ATPase In Synaptic Vesicles Research Articles

Estimation of the mitochondrial calcium pool in rat brain synaptosomes using Rhod-2 AM fluorescent dye

The literature data on the role of synaptic mitochondria in the regulation of the cytosolic calcium level are contradictory. In the present paper calcium storage by mitochondria in rat brain synaptosomes using the fluorescent dye Rhod-2 has been investigated. The addition of 60 mM KCl increases Rhod-2 fluorescence. This effect is completely abolished by replacing K+ with Na+ or withdrawing Ca2+ from the incubation medium. A proton ionophore, carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone, and a mixture of rotenone/oligomycin mitochondrial toxins cause a two-fold decrease in Rhod-2 fluorescence. Thapsigargin, an inhibitor of endoplasmic reticulum ATPase (1 μM), but not bafilomycin, an inhibitor of ATPase in synaptic vesicles (500 nM) also leads to a mitochondrial calcium influx. The addition of calcium to synaptosomes with the retained plasma membrane potential increased Rhod-2 fluorescence; however, this effect is insensitive to carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone. We have shown that mitochondria can serve as a calcium store in synaptosomes only in the case of a high cytosolic concentration of calcium.

The ATPase of cholinergic synaptic vesicles is associated with sugars

The ATPase in synaptic vesicles isolated from Torpedo californica electric organ can be nearly completely solubilized in octaethyleneglycoldodecyl ether containing buffer where it is stable only in a narrow pH range around neutrality. Solubilized ATPase adsorbs to Sepharose columns containing covalently linked Triticum vulgaris, Concanavalin A, Glycine max, Dolichos biflorus, Lens culinaris or Pisum sativum lectins in a manner responding to cognate sugar block or enzymatic deglycosylation in most cases. However, reproducible elution of adsorbed ATPase activity with cognate sugars could not be obtained. It is concluded that the cholinergic synaptic vesicle ATPase is a glycoprotein or it interacts with glycolipid.

The role or non-role of ATPase activation by phenytoin in the stabilization of excitable membranes.

The role or non-role of NaK ATPase, Mg ATPase, and CaMg ATPase involvement in stabilization of excitable membranes by phenytoin is critically evaluated. There is no substantial evidence to indicate that the membrane-stabilizing effect of phenytoin is due to activation of the NaK ATPase. Previous reports of activation of the NaK ATPase at low potassium and high sodium are probably not due to phenytoin but to a potassium contamination in the phenytoin solution. In vitro experiments do not provide any clear evidence of any alterations of NaK ATPase properties by phenytoin. However, one cannot rule out the possibility that phenytoin alters the efficiency of the sodium-potassium pump. Likewise, the Ca ATPase is not inhibited by phenytoin. However, there is some evidence that the Mg ATPase in synaptic vesicles is substantially inhibited by phenytoin. There is substantial evidence indicating that phenytoin partially blocks passive diffusion of sodium into stimulated nerves. The mechanism by which phenytoin blocks sodium influx and the relationship of this effect to the drug's anticonvulsant action remain to be determined.