Characterization of Calcium‐Activated and Magnesium‐Activated ATPases of Brain Nerve Endings

Abstract

The properties of Ca2+-activated and Mg2+-activated ATPases of nerve endings from mouse brain were investigated. Ca2+ and Mg2+ each can activate ATP hydrolysis in synaptosomes and its subfractions. Both Ca2+-ATPase and Mg2+-ATPase exhibit high and low affinity for their respective cations. At millimolar concentrations of Ca2+ or Mg2+, several nucleoside triphosphates could serve as substrate for the two enzymes and their specific activities were about three to four times higher in synaptic vesicles than in synaptosomal plasma membranes (SPM). Both in SPM and in synaptic vesicles the relative activity in the presence of Ca2+ was in the order of CTP greater than UTP greater than GTP = ATP, but with Mg2+ the activity was higher with ATP than with the other three triphosphates. Mg2+-ATPase was more active than Ca2+-ATPase in SPM, but in synaptic vesicles the two enzymes exhibited similar activity. Kinetic studies revealed that Mg2+-ATPase was inhibited by excess ATP and not by excess Mg2+. The simultaneous presence of Na+ + K+ stimulated Mg2+-ATPase and inhibited Ca2+-ATPase activity in intact synaptosomes and SPM. The stimulation of Mg2+-ATPase by Na+ + K+ was further increased by increasing Mg2+ concentration and was inhibited by Ca2+ and by ouabain. When Ca2+ and Mg2+ are present together in SPM or synaptic vesicles, the total Pi liberated by the two cations may either increase or decrease, depending on their relative concentrations. Kinetic analyses indicate that Ca2+ and Mg2+ bind independently to the enzyme alone or together at different sites. The results suggest that Ca2+-ATPase and Mg2+-ATPase in SPM or synaptic vesicles may be separate and distinct systems.

Effect of In Vivo l-Acetylcarnitine Administration on ATP-ases Enzyme Systems of Synaptic Plasma Membranes from Rat Cerebral Cortex

“…-ATP-ase, the K m value is 82.6 lM Ca 2? [56], suggesting that it is a ''capacitative'' component in the calcium extrusion mechanism, while the high-affinity Ca 2? -ATPase is an allosteric enzyme showing a K m = 1.33 lM Ca 2?…”

Magnesium lithospermate B possesses inhibitory activity on Na+,K+-ATPase and neuroprotective effects against ischemic stroke

“…The plasma membrane was isolated from the rat brain and heart at 4 °C according to the methods described by Lin and Way [13,16] . Briefly, the brain cortex or heart was homogenized with 10-20 volumes of 0.32 mmol/L sucrose solution containing 5.0 mmol/L 4-(2-hydroxyethyl)-1-piperazineethane-sulfonic acid (HEPES) and 1.0 mmol/L EDTA (pH 7.5).…”

The plasma membrane calcium pump: Functional domains, regulation of the activity, and tissue specificity of isoform expression

“…The presence of several Ca2+-ATPases in neuronal tissues (mainly synaptosomes) is now documented ( Hermoni-Levine and Rahamimoff, 1990;Hakim et al, 1982;Kaprielian et al, 1989;Lin and Way, 1984;Michaelis et al, 1987;Palayoor et al, 1986). A pump described in cerebellar Purkinje cells (Kaprielian et a]., 1989) corresponds to the Ca*+-ATPase of the sarcoplasmatic reticulum (SERCA), but the presence of the plasma membrane Ca2+-ATPase in neuronal tissues can be also considered as conclusively documented (Hakim et al,198 1 ). cDNA cloning and mRNA analysis by PCR has detected the transcripts of the four gene products and their different splice forms in neuronal tissues of different species ( Brandt et a]., 1992;Brandt and Neve, 1992c;Burk and Shull, 1992;Greeb, and Shull, 1989;Keeton et al, 1993;Shull and Greeb, 1989;Stauffer et al, 1993).…”