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  • Title: Calcium transport by bull spermatozoa plasma membranes.
    Author: Breitbart H, Rubinstein S.
    Journal: Biochim Biophys Acta; 1983 Jul 27; 732(2):464-8. PubMed ID: 6135447.
    Abstract:
    Plasma membrane isolated from frozen ejaculated bull spermatozoa were found to contain calcium transport activity. Thin-section electronmicrography of these membranes revealed relatively homogeneous vesicular membranes with sizes ranging from 2000 to 6000 A in diameter. Membrane vesicles that were exposed to oxalate as a calcium-trapping agent accumulated Ca2+ in the presence of Mg2+ and ATP. One microM of the calcium-ionophore A23187, added initially, completely inhibited net Ca2+ uptake and, if added later, caused the release of Ca2+ accumulated previously. An Arrhenius plot for the rate of Ca2+ uptake revealed a break at 32--33 degrees C, and Ea of 4.4 kcal/mol above the break and 32.2 kcal/mol below. The Ca+ uptake was inhibited by low concentrations of quercetin, which is known to be an inhibitor of (Ca2+ + Mg2+)-ATPase in many systems.
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