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Calcium ATPase Activities in Synaptic Plasma Membranes of Seizure‐Prone Mice
Author(s) -
Palayoor Sanjeewani T.,
Seyfried Thomas N.,
Bernard David J.
Publication year - 1986
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1986.tb01749.x
Subject(s) - calcium , synaptic membrane , neuroscience , membrane , chemistry , atpase , synaptic augmentation , synaptic plasticity , biology , biochemistry , enzyme , receptor , organic chemistry
Audiogenic seizure (AGS)‐susceptible DBA/2 (D2) mice have a significant reduction in brain Ca 2+ ‐ATPase activity compared to AGS‐resistant C57BL/6 (B6) mice. This reduction is inherited together with AGS susceptibility in B6 × D2 recombinant inbred strains. The Ca 2+ ‐ATPase reduction occurs in microsomes and synaptosomes, but not in mitochondria. This enzyme activity is measured at a high Ca 2+ concentration (2 m M ) with no added Mg 2+ or EGTA. We further studied this Ca 2+ ‐ATPase activity and a Mg 2+ ‐dependent (Ca 2+ + Mg 2+ ‐ATPase activity in synaptic plasma membranes (SPM) from the B6 and D2 strains. Using EGTA or CDTA to adjust free Ca 2+ concentrations, we measured Ca 2+ ‐ATPase activities at Ca 2+ concentrations from 0.8 μ M to 436 μ M. The Ca 2+ ATPase activity is consistently lower in the D2 than in the B6 SPM over all Ca 2+ concentrations. The basal Mg 2+ ATPase activity measured at 2 m M MgCl 2 , is also lower in SPM of D2 than B6 mice. Calcium stimulates the basal Mg 2+ ‐ATPase activity to the same extent in the SPM of the B6 and the D2 mice. Maximum stimulation in both strains occurs at 150 μ M added CaCl 2 (buffered with 100 μ M EGTA). Higher Ca 2+ concentrations inhibit this ATPase activity similarly in both strains. The EGTA‐EDTA washing of SPM significantly reduces by 50% the (Ca 2+ Mg 2+ )‐ATPase activities of both strains, whereas calmodulin treatment restored these activities. Neither of these treatments, however, has any noticeable effects on the Ca 2+ ‐ATPase activities of the strains. We conclude from this strain comparison that the Ca 2+ ‐ATPase and the (Ca 2+ + Mg 2+ )ATPase activities are different enzymes and that the Ca 2+ ‐ATPase activity in D2 mice is also deficient at low Ca 2+ concentrations.