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Ca2+ Sensitivity of Synaptic Vesicle Dopamine, ?-Aminobutyric Acid, and Glutama...
Gonçalves, Paula P.; Meireles, Sandra M.; Neves, Paulo; Vale, M. Graça P.The effect of Ca2+ on the uptake of neurotransmitters by synaptic vesicles was investigated in a synaptic vesicle enriched fraction isolated from sheep brain cortex. We observed that dopamine uptake, which is driven at expenses of the proton concentration gradient generated across the membrane by the H+-ATPase activity, is strongly inhibited (70%) by 500 µM Ca2+. Conversely, glutamate uptake, which essentially ...
Distinction between Ca2+ pump and Ca2+/H+ antiport activities in synaptic vesic...
Gonçalves, Paula P.; Meireles, Sandra M.; Neves, Paulo; Vale, M. Graça P.Synaptic vesicles, isolated from a sheep brain cortex, accumulate Ca2+ in a manner that depends on the pH and pCa values. In the presence of 100 [mu]M CaCl2, most of the Ca2+ taken up by the vesicles was vanadate-inhibited (86%) at pH 7.4, whereas at pH 8.5, part of the Ca2+ accumulated (36%) was [Delta]pH-dependent (bafilomycin and CCCP inhibited) and part was insensitive to those drugs (31%). We also observed...
Methods for analysis of Ca2+/H+ antiport activity in synaptic vesicles isolated...
Gonçalves, Paula P.; Meireles, Sandra M.; Neves, Paulo; Vale, M. Graça P.The involvement of Ca2+-storage organelles in the modulation of synaptic transmission is well-established [M.K. Bennett, Ca2+ and the regulation of neurotransmitter secretion, Curr. Opin. Neurobiol. 7 (1997) 316-322 [1]; M.J. Berridge, Neuronal calcium signaling, Neuron 21 (1998) 13-26 [2]; Ph. Fossier, L. Tauc, G. Baux, Calcium transients and neurotransmitter release at an identified synapse, Trends Neurosci. ...
Synaptic vesicle Ca2+/H+ antiport: dependence on the proton electrochemical gra...
Gonçalves, Paula P.; Meireles, Sandra M.; Neves, Paulo; Vale, M. Graça P.Synaptic vesicles isolated from sheep brain cortex accumulate Ca2+ by a mechanism of secondary active transport associated to the H+-pump activity. The process can be visualized either by measuring Ca2+-induced H+ release or [Delta]pH-dependent Ca2+ accumulation. We observed that the amount of Ca2+ taken up by the vesicles increases with the magnitude of the [Delta]pH across the membrane, particularly at Ca2+ c...
Ionic selectivity of the Ca2+/H+ antiport in synaptic vesicles of sheep brain c...
Gonçalves, Paula P.; Meireles, Sandra M.; Neves, Paulo; Vale, M. Graça P.As we previously reported, synaptic vesicles isolated from sheep brain cortex contain a Ca2+/H+ antiport that permits Ca2+ accumulation inside the vesicles (~5 nmol/mg protein) at expenses of the pH gradient generated by the H+-pumping ATPase. We observed that the system associates Ca2+ influx to H+ release and operates with low affinity for Ca2+. In the present work, we found that Ca2+/H+ antiport mediates exc...
Differentiation between Several Types of Phosphohydrolases in Light Microsomes ...
Vicente, Joaquim A. F.; Vale, M. Graça P.The phosphohydrolase activity of a light microsomal fraction isolated from corn roots (Zea mays L. cv LG 55) was investigated. The fraction, which appears to be enriched in endoplasmic reticulum and Golgi membranes, has ATPase and pyrophosphatase activities that hydrolyze ATP and pyrophosphate at an optimum pH of 7.0, with Km values of about 160 and 240 micromolar and with Vmax values of about 200 and 50 nanomo...
Ca2(+)-dependent binding of tamoxifen to calmodulin isolated from bovine brain
Lopes, M. Celeste F.; Vale, M. Graça P.; Carvalho, Arsélio P.The interaction of the antiestrogen tamoxifen (Tx) with calmodulin (CaM) was investigated by cross-linking between the protein and [3H] tamoxifen aziridine. We observed that CaM binds Tx in a Ca2(+)-dependent manner and that two components are involved in the binding, with apparent dissociation constants (Kd) of about 6 nM and 9 microM. The high affinity binding site has a maximal capacity of 25 pmol/mg protein...
Affinity labeling of calmodulin-binding proteins in skeletal muscle sarcoplasmi...
Vale, M. Graça P.125I-Calmodulin (125I-CaM) binding to sarcoplasmic reticulum (SR) membranes isolated from skeletal muscle cells was investigated, and the CaM receptors associated with the membrane were identified by using the photoaffinity cross-linker methyl-4-azidobenzimidate or the chemical cross-linker dithiobis-N-hydroxysuccinimidyl propionate. Exogenous CaM binds to CaM-depleted membranes in a Ca2+- or Mg2+-dependent way...
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