATP, MG++ and 45Ca was stimulated by Na+ and Li+. But Cs+ and Rb+ were less effective on the release. These results indicate occurrence of Na-dependent Ca-efflux at nerve endings. However, the assumption that ATP-dependent Ca-binding with synaptic plasma membranes may be a partial reaction of Ca-efflux was not supported by these experiments.

Animals↗
PubMed1976

Effects of La+++, Mn++ and ruthenium red on Mg-Ca-ATPase activity and ATP-dependent Ca-binding of the synaptic plasma membrane.

The effects of La+++, Mn++ and ruthenium red (R.R.) on Ca-uptake of synaptic plasma membranes (S.P.M.) were investigated. La+++ (0.1 mM), Mn++ (0.2 mM) and R.R. (0.1 mM) selectively inhibited Mg-Ca-ATPase but did not significantly affect Mg-ATPase activity. The apparent Ki values of La+++, Mn++ and R.R. for Mg-Ca-ATPase were 0.05, 0.06 and 0.03 mM, respectively. La+++, Mn++ and R.R. did not affect Ca-uptake at concentrations which strongly inhibited Mg-Ca-ATPase activity. These results indicate that Ca-uptake by S.P.M. differ from that by sarcoplasmic reticulum.

Adenosine Triphosphatases↗
PubMed1976

Bound forms of Ca taken up by the synaptic plasma membrane.

Temperature dependent Ca-binding by the synaptic plasma membrane was increased in the presence of ATP and Mg++. Apparent Km for ATP was about 2.8 X 10(-5) M and optimal concentration of Mg++ was 2 mM in the presence of 2 mM ATP. After preincubation with nonradioactive Ca++, ATP and Mg++ to attain a steady state, addition of 45Ca resulted in remarkable labelling of the membrane, indicating rapid turnover of most of the membrane bound Ca. The presence of oxalate (60 mM) greatly increased Ca up-take on prolonged incubation. The Ca uptake in presence and absence of oxalate had similar substrate specificity and was similarly influenced by various monovalent cations. Furthermore, activities for Ca-uptake in the presence and absence of oxalate could not be separated by sucrose density gradient centrifugation of the synaptic plasma membrane fraction. Accordingly, it was considered that Ca++ in the medium was taken up by surface of the membrane, ATP- and temperature-dependently and then transferred into a cavity where the Ca-oxalate complex is formed.

Adenosine Triphosphate↗